FFmpeg/libavformat/matroskadec.c

/*
 * Matroska file demuxer (no muxer yet)
 * Copyright (c) 2003-2004 The ffmpeg Project
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * FFmpeg is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

/**
 * @file matroskadec.c
 * Matroska file demuxer
 * by Ronald Bultje <rbultje@ronald.bitfreak.net>
 * with a little help from Moritz Bunkus <moritz@bunkus.org>
 * Specs available on the matroska project page:
 * http://www.matroska.org/.
 */

#include "avformat.h"
/* For codec_get_id(). */
#include "riff.h"
#include "isom.h"
#include "matroska.h"
#include "libavcodec/mpeg4audio.h"
#include "libavutil/intfloat_readwrite.h"
#include "libavutil/avstring.h"
#include "libavutil/lzo.h"
#ifdef CONFIG_ZLIB
#include <zlib.h>
#endif
#ifdef CONFIG_BZLIB
#include <bzlib.h>
#endif

typedef enum {
    EBML_NONE,
    EBML_UINT,
    EBML_FLOAT,
    EBML_STR,
    EBML_UTF8,
    EBML_BIN,
    EBML_NEST,
    EBML_PASS,
    EBML_STOP,
} EbmlType;

typedef const struct EbmlSyntax {
    uint32_t id;
    EbmlType type;
    int list_elem_size;
    int data_offset;
    union {
        uint64_t    u;
        double      f;
        const char *s;
        const struct EbmlSyntax *n;
    } def;
} EbmlSyntax;

typedef struct {
    int nb_elem;
    void *elem;
} EbmlList;

typedef struct {
    int      size;
    uint8_t *data;
    int64_t  pos;
} EbmlBin;

typedef struct {
    uint64_t version;
    uint64_t max_size;
    uint64_t id_length;
    char    *doctype;
    uint64_t doctype_version;
} Ebml;

typedef struct {
    uint64_t algo;
    EbmlBin  settings;
} MatroskaTrackCompression;

typedef struct {
    uint64_t scope;
    uint64_t type;
    MatroskaTrackCompression compression;
} MatroskaTrackEncoding;

typedef struct {
    double   frame_rate;
    uint64_t display_width;
    uint64_t display_height;
    uint64_t pixel_width;
    uint64_t pixel_height;
    uint64_t fourcc;
} MatroskaTrackVideo;

typedef struct {
    double   samplerate;
    double   out_samplerate;
    uint64_t bitdepth;
    uint64_t channels;

    /* real audio header (extracted from extradata) */
    int      coded_framesize;
    int      sub_packet_h;
    int      frame_size;
    int      sub_packet_size;
    int      sub_packet_cnt;
    int      pkt_cnt;
    uint8_t *buf;
} MatroskaTrackAudio;

typedef struct {
    uint64_t num;
    uint64_t type;
    char    *codec_id;
    EbmlBin  codec_priv;
    char    *language;
    double time_scale;
    uint64_t default_duration;
    uint64_t flag_default;
    MatroskaTrackVideo video;
    MatroskaTrackAudio audio;
    EbmlList encodings;

    AVStream *stream;
} MatroskaTrack;

typedef struct {
    char *filename;
    char *mime;
    EbmlBin bin;
} MatroskaAttachement;

typedef struct {
    uint64_t start;
    uint64_t end;
    uint64_t uid;
    char    *title;
} MatroskaChapter;

typedef struct {
    uint64_t track;
    uint64_t pos;
} MatroskaIndexPos;

typedef struct {
    uint64_t time;
    EbmlList pos;
} MatroskaIndex;

typedef struct {
    uint64_t id;
    uint64_t pos;
} MatroskaSeekhead;

typedef struct MatroskaLevel {
    uint64_t start;
    uint64_t length;
} MatroskaLevel;

typedef struct MatroskaDemuxContext {
    AVFormatContext *ctx;

    /* ebml stuff */
    int num_levels;
    MatroskaLevel levels[EBML_MAX_DEPTH];
    int level_up;

    /* timescale in the file */
    uint64_t time_scale;
    double   duration;
    char    *title;
    EbmlList tracks;
    EbmlList attachments;
    EbmlList chapters;
    EbmlList index;
    EbmlList seekhead;

    /* num_streams is the number of streams that av_new_stream() was called
     * for ( = that are available to the calling program). */
    int num_streams;

    /* cache for ID peeking */
    uint32_t peek_id;

    /* byte position of the segment inside the stream */
    offset_t segment_start;

    /* The packet queue. */
    AVPacket **packets;
    int num_packets;

    /* have we already parse metadata/cues/clusters? */
    int metadata_parsed;
    int index_parsed;
    int done;

    /* What to skip before effectively reading a packet. */
    int skip_to_keyframe;
    AVStream *skip_to_stream;
} MatroskaDemuxContext;

#define ARRAY_SIZE(x)  (sizeof(x)/sizeof(*x))

static EbmlSyntax ebml_header[] = {
    { EBML_ID_EBMLREADVERSION,        EBML_UINT, 0, offsetof(Ebml,version), {.u=EBML_VERSION} },
    { EBML_ID_EBMLMAXSIZELENGTH,      EBML_UINT, 0, offsetof(Ebml,max_size), {.u=8} },
    { EBML_ID_EBMLMAXIDLENGTH,        EBML_UINT, 0, offsetof(Ebml,id_length), {.u=4} },
    { EBML_ID_DOCTYPE,                EBML_STR,  0, offsetof(Ebml,doctype), {.s="(none)"} },
    { EBML_ID_DOCTYPEREADVERSION,     EBML_UINT, 0, offsetof(Ebml,doctype_version), {.u=1} },
    { EBML_ID_EBMLVERSION,            EBML_NONE },
    { EBML_ID_DOCTYPEVERSION,         EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax ebml_syntax[] = {
    { EBML_ID_HEADER,                 EBML_NEST, 0, 0, {.n=ebml_header} },
    { 0 }
};

static EbmlSyntax matroska_info[] = {
    { MATROSKA_ID_TIMECODESCALE,      EBML_UINT,  0, offsetof(MatroskaDemuxContext,time_scale), {.u=1000000} },
    { MATROSKA_ID_DURATION,           EBML_FLOAT, 0, offsetof(MatroskaDemuxContext,duration) },
    { MATROSKA_ID_TITLE,              EBML_UTF8,  0, offsetof(MatroskaDemuxContext,title) },
    { MATROSKA_ID_WRITINGAPP,         EBML_NONE },
    { MATROSKA_ID_MUXINGAPP,          EBML_NONE },
    { MATROSKA_ID_DATEUTC,            EBML_NONE },
    { MATROSKA_ID_SEGMENTUID,         EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track_video[] = {
    { MATROSKA_ID_VIDEOFRAMERATE,     EBML_FLOAT,0, offsetof(MatroskaTrackVideo,frame_rate) },
    { MATROSKA_ID_VIDEODISPLAYWIDTH,  EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_width) },
    { MATROSKA_ID_VIDEODISPLAYHEIGHT, EBML_UINT, 0, offsetof(MatroskaTrackVideo,display_height) },
    { MATROSKA_ID_VIDEOPIXELWIDTH,    EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_width) },
    { MATROSKA_ID_VIDEOPIXELHEIGHT,   EBML_UINT, 0, offsetof(MatroskaTrackVideo,pixel_height) },
    { MATROSKA_ID_VIDEOCOLORSPACE,    EBML_UINT, 0, offsetof(MatroskaTrackVideo,fourcc) },
    { MATROSKA_ID_VIDEOFLAGINTERLACED,EBML_NONE },
    { MATROSKA_ID_VIDEOSTEREOMODE,    EBML_NONE },
    { MATROSKA_ID_VIDEOASPECTRATIO,   EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track_audio[] = {
    { MATROSKA_ID_AUDIOSAMPLINGFREQ,  EBML_FLOAT,0, offsetof(MatroskaTrackAudio,samplerate), {.f=8000.0} },
    { MATROSKA_ID_AUDIOOUTSAMPLINGFREQ,EBML_FLOAT,0,offsetof(MatroskaTrackAudio,out_samplerate) },
    { MATROSKA_ID_AUDIOBITDEPTH,      EBML_UINT, 0, offsetof(MatroskaTrackAudio,bitdepth) },
    { MATROSKA_ID_AUDIOCHANNELS,      EBML_UINT, 0, offsetof(MatroskaTrackAudio,channels), {.u=1} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track_encoding_compression[] = {
    { MATROSKA_ID_ENCODINGCOMPALGO,   EBML_UINT, 0, offsetof(MatroskaTrackCompression,algo), {.u=0} },
    { MATROSKA_ID_ENCODINGCOMPSETTINGS,EBML_BIN, 0, offsetof(MatroskaTrackCompression,settings) },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track_encoding[] = {
    { MATROSKA_ID_ENCODINGSCOPE,      EBML_UINT, 0, offsetof(MatroskaTrackEncoding,scope), {.u=1} },
    { MATROSKA_ID_ENCODINGTYPE,       EBML_UINT, 0, offsetof(MatroskaTrackEncoding,type), {.u=0} },
    { MATROSKA_ID_ENCODINGCOMPRESSION,EBML_NEST, 0, offsetof(MatroskaTrackEncoding,compression), {.n=matroska_track_encoding_compression} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track_encodings[] = {
    { MATROSKA_ID_TRACKCONTENTENCODING, EBML_NEST, sizeof(MatroskaTrackEncoding), offsetof(MatroskaTrack,encodings), {.n=matroska_track_encoding} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_track[] = {
    { MATROSKA_ID_TRACKNUMBER,          EBML_UINT, 0, offsetof(MatroskaTrack,num) },
    { MATROSKA_ID_TRACKTYPE,            EBML_UINT, 0, offsetof(MatroskaTrack,type) },
    { MATROSKA_ID_CODECID,              EBML_STR,  0, offsetof(MatroskaTrack,codec_id) },
    { MATROSKA_ID_CODECPRIVATE,         EBML_BIN,  0, offsetof(MatroskaTrack,codec_priv) },
    { MATROSKA_ID_TRACKLANGUAGE,        EBML_UTF8, 0, offsetof(MatroskaTrack,language), {.s="eng"} },
    { MATROSKA_ID_TRACKDEFAULTDURATION, EBML_UINT, 0, offsetof(MatroskaTrack,default_duration) },
    { MATROSKA_ID_TRACKTIMECODESCALE,   EBML_FLOAT,0, offsetof(MatroskaTrack,time_scale), {.f=1.0} },
    { MATROSKA_ID_TRACKFLAGDEFAULT,     EBML_UINT, 0, offsetof(MatroskaTrack,flag_default), {.u=1} },
    { MATROSKA_ID_TRACKVIDEO,           EBML_NEST, 0, offsetof(MatroskaTrack,video), {.n=matroska_track_video} },
    { MATROSKA_ID_TRACKAUDIO,           EBML_NEST, 0, offsetof(MatroskaTrack,audio), {.n=matroska_track_audio} },
    { MATROSKA_ID_TRACKCONTENTENCODINGS,EBML_NEST, 0, 0, {.n=matroska_track_encodings} },
    { MATROSKA_ID_TRACKUID,             EBML_NONE },
    { MATROSKA_ID_TRACKNAME,            EBML_NONE },
    { MATROSKA_ID_TRACKFLAGENABLED,     EBML_NONE },
    { MATROSKA_ID_TRACKFLAGFORCED,      EBML_NONE },
    { MATROSKA_ID_TRACKFLAGLACING,      EBML_NONE },
    { MATROSKA_ID_CODECNAME,            EBML_NONE },
    { MATROSKA_ID_CODECDECODEALL,       EBML_NONE },
    { MATROSKA_ID_CODECINFOURL,         EBML_NONE },
    { MATROSKA_ID_CODECDOWNLOADURL,     EBML_NONE },
    { MATROSKA_ID_TRACKMINCACHE,        EBML_NONE },
    { MATROSKA_ID_TRACKMAXCACHE,        EBML_NONE },
    { EBML_ID_VOID,                     EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_tracks[] = {
    { MATROSKA_ID_TRACKENTRY,         EBML_NEST, sizeof(MatroskaTrack), offsetof(MatroskaDemuxContext,tracks), {.n=matroska_track} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_attachment[] = {
    { MATROSKA_ID_FILENAME,           EBML_UTF8, 0, offsetof(MatroskaAttachement,filename) },
    { MATROSKA_ID_FILEMIMETYPE,       EBML_STR,  0, offsetof(MatroskaAttachement,mime) },
    { MATROSKA_ID_FILEDATA,           EBML_BIN,  0, offsetof(MatroskaAttachement,bin) },
    { MATROSKA_ID_FILEUID,            EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_attachments[] = {
    { MATROSKA_ID_ATTACHEDFILE,       EBML_NEST, sizeof(MatroskaAttachement), offsetof(MatroskaDemuxContext,attachments), {.n=matroska_attachment} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_chapter_display[] = {
    { MATROSKA_ID_CHAPSTRING,         EBML_UTF8, 0, offsetof(MatroskaChapter,title) },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_chapter_entry[] = {
    { MATROSKA_ID_CHAPTERTIMESTART,   EBML_UINT, 0, offsetof(MatroskaChapter,start), {.u=AV_NOPTS_VALUE} },
    { MATROSKA_ID_CHAPTERTIMEEND,     EBML_UINT, 0, offsetof(MatroskaChapter,end), {.u=AV_NOPTS_VALUE} },
    { MATROSKA_ID_CHAPTERUID,         EBML_UINT, 0, offsetof(MatroskaChapter,uid) },
    { MATROSKA_ID_CHAPTERDISPLAY,     EBML_NEST, 0, 0, {.n=matroska_chapter_display} },
    { MATROSKA_ID_CHAPTERFLAGHIDDEN,  EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_chapter[] = {
    { MATROSKA_ID_CHAPTERATOM,        EBML_NEST, sizeof(MatroskaChapter), offsetof(MatroskaDemuxContext,chapters), {.n=matroska_chapter_entry} },
    { MATROSKA_ID_EDITIONUID,         EBML_NONE },
    { MATROSKA_ID_EDITIONFLAGHIDDEN,  EBML_NONE },
    { MATROSKA_ID_EDITIONFLAGDEFAULT, EBML_NONE },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_chapters[] = {
    { MATROSKA_ID_EDITIONENTRY,       EBML_NEST, 0, 0, {.n=matroska_chapter} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_index_pos[] = {
    { MATROSKA_ID_CUETRACK,           EBML_UINT, 0, offsetof(MatroskaIndexPos,track) },
    { MATROSKA_ID_CUECLUSTERPOSITION, EBML_UINT, 0, offsetof(MatroskaIndexPos,pos)   },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_index_entry[] = {
    { MATROSKA_ID_CUETIME,            EBML_UINT, 0, offsetof(MatroskaIndex,time) },
    { MATROSKA_ID_CUETRACKPOSITION,   EBML_NEST, sizeof(MatroskaIndexPos), offsetof(MatroskaIndex,pos), {.n=matroska_index_pos} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_index[] = {
    { MATROSKA_ID_POINTENTRY,         EBML_NEST, sizeof(MatroskaIndex), offsetof(MatroskaDemuxContext,index), {.n=matroska_index_entry} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_tags[] = {
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_seekhead_entry[] = {
    { MATROSKA_ID_SEEKID,             EBML_UINT, 0, offsetof(MatroskaSeekhead,id) },
    { MATROSKA_ID_SEEKPOSITION,       EBML_UINT, 0, offsetof(MatroskaSeekhead,pos), {.u=-1} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

static EbmlSyntax matroska_seekhead[] = {
    { MATROSKA_ID_SEEKENTRY,          EBML_NEST, sizeof(MatroskaSeekhead), offsetof(MatroskaDemuxContext,seekhead), {.n=matroska_seekhead_entry} },
    { EBML_ID_VOID,                   EBML_NONE },
    { 0 }
};

/*
 * The first few functions handle EBML file parsing. The rest
 * is the document interpretation. Matroska really just is a
 * EBML file.
 */

/*
 * Return: the amount of levels in the hierarchy that the
 * current element lies higher than the previous one.
 * The opposite isn't done - that's auto-done using master
 * element reading.
 */

static int
ebml_read_element_level_up (MatroskaDemuxContext *matroska)
{
    ByteIOContext *pb = matroska->ctx->pb;
    offset_t pos = url_ftell(pb);
    int num = 0;

    while (matroska->num_levels > 0) {
        MatroskaLevel *level = &matroska->levels[matroska->num_levels - 1];

        if (pos >= level->start + level->length) {
            matroska->num_levels--;
            num++;
        } else {
            break;
        }
    }

    return num;
}

/*
 * Read: an "EBML number", which is defined as a variable-length
 * array of bytes. The first byte indicates the length by giving a
 * number of 0-bits followed by a one. The position of the first
 * "one" bit inside the first byte indicates the length of this
 * number.
 * Returns: num. of bytes read. < 0 on error.
 */

static int
ebml_read_num (MatroskaDemuxContext *matroska,
               int                   max_size,
               uint64_t             *number)
{
    ByteIOContext *pb = matroska->ctx->pb;
    int len_mask = 0x80, read = 1, n = 1;
    int64_t total = 0;

    /* the first byte tells us the length in bytes - get_byte() can normally
     * return 0, but since that's not a valid first ebmlID byte, we can
     * use it safely here to catch EOS. */
    if (!(total = get_byte(pb))) {
        /* we might encounter EOS here */
        if (!url_feof(pb)) {
            offset_t pos = url_ftell(pb);
            av_log(matroska->ctx, AV_LOG_ERROR,
                   "Read error at pos. %"PRIu64" (0x%"PRIx64")\n",
                   pos, pos);
        }
        return AVERROR(EIO); /* EOS or actual I/O error */
    }

    /* get the length of the EBML number */
    while (read <= max_size && !(total & len_mask)) {
        read++;
        len_mask >>= 1;
    }
    if (read > max_size) {
        offset_t pos = url_ftell(pb) - 1;
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid EBML number size tag 0x%02x at pos %"PRIu64" (0x%"PRIx64")\n",
               (uint8_t) total, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    /* read out length */
    total &= ~len_mask;
    while (n++ < read)
        total = (total << 8) | get_byte(pb);

    *number = total;

    return read;
}

/*
 * Read: the element content data ID.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_id (MatroskaDemuxContext *matroska,
                      uint32_t             *id,
                      int                  *level_up)
{
    int read;
    uint64_t total;

    /* if we re-call this, use our cached ID */
    if (matroska->peek_id != 0) {
        if (level_up)
            *level_up = 0;
        *id = matroska->peek_id;
        return 0;
    }

    /* read out the "EBML number", include tag in ID */
    if ((read = ebml_read_num(matroska, 4, &total)) < 0)
        return read;
    *id = matroska->peek_id  = total | (1 << (read * 7));

    /* level tracking */
    if (level_up)
        *level_up = ebml_read_element_level_up(matroska);

    return read;
}

/*
 * Read: element content length.
 * Return: the number of bytes read or < 0 on error.
 */

static int
ebml_read_element_length (MatroskaDemuxContext *matroska,
                          uint64_t             *length)
{
    /* clear cache since we're now beyond that data point */
    matroska->peek_id = 0;

    /* read out the "EBML number", include tag in ID */
    return ebml_read_num(matroska, 8, length);
}

/*
 * Return: the ID of the next element, or 0 on error.
 * Level_up contains the amount of levels that this
 * next element lies higher than the previous one.
 */

static uint32_t
ebml_peek_id (MatroskaDemuxContext *matroska,
              int                  *level_up)
{
    uint32_t id;

    if (ebml_read_element_id(matroska, &id, level_up) < 0)
        return 0;

    return id;
}

/*
 * Seek to a given offset.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_seek (MatroskaDemuxContext *matroska,
                offset_t              offset)
{
    ByteIOContext *pb = matroska->ctx->pb;

    /* clear ID cache, if any */
    matroska->peek_id = 0;

    return (url_fseek(pb, offset, SEEK_SET) == offset) ? 0 : -1;
}

/*
 * Skip the next element.
 * 0 is success, -1 is failure.
 */

static int
ebml_read_skip (MatroskaDemuxContext *matroska)
{
    ByteIOContext *pb = matroska->ctx->pb;
    uint32_t id;
    uint64_t length;
    int res;

    if ((res = ebml_read_element_id(matroska, &id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &length)) < 0)
        return res;

    url_fskip(pb, length);

    return 0;
}

/*
 * Read the next element as an unsigned int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_uint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                uint64_t             *num)
{
    ByteIOContext *pb = matroska->ctx->pb;
    int n = 0, size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;
    if (size < 1 || size > 8) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid uint element size %d at position %"PRId64" (0x%"PRIx64")\n",
                size, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    /* big-endian ordening; build up number */
    *num = 0;
    while (n++ < size)
        *num = (*num << 8) | get_byte(pb);

    return 0;
}

/*
 * Read the next element as a signed int.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_sint (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                int64_t              *num)
{
    ByteIOContext *pb = matroska->ctx->pb;
    int size, n = 1, negative = 0, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;
    if (size < 1 || size > 8) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid sint element size %d at position %"PRId64" (0x%"PRIx64")\n",
                size, pos, pos);
        return AVERROR_INVALIDDATA;
    }
    if ((*num = get_byte(pb)) & 0x80) {
        negative = 1;
        *num &= ~0x80;
    }
    while (n++ < size)
        *num = (*num << 8) | get_byte(pb);

    /* make signed */
    if (negative)
        *num = *num - (1LL << ((8 * size) - 1));

    return 0;
}

/*
 * Read the next element as a float.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_float (MatroskaDemuxContext *matroska,
                 uint32_t             *id,
                 double               *num)
{
    ByteIOContext *pb = matroska->ctx->pb;
    int size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;

    if (size == 4) {
        *num= av_int2flt(get_be32(pb));
    } else if(size==8){
        *num= av_int2dbl(get_be64(pb));
    } else{
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Invalid float element size %d at position %"PRIu64" (0x%"PRIx64")\n",
               size, pos, pos);
        return AVERROR_INVALIDDATA;
    }

    return 0;
}

/*
 * Read the next element as an ASCII string.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_ascii (MatroskaDemuxContext *matroska,
                 uint32_t             *id,
                 char                **str)
{
    ByteIOContext *pb = matroska->ctx->pb;
    int size, res;
    uint64_t rlength;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    size = rlength;

    /* ebml strings are usually not 0-terminated, so we allocate one
     * byte more, read the string and NULL-terminate it ourselves. */
    if (size < 0 || !(*str = av_malloc(size + 1))) {
        av_log(matroska->ctx, AV_LOG_ERROR, "Memory allocation failed\n");
        return AVERROR(ENOMEM);
    }
    if (get_buffer(pb, (uint8_t *) *str, size) != size) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Read error at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
        av_free(*str);
        return AVERROR(EIO);
    }
    (*str)[size] = '\0';

    return 0;
}

/*
 * Read the next element as a UTF-8 string.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_utf8 (MatroskaDemuxContext *matroska,
                uint32_t             *id,
                char                **str)
{
  return ebml_read_ascii(matroska, id, str);
}

/*
 * Read the next element, but only the header. The contents
 * are supposed to be sub-elements which can be read separately.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_master (MatroskaDemuxContext *matroska,
                  uint32_t             *id)
{
    ByteIOContext *pb = matroska->ctx->pb;
    uint64_t length;
    MatroskaLevel *level;
    int res;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &length)) < 0)
        return res;

    /* protect... (Heaven forbids that the '>' is true) */
    if (matroska->num_levels >= EBML_MAX_DEPTH) {
        av_log(matroska->ctx, AV_LOG_ERROR,
               "File moves beyond max. allowed depth (%d)\n", EBML_MAX_DEPTH);
        return AVERROR(ENOSYS);
    }

    /* remember level */
    level = &matroska->levels[matroska->num_levels++];
    level->start = url_ftell(pb);
    level->length = length;

    return 0;
}

/*
 * Read the next element as binary data.
 * 0 is success, < 0 is failure.
 */

static int
ebml_read_binary (MatroskaDemuxContext *matroska,
                  uint32_t             *id,
                  uint8_t             **binary,
                  int                  *size)
{
    ByteIOContext *pb = matroska->ctx->pb;
    uint64_t rlength;
    int res;

    if ((res = ebml_read_element_id(matroska, id, NULL)) < 0 ||
        (res = ebml_read_element_length(matroska, &rlength)) < 0)
        return res;
    *size = rlength;

    if (!(*binary = av_malloc(*size))) {
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Memory allocation error\n");
        return AVERROR(ENOMEM);
    }

    if (get_buffer(pb, *binary, *size) != *size) {
        offset_t pos = url_ftell(pb);
        av_log(matroska->ctx, AV_LOG_ERROR,
               "Read error at pos. %"PRIu64" (0x%"PRIx64")\n", pos, pos);
        return AVERROR(EIO);
    }

    return 0;
}

/*
 * Read signed/unsigned "EBML" numbers.
 * Return: number of bytes processed, < 0 on error.
 * XXX: use ebml_read_num().
 */

static int
matroska_ebmlnum_uint (uint8_t  *data,
                       uint32_t  size,
                       uint64_t *num)
{
    int len_mask = 0x80, read = 1, n = 1, num_ffs = 0;
    uint64_t total;

    if (size <= 0)
        return AVERROR_INVALIDDATA;

    total = data[0];
    while (read <= 8 && !(total & len_mask)) {
        read++;
        len_mask >>= 1;
    }
    if (read > 8)
        return AVERROR_INVALIDDATA;

    if ((total &= (len_mask - 1)) == len_mask - 1)
        num_ffs++;
    if (size < read)
        return AVERROR_INVALIDDATA;
    while (n < read) {
        if (data[n] == 0xff)
            num_ffs++;
        total = (total << 8) | data[n];
        n++;
    }

    if (read == num_ffs)
        *num = (uint64_t)-1;
    else
        *num = total;

    return read;
}

/*
 * Same as above, but signed.
 */

static int
matroska_ebmlnum_sint (uint8_t  *data,
                       uint32_t  size,
                       int64_t  *num)
{
    uint64_t unum;
    int res;

    /* read as unsigned number first */
    if ((res = matroska_ebmlnum_uint(data, size, &unum)) < 0)
        return res;

    /* make signed (weird way) */
    if (unum == (uint64_t)-1)
        *num = INT64_MAX;
    else
        *num = unum - ((1LL << ((7 * res) - 1)) - 1);

    return res;
}


static MatroskaTrack *
matroska_find_track_by_num (MatroskaDemuxContext *matroska,
                            int                   num)
{
    MatroskaTrack *tracks = matroska->tracks.elem;
    int i;

    for (i=0; i < matroska->tracks.nb_elem; i++)
        if (tracks[i].num == num)
            return &tracks[i];

    av_log(matroska->ctx, AV_LOG_ERROR, "Invalid track number %d\n", num);
    return NULL;
}


/*
 * Put one packet in an application-supplied AVPacket struct.
 * Returns 0 on success or -1 on failure.
 */

static int
matroska_deliver_packet (MatroskaDemuxContext *matroska,
                         AVPacket             *pkt)
{
    if (matroska->num_packets > 0) {
        memcpy(pkt, matroska->packets[0], sizeof(AVPacket));
        av_free(matroska->packets[0]);
        if (matroska->num_packets > 1) {
            memmove(&matroska->packets[0], &matroska->packets[1],
                    (matroska->num_packets - 1) * sizeof(AVPacket *));
            matroska->packets =
                av_realloc(matroska->packets, (matroska->num_packets - 1) *
                           sizeof(AVPacket *));
        } else {
            av_freep(&matroska->packets);
        }
        matroska->num_packets--;
        return 0;
    }

    return -1;
}

/*
 * Put a packet into our internal queue. Will be delivered to the
 * user/application during the next get_packet() call.
 */

static void
matroska_queue_packet (MatroskaDemuxContext *matroska,
                       AVPacket             *pkt)
{
    matroska->packets =
        av_realloc(matroska->packets, (matroska->num_packets + 1) *
                   sizeof(AVPacket *));
    matroska->packets[matroska->num_packets] = pkt;
    matroska->num_packets++;
}

/*
 * Free all packets in our internal queue.
 */
static void
matroska_clear_queue (MatroskaDemuxContext *matroska)
{
    if (matroska->packets) {
        int n;
        for (n = 0; n < matroska->num_packets; n++) {
            av_free_packet(matroska->packets[n]);
            av_free(matroska->packets[n]);
        }
        av_free(matroska->packets);
        matroska->packets = NULL;
        matroska->num_packets = 0;
    }
}


/*
 * Autodetecting...
 */

static int
matroska_probe (AVProbeData *p)
{
    uint64_t total = 0;
    int len_mask = 0x80, size = 1, n = 1;
    uint8_t probe_data[] = { 'm', 'a', 't', 'r', 'o', 's', 'k', 'a' };

    /* ebml header? */
    if (AV_RB32(p->buf) != EBML_ID_HEADER)
        return 0;

    /* length of header */
    total = p->buf[4];
    while (size <= 8 && !(total & len_mask)) {
        size++;
        len_mask >>= 1;
    }
    if (size > 8)
      return 0;
    total &= (len_mask - 1);
    while (n < size)
        total = (total << 8) | p->buf[4 + n++];

    /* does the probe data contain the whole header? */
    if (p->buf_size < 4 + size + total)
      return 0;

    /* the header must contain the document type 'matroska'. For now,
     * we don't parse the whole header but simply check for the
     * availability of that array of characters inside the header.
     * Not fully fool-proof, but good enough. */
    for (n = 4 + size; n <= 4 + size + total - sizeof(probe_data); n++)
        if (!memcmp (&p->buf[n], probe_data, sizeof(probe_data)))
            return AVPROBE_SCORE_MAX;

    return 0;
}

/*
 * From here on, it's all XML-style DTD stuff... Needs no comments.
 */

static int ebml_parse(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                      void *data, uint32_t expected_id, int once);

static int ebml_parse_elem(MatroskaDemuxContext *matroska,
                           EbmlSyntax *syntax, void *data)
{
    uint32_t id = syntax->id;
    EbmlBin *bin;
    int res;

    data = (char *)data + syntax->data_offset;
    if (syntax->list_elem_size) {
        EbmlList *list = data;
        list->elem = av_realloc(list->elem, (list->nb_elem+1)*syntax->list_elem_size);
        data = (char*)list->elem + list->nb_elem*syntax->list_elem_size;
        memset(data, 0, syntax->list_elem_size);
        list->nb_elem++;
    }
    bin = data;

    switch (syntax->type) {
    case EBML_UINT:  return ebml_read_uint (matroska, &id, data);
    case EBML_FLOAT: return ebml_read_float(matroska, &id, data);
    case EBML_STR:
    case EBML_UTF8:  av_free(*(char **)data);
                     return ebml_read_ascii(matroska, &id, data);
    case EBML_BIN:   av_free(bin->data);
                     bin->pos = url_ftell(matroska->ctx->pb);
                     return ebml_read_binary(matroska, &id, &bin->data,
                                                            &bin->size);
    case EBML_NEST:  if ((res=ebml_read_master(matroska, &id)) < 0)
                         return res;
                     if (id == MATROSKA_ID_SEGMENT)
                         matroska->segment_start = url_ftell(matroska->ctx->pb);
                     return ebml_parse(matroska, syntax->def.n, data, 0, 0);
    case EBML_PASS:  return ebml_parse(matroska, syntax->def.n, data, 0, 1);
    case EBML_STOP:  *(int *)data = 1;      return 1;
    default:         return ebml_read_skip(matroska);
    }
}

static int ebml_parse_id(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                         uint32_t id, void *data)
{
    int i;
    for (i=0; syntax[i].id; i++)
        if (id == syntax[i].id)
            break;
    if (!syntax[i].id)
        av_log(matroska->ctx, AV_LOG_INFO, "Unknown entry 0x%X\n", id);
    return ebml_parse_elem(matroska, &syntax[i], data);
}

static int ebml_parse(MatroskaDemuxContext *matroska, EbmlSyntax *syntax,
                      void *data, uint32_t expected_id, int once)
{
    int i, res = 0;
    uint32_t id = 0;

    for (i=0; syntax[i].id; i++)
        switch (syntax[i].type) {
        case EBML_UINT:
            *(uint64_t *)((char *)data+syntax[i].data_offset) = syntax[i].def.u;
            break;
        case EBML_FLOAT:
            *(double   *)((char *)data+syntax[i].data_offset) = syntax[i].def.f;
            break;
        case EBML_STR:
        case EBML_UTF8:
            *(char    **)((char *)data+syntax[i].data_offset) = av_strdup(syntax[i].def.s);
            break;
        }

    if (expected_id) {
        res = ebml_read_master(matroska, &id);
        if (id != expected_id)
            return AVERROR_INVALIDDATA;
        if (id == MATROSKA_ID_SEGMENT)
            matroska->segment_start = url_ftell(matroska->ctx->pb);
    }

    while (!res) {
        if (!(id = ebml_peek_id(matroska, &matroska->level_up))) {
            res = AVERROR(EIO);
            break;
        } else if (matroska->level_up) {
            matroska->level_up--;
            break;
        }

        res = ebml_parse_id(matroska, syntax, id, data);
        if (once)
            break;


        if (matroska->level_up) {
            matroska->level_up--;
            break;
        }
    }

    return res;
}

static void ebml_free(EbmlSyntax *syntax, void *data)
{
    int i, j;
    for (i=0; syntax[i].id; i++) {
        void *data_off = (char *)data + syntax[i].data_offset;
        switch (syntax[i].type) {
        case EBML_STR:
        case EBML_UTF8:  av_freep(data_off);                      break;
        case EBML_BIN:   av_freep(&((EbmlBin *)data_off)->data);  break;
        case EBML_NEST:
            if (syntax[i].list_elem_size) {
                EbmlList *list = data_off;
                char *ptr = list->elem;
                for (j=0; j<list->nb_elem; j++, ptr+=syntax[i].list_elem_size)
                    ebml_free(syntax[i].def.n, ptr);
                av_free(list->elem);
            } else
                ebml_free(syntax[i].def.n, data_off);
        default:  break;
        }
    }
}

static int
matroska_parse_info (MatroskaDemuxContext *matroska)
{
    int res = ebml_parse(matroska, matroska_info, matroska, MATROSKA_ID_INFO, 0);

    if (matroska->duration)
        matroska->ctx->duration = matroska->duration * matroska->time_scale
                                  * 1000 / AV_TIME_BASE;
    if (matroska->title)
        strncpy(matroska->ctx->title, matroska->title,
                sizeof(matroska->ctx->title)-1);

    return res;
}

static int
matroska_decode_buffer(uint8_t** buf, int* buf_size, MatroskaTrack *track)
{
    MatroskaTrackEncoding *encodings = track->encodings.elem;
    uint8_t* data = *buf;
    int isize = *buf_size;
    uint8_t* pkt_data = NULL;
    int pkt_size = isize;
    int result = 0;
    int olen;

    switch (encodings[0].compression.algo) {
    case MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP:
        return encodings[0].compression.settings.size;
    case MATROSKA_TRACK_ENCODING_COMP_LZO:
        do {
            olen = pkt_size *= 3;
            pkt_data = av_realloc(pkt_data,
                                  pkt_size+LZO_OUTPUT_PADDING);
            result = lzo1x_decode(pkt_data, &olen, data, &isize);
        } while (result==LZO_OUTPUT_FULL && pkt_size<10000000);
        if (result)
            goto failed;
        pkt_size -= olen;
        break;
#ifdef CONFIG_ZLIB
    case MATROSKA_TRACK_ENCODING_COMP_ZLIB: {
        z_stream zstream = {0};
        if (inflateInit(&zstream) != Z_OK)
            return -1;
        zstream.next_in = data;
        zstream.avail_in = isize;
        do {
            pkt_size *= 3;
            pkt_data = av_realloc(pkt_data, pkt_size);
            zstream.avail_out = pkt_size - zstream.total_out;
            zstream.next_out = pkt_data + zstream.total_out;
            result = inflate(&zstream, Z_NO_FLUSH);
        } while (result==Z_OK && pkt_size<10000000);
        pkt_size = zstream.total_out;
        inflateEnd(&zstream);
        if (result != Z_STREAM_END)
            goto failed;
        break;
    }
#endif
#ifdef CONFIG_BZLIB
    case MATROSKA_TRACK_ENCODING_COMP_BZLIB: {
        bz_stream bzstream = {0};
        if (BZ2_bzDecompressInit(&bzstream, 0, 0) != BZ_OK)
            return -1;
        bzstream.next_in = data;
        bzstream.avail_in = isize;
        do {
            pkt_size *= 3;
            pkt_data = av_realloc(pkt_data, pkt_size);
            bzstream.avail_out = pkt_size - bzstream.total_out_lo32;
            bzstream.next_out = pkt_data + bzstream.total_out_lo32;
            result = BZ2_bzDecompress(&bzstream);
        } while (result==BZ_OK && pkt_size<10000000);
        pkt_size = bzstream.total_out_lo32;
        BZ2_bzDecompressEnd(&bzstream);
        if (result != BZ_STREAM_END)
            goto failed;
        break;
    }
#endif
    }

    *buf = pkt_data;
    *buf_size = pkt_size;
    return 0;
 failed:
    av_free(pkt_data);
    return -1;
}

static int
matroska_parse_tracks (MatroskaDemuxContext *matroska)
{
    MatroskaTrack *tracks;
    int i, res;

    res = ebml_parse(matroska, matroska_tracks, matroska, MATROSKA_ID_TRACKS, 0);

    tracks = matroska->tracks.elem;
    for (i=0; i<matroska->tracks.nb_elem; i++) {
        MatroskaTrack *track = &tracks[i];
        EbmlList *encodings_list = &tracks->encodings;
        MatroskaTrackEncoding *encodings = encodings_list->elem;

        if (track->type != MATROSKA_TRACK_TYPE_VIDEO &&
            track->type != MATROSKA_TRACK_TYPE_AUDIO &&
            track->type != MATROSKA_TRACK_TYPE_SUBTITLE) {
            av_log(matroska->ctx, AV_LOG_INFO,
                   "Unknown or unsupported track type %"PRIu64"\n",
                   track->type);
            continue;
        }

        if (track->type == MATROSKA_TRACK_TYPE_VIDEO) {
            if (!track->default_duration)
                track->default_duration = 1000000000/track->video.frame_rate;
            if (!track->video.display_width)
                track->video.display_width = track->video.pixel_width;
            if (!track->video.display_height)
                track->video.display_height = track->video.pixel_height;
        } else if (track->type == MATROSKA_TRACK_TYPE_AUDIO) {
            if (!track->audio.out_samplerate)
                track->audio.out_samplerate = track->audio.samplerate;
        }
        if (encodings_list->nb_elem > 1) {
            av_log(matroska->ctx, AV_LOG_ERROR,
                   "Multiple combined encodings no supported");
        } else if (encodings_list->nb_elem == 1) {
            if (encodings[0].type ||
                (encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_HEADERSTRIP &&
#ifdef CONFIG_ZLIB
                 encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_ZLIB &&
#endif
#ifdef CONFIG_BZLIB
                 encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_BZLIB &&
#endif
                 encodings[0].compression.algo != MATROSKA_TRACK_ENCODING_COMP_LZO)) {
                encodings[0].scope = 0;
                av_log(matroska->ctx, AV_LOG_ERROR,
                       "Unsupported encoding type");
            } else if (track->codec_priv.size && encodings[0].scope&2) {
                uint8_t *codec_priv = track->codec_priv.data;
                int offset = matroska_decode_buffer(&track->codec_priv.data,
                                                    &track->codec_priv.size,
                                                    track);
                if (offset < 0) {
                    track->codec_priv.data = NULL;
                    track->codec_priv.size = 0;
                    av_log(matroska->ctx, AV_LOG_ERROR,
                           "Failed to decode codec private data\n");
                } else if (offset > 0) {
                    track->codec_priv.data = av_malloc(track->codec_priv.size + offset);
                    memcpy(track->codec_priv.data,
                           encodings[0].compression.settings.data, offset);
                    memcpy(track->codec_priv.data+offset, codec_priv,
                           track->codec_priv.size);
                    track->codec_priv.size += offset;
                }
                if (codec_priv != track->codec_priv.data)
                    av_free(codec_priv);
            }
        }
    }

    return res;
}

static int
matroska_parse_index (MatroskaDemuxContext *matroska)
{
    return ebml_parse(matroska, matroska_index, matroska, MATROSKA_ID_CUES, 0);
}

static int
matroska_parse_metadata (MatroskaDemuxContext *matroska)
{
    return ebml_parse(matroska, matroska_tags, matroska, MATROSKA_ID_TAGS, 0);
}

static int
matroska_parse_seekhead (MatroskaDemuxContext *matroska)
{
    return ebml_parse(matroska, matroska_seekhead, matroska, MATROSKA_ID_SEEKHEAD, 0);
}

static void
matroska_execute_seekhead(MatroskaDemuxContext *matroska)
{
    EbmlList *seekhead_list = &matroska->seekhead;
    MatroskaSeekhead *seekhead = seekhead_list->elem;
    uint32_t peek_id_cache = matroska->peek_id;
    uint32_t level_up = matroska->level_up;
    offset_t before_pos = url_ftell(matroska->ctx->pb);
    MatroskaLevel level;
    uint32_t id;
    int i, res;

    for (i=0; i<seekhead_list->nb_elem; i++) {
        if (seekhead[i].pos <= before_pos
            || seekhead[i].id == MATROSKA_ID_SEEKHEAD
            || seekhead[i].id == MATROSKA_ID_CLUSTER)
            continue;

        /* seek */
        if (ebml_read_seek(matroska,
                           seekhead[i].pos+matroska->segment_start) < 0)
            continue;

        /* we don't want to lose our seekhead level, so we add
         * a dummy. This is a crude hack. */
        if (matroska->num_levels == EBML_MAX_DEPTH) {
            av_log(matroska->ctx, AV_LOG_INFO,
                   "Max EBML element depth (%d) reached, "
                   "cannot parse further.\n", EBML_MAX_DEPTH);
            break;
        }

        level.start = 0;
        level.length = (uint64_t)-1;
        matroska->levels[matroska->num_levels] = level;
        matroska->num_levels++;

        /* check ID */
        if (!(id = ebml_peek_id (matroska,
                                 &matroska->level_up)))
            goto finish;
        if (id != seekhead[i].id) {
            av_log(matroska->ctx, AV_LOG_INFO,
                   "We looked for ID=0x%x but got "
                   "ID=0x%x (pos=%"PRIu64")",
                   (int)seekhead[i].id, id, seekhead[i].pos +
                   matroska->segment_start);
            goto finish;
        }

        /* read master + parse */
        switch (id) {
        case MATROSKA_ID_CUES:
            if (!(res = matroska_parse_index(matroska)) ||
                url_feof(matroska->ctx->pb)) {
                matroska->index_parsed = 1;
                res = 0;
            }
            break;
        case MATROSKA_ID_TAGS:
            if (!(res = matroska_parse_metadata(matroska)) ||
                url_feof(matroska->ctx->pb)) {
                matroska->metadata_parsed = 1;
                res = 0;
            }
            break;
        }

    finish:
        /* remove dummy level */
        while (matroska->num_levels) {
            uint64_t length = matroska->levels[--matroska->num_levels].length;
            if (length == (uint64_t)-1)
                break;
        }
    }

    /* seek back */
    ebml_read_seek(matroska, before_pos);
    matroska->peek_id = peek_id_cache;
    matroska->level_up = level_up;
}

static int
matroska_parse_attachments(AVFormatContext *s)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    EbmlList *attachements_list = &matroska->attachments;
    MatroskaAttachement *attachements;
    int i, j, res;

    res = ebml_parse(matroska, matroska_attachments, matroska, MATROSKA_ID_ATTACHMENTS, 0);

    attachements = attachements_list->elem;
    for (j=0; j<attachements_list->nb_elem; j++) {
        if (!(attachements[j].filename && attachements[j].mime &&
              attachements[j].bin.data && attachements[j].bin.size > 0)) {
            av_log(matroska->ctx, AV_LOG_ERROR, "incomplete attachment\n");
        } else {
            AVStream *st = av_new_stream(s, matroska->num_streams++);
            if (st == NULL)
                break;
            st->filename          = av_strdup(attachements[j].filename);
            st->codec->codec_id = CODEC_ID_NONE;
            st->codec->codec_type = CODEC_TYPE_ATTACHMENT;
            st->codec->extradata  = av_malloc(attachements[j].bin.size);
            if(st->codec->extradata == NULL)
                break;
            st->codec->extradata_size = attachements[j].bin.size;
            memcpy(st->codec->extradata, attachements[j].bin.data, attachements[j].bin.size);

            for (i=0; ff_mkv_mime_tags[i].id != CODEC_ID_NONE; i++) {
                if (!strncmp(ff_mkv_mime_tags[i].str, attachements[j].mime,
                             strlen(ff_mkv_mime_tags[i].str))) {
                    st->codec->codec_id = ff_mkv_mime_tags[i].id;
                    break;
                }
            }
        }
    }

    return res;
}

static int
matroska_parse_chapters(AVFormatContext *s)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    EbmlList *chapters_list = &matroska->chapters;
    MatroskaChapter *chapters;
    int i, res;

    res = ebml_parse(matroska, matroska_chapters, matroska, MATROSKA_ID_CHAPTERS, 0);

    chapters = chapters_list->elem;
    for (i=0; i<chapters_list->nb_elem; i++)
        if (chapters[i].start != AV_NOPTS_VALUE && chapters[i].uid)
            ff_new_chapter(s, chapters[i].uid, (AVRational){1, 1000000000},
                           chapters[i].start, chapters[i].end,
                           chapters[i].title);

    return res;
}

static int
matroska_aac_profile (char *codec_id)
{
    static const char *aac_profiles[] = {
        "MAIN", "LC", "SSR"
    };
    int profile;

    for (profile=0; profile<ARRAY_SIZE(aac_profiles); profile++)
        if (strstr(codec_id, aac_profiles[profile]))
            break;
    return profile + 1;
}

static int
matroska_aac_sri (int samplerate)
{
    int sri;

    for (sri=0; sri<ARRAY_SIZE(ff_mpeg4audio_sample_rates); sri++)
        if (ff_mpeg4audio_sample_rates[sri] == samplerate)
            break;
    return sri;
}

static int
matroska_read_header (AVFormatContext    *s,
                      AVFormatParameters *ap)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    MatroskaTrack *tracks;
    EbmlList *index_list;
    MatroskaIndex *index;
    int i, j, last_level, res = 0;
    Ebml ebml = { 0 };
    AVStream *st;
    uint32_t id;

    matroska->ctx = s;

    /* First read the EBML header. */
    if (ebml_parse(matroska, ebml_syntax, &ebml, 0, 1)
        || ebml.version > EBML_VERSION       || ebml.max_size > sizeof(uint64_t)
        || ebml.id_length > sizeof(uint32_t) || strcmp(ebml.doctype, "matroska")
        || ebml.doctype_version > 2) {
        av_log(matroska->ctx, AV_LOG_ERROR,
               "EBML header using unsupported features\n"
               "(EBML version %"PRIu64", doctype %s, doc version %"PRIu64")\n",
               ebml.version, ebml.doctype, ebml.doctype_version);
        return AVERROR_NOFMT;
    }
    ebml_free(ebml_syntax, &ebml);

    /* The next thing is a segment. */
    while (1) {
        if (!(id = ebml_peek_id(matroska, &last_level)))
            return AVERROR(EIO);
        if (id == MATROSKA_ID_SEGMENT)
            break;

        /* oi! */
        av_log(matroska->ctx, AV_LOG_INFO,
               "Expected a Segment ID (0x%x), but received 0x%x!\n",
               MATROSKA_ID_SEGMENT, id);
        if ((res = ebml_read_skip(matroska)) < 0)
            return res;
    }

    /* We now have a Matroska segment.
     * Seeks are from the beginning of the segment,
     * after the segment ID/length. */
    if ((res = ebml_read_master(matroska, &id)) < 0)
        return res;
    matroska->segment_start = url_ftell(s->pb);

    matroska->time_scale = 1000000;
    /* we've found our segment, start reading the different contents in here */
    while (res == 0) {
        if (!(id = ebml_peek_id(matroska, &matroska->level_up))) {
            res = AVERROR(EIO);
            break;
        } else if (matroska->level_up) {
            matroska->level_up--;
            break;
        }

        switch (id) {
            /* stream info */
            case MATROSKA_ID_INFO: {
                res = matroska_parse_info(matroska);
                break;
            }

            /* track info headers */
            case MATROSKA_ID_TRACKS: {
                res = matroska_parse_tracks(matroska);
                break;
            }

            /* stream index */
            case MATROSKA_ID_CUES: {
                if (!matroska->index_parsed) {
                    res = matroska_parse_index(matroska);
                } else
                    res = ebml_read_skip(matroska);
                break;
            }

            /* metadata */
            case MATROSKA_ID_TAGS: {
                if (!matroska->metadata_parsed) {
                    res = matroska_parse_metadata(matroska);
                } else
                    res = ebml_read_skip(matroska);
                break;
            }

            /* file index (if seekable, seek to Cues/Tags to parse it) */
            case MATROSKA_ID_SEEKHEAD: {
                res = matroska_parse_seekhead(matroska);
                break;
            }

            case MATROSKA_ID_ATTACHMENTS: {
                res = matroska_parse_attachments(s);
                break;
            }

            case MATROSKA_ID_CLUSTER: {
                /* Do not read the master - this will be done in the next
                 * call to matroska_read_packet. */
                res = 1;
                break;
            }

            case MATROSKA_ID_CHAPTERS: {
                res = matroska_parse_chapters(s);
                break;
            }

            default:
                av_log(matroska->ctx, AV_LOG_INFO,
                       "Unknown matroska file header ID 0x%x\n", id);
            /* fall-through */

            case EBML_ID_VOID:
                res = ebml_read_skip(matroska);
                break;
        }

        if (matroska->level_up) {
            matroska->level_up--;
            break;
        }
    }
    matroska_execute_seekhead(matroska);

    /* Have we found a cluster? */
    if (ebml_peek_id(matroska, NULL) != MATROSKA_ID_CLUSTER)
        return -1;

    {
        tracks = matroska->tracks.elem;
        for (i=0; i < matroska->tracks.nb_elem; i++) {
            MatroskaTrack *track = &tracks[i];
            enum CodecID codec_id = CODEC_ID_NONE;
            uint8_t *extradata = NULL;
            int extradata_size = 0;
            int extradata_offset = 0;

            /* Apply some sanity checks. */
            if (track->codec_id == NULL)
                continue;

            for(j=0; ff_mkv_codec_tags[j].id != CODEC_ID_NONE; j++){
                if(!strncmp(ff_mkv_codec_tags[j].str, track->codec_id,
                            strlen(ff_mkv_codec_tags[j].str))){
                    codec_id= ff_mkv_codec_tags[j].id;
                    break;
                }
            }

            st = track->stream = av_new_stream(s, matroska->num_streams++);
            if (st == NULL)
                return AVERROR(ENOMEM);

            /* Set the FourCC from the CodecID. */
            /* This is the MS compatibility mode which stores a
             * BITMAPINFOHEADER in the CodecPrivate. */
            if (!strcmp(track->codec_id,
                        MATROSKA_CODEC_ID_VIDEO_VFW_FOURCC) &&
                (track->codec_priv.size >= 40) &&
                (track->codec_priv.data != NULL)) {
                /* Offset of biCompression. Stored in LE. */
                track->video.fourcc = AV_RL32(track->codec_priv.data + 16);
                codec_id = codec_get_id(codec_bmp_tags, track->video.fourcc);

            }

            /* This is the MS compatibility mode which stores a
             * WAVEFORMATEX in the CodecPrivate. */
            else if (!strcmp(track->codec_id,
                             MATROSKA_CODEC_ID_AUDIO_ACM) &&
                (track->codec_priv.size >= 18) &&
                (track->codec_priv.data != NULL)) {
                /* Offset of wFormatTag. Stored in LE. */
                uint16_t tag = AV_RL16(track->codec_priv.data);
                codec_id = codec_get_id(codec_wav_tags, tag);

            }

            if (!strcmp(track->codec_id, "V_QUICKTIME") &&
                (track->codec_priv.size >= 86) &&
                (track->codec_priv.data != NULL)) {
                track->video.fourcc = AV_RL32(track->codec_priv.data);
                codec_id=codec_get_id(codec_movvideo_tags, track->video.fourcc);
            }

            else if (codec_id == CODEC_ID_AAC && !track->codec_priv.size) {
                int profile = matroska_aac_profile(track->codec_id);
                int sri = matroska_aac_sri(track->audio.samplerate);
                extradata = av_malloc(5);
                if (extradata == NULL)
                    return AVERROR(ENOMEM);
                extradata[0] = (profile << 3) | ((sri&0x0E) >> 1);
                extradata[1] = ((sri&0x01) << 7) | (track->audio.channels<<3);
                if (strstr(track->codec_id, "SBR")) {
                    sri = matroska_aac_sri(track->audio.out_samplerate);
                    extradata[2] = 0x56;
                    extradata[3] = 0xE5;
                    extradata[4] = 0x80 | (sri<<3);
                    extradata_size = 5;
                } else {
                    extradata_size = 2;
                }
            }

            else if (codec_id == CODEC_ID_TTA) {
                ByteIOContext b;
                extradata_size = 30;
                extradata = av_mallocz(extradata_size);
                if (extradata == NULL)
                    return AVERROR(ENOMEM);
                init_put_byte(&b, extradata, extradata_size, 1,
                              NULL, NULL, NULL, NULL);
                put_buffer(&b, "TTA1", 4);
                put_le16(&b, 1);
                put_le16(&b, track->audio.channels);
                put_le16(&b, track->audio.bitdepth);
                put_le32(&b, track->audio.out_samplerate);
                put_le32(&b, matroska->ctx->duration * track->audio.out_samplerate);
            }

            else if (codec_id == CODEC_ID_RV10 || codec_id == CODEC_ID_RV20 ||
                     codec_id == CODEC_ID_RV30 || codec_id == CODEC_ID_RV40) {
                extradata_offset = 26;
                track->codec_priv.size -= extradata_offset;
            }

            else if (codec_id == CODEC_ID_RA_144) {
                track->audio.out_samplerate = 8000;
                track->audio.channels = 1;
            }

            else if (codec_id == CODEC_ID_RA_288 ||
                     codec_id == CODEC_ID_COOK ||
                     codec_id == CODEC_ID_ATRAC3) {
                ByteIOContext b;

                init_put_byte(&b, track->codec_priv.data,track->codec_priv.size,
                              0, NULL, NULL, NULL, NULL);
                url_fskip(&b, 24);
                track->audio.coded_framesize = get_be32(&b);
                url_fskip(&b, 12);
                track->audio.sub_packet_h    = get_be16(&b);
                track->audio.frame_size      = get_be16(&b);
                track->audio.sub_packet_size = get_be16(&b);
                track->audio.buf = av_malloc(track->audio.frame_size * track->audio.sub_packet_h);
                if (codec_id == CODEC_ID_RA_288) {
                    st->codec->block_align = track->audio.coded_framesize;
                    track->codec_priv.size = 0;
                } else {
                    st->codec->block_align = track->audio.sub_packet_size;
                    extradata_offset = 78;
                    track->codec_priv.size -= extradata_offset;
                }
            }

            if (codec_id == CODEC_ID_NONE) {
                av_log(matroska->ctx, AV_LOG_INFO,
                       "Unknown/unsupported CodecID %s.\n",
                       track->codec_id);
            }

            av_set_pts_info(st, 64, matroska->time_scale*track->time_scale, 1000*1000*1000); /* 64 bit pts in ns */

            st->codec->codec_id = codec_id;
            st->start_time = 0;
            if (strcmp(track->language, "und"))
                av_strlcpy(st->language, track->language, 4);

            if (track->flag_default)
                st->disposition |= AV_DISPOSITION_DEFAULT;

            if (track->default_duration)
                av_reduce(&st->codec->time_base.num, &st->codec->time_base.den,
                          track->default_duration, 1000000000, 30000);

            if(extradata){
                st->codec->extradata = extradata;
                st->codec->extradata_size = extradata_size;
            } else if(track->codec_priv.data && track->codec_priv.size > 0){
                st->codec->extradata = av_malloc(track->codec_priv.size);
                if(st->codec->extradata == NULL)
                    return AVERROR(ENOMEM);
                st->codec->extradata_size = track->codec_priv.size;
                memcpy(st->codec->extradata,
                       track->codec_priv.data + extradata_offset,
                       track->codec_priv.size);
            }

            if (track->type == MATROSKA_TRACK_TYPE_VIDEO) {
                st->codec->codec_type = CODEC_TYPE_VIDEO;
                st->codec->codec_tag  = track->video.fourcc;
                st->codec->width  = track->video.pixel_width;
                st->codec->height = track->video.pixel_height;
                av_reduce(&st->codec->sample_aspect_ratio.num,
                          &st->codec->sample_aspect_ratio.den,
                          st->codec->height * track->video.display_width,
                          st->codec-> width * track->video.display_height,
                          255);
                st->need_parsing = AVSTREAM_PARSE_HEADERS;
            } else if (track->type == MATROSKA_TRACK_TYPE_AUDIO) {
                st->codec->codec_type = CODEC_TYPE_AUDIO;
                st->codec->sample_rate = track->audio.out_samplerate;
                st->codec->channels = track->audio.channels;
            } else if (track->type == MATROSKA_TRACK_TYPE_SUBTITLE) {
                st->codec->codec_type = CODEC_TYPE_SUBTITLE;
            }

            /* What do we do with private data? E.g. for Vorbis. */
        }
        res = 0;
    }

    index_list = &matroska->index;
    index = index_list->elem;
    for (i=0; i<index_list->nb_elem; i++) {
        EbmlList *pos_list = &index[i].pos;
        MatroskaIndexPos *pos = pos_list->elem;
        for (j=0; j<pos_list->nb_elem; j++) {
            MatroskaTrack *track = matroska_find_track_by_num(matroska,
                                                              pos[j].track);
            if (track && track->stream)
                av_add_index_entry(track->stream,
                                   pos[j].pos + matroska->segment_start,
                                   index[i].time*matroska->time_scale/AV_TIME_BASE,
                                   0, 0, AVINDEX_KEYFRAME);
        }
    }

    return res;
}

static int
matroska_parse_block(MatroskaDemuxContext *matroska, uint8_t *data, int size,
                     int64_t pos, uint64_t cluster_time, uint64_t duration,
                     int is_keyframe)
{
    MatroskaTrack *track;
    int res = 0;
    AVStream *st;
    AVPacket *pkt;
    uint8_t *origdata = data;
    int16_t block_time;
    uint32_t *lace_size = NULL;
    int n, flags, laces = 0;
    uint64_t num;

    /* first byte(s): tracknum */
    if ((n = matroska_ebmlnum_uint(data, size, &num)) < 0) {
        av_log(matroska->ctx, AV_LOG_ERROR, "EBML block data error\n");
        av_free(origdata);
        return res;
    }
    data += n;
    size -= n;

    /* fetch track from num */
    track = matroska_find_track_by_num(matroska, num);
    if (size <= 3 || !track || !track->stream) {
        av_log(matroska->ctx, AV_LOG_INFO,
               "Invalid stream %"PRIu64" or size %u\n", num, size);
        av_free(origdata);
        return res;
    }
    st = track->stream;
    if (st->discard >= AVDISCARD_ALL) {
        av_free(origdata);
        return res;
    }
    if (duration == AV_NOPTS_VALUE)
        duration = track->default_duration / matroska->time_scale;

    /* block_time (relative to cluster time) */
    block_time = AV_RB16(data);
    data += 2;
    flags = *data++;
    size -= 3;
    if (is_keyframe == -1)
        is_keyframe = flags & 0x80 ? PKT_FLAG_KEY : 0;

    if (matroska->skip_to_keyframe) {
        if (!is_keyframe || st != matroska->skip_to_stream) {
            av_free(origdata);
            return res;
        }
        matroska->skip_to_keyframe = 0;
    }

    switch ((flags & 0x06) >> 1) {
        case 0x0: /* no lacing */
            laces = 1;
            lace_size = av_mallocz(sizeof(int));
            lace_size[0] = size;
            break;

        case 0x1: /* xiph lacing */
        case 0x2: /* fixed-size lacing */
        case 0x3: /* EBML lacing */
            assert(size>0); // size <=3 is checked before size-=3 above
            laces = (*data) + 1;
            data += 1;
            size -= 1;
            lace_size = av_mallocz(laces * sizeof(int));

            switch ((flags & 0x06) >> 1) {
                case 0x1: /* xiph lacing */ {
                    uint8_t temp;
                    uint32_t total = 0;
                    for (n = 0; res == 0 && n < laces - 1; n++) {
                        while (1) {
                            if (size == 0) {
                                res = -1;
                                break;
                            }
                            temp = *data;
                            lace_size[n] += temp;
                            data += 1;
                            size -= 1;
                            if (temp != 0xff)
                                break;
                        }
                        total += lace_size[n];
                    }
                    lace_size[n] = size - total;
                    break;
                }

                case 0x2: /* fixed-size lacing */
                    for (n = 0; n < laces; n++)
                        lace_size[n] = size / laces;
                    break;

                case 0x3: /* EBML lacing */ {
                    uint32_t total;
                    n = matroska_ebmlnum_uint(data, size, &num);
                    if (n < 0) {
                        av_log(matroska->ctx, AV_LOG_INFO,
                               "EBML block data error\n");
                        break;
                    }
                    data += n;
                    size -= n;
                    total = lace_size[0] = num;
                    for (n = 1; res == 0 && n < laces - 1; n++) {
                        int64_t snum;
                        int r;
                        r = matroska_ebmlnum_sint (data, size, &snum);
                        if (r < 0) {
                            av_log(matroska->ctx, AV_LOG_INFO,
                                   "EBML block data error\n");
                            break;
                        }
                        data += r;
                        size -= r;
                        lace_size[n] = lace_size[n - 1] + snum;
                        total += lace_size[n];
                    }
                    lace_size[n] = size - total;
                    break;
                }
            }
            break;
    }

    if (res == 0) {
        uint64_t timecode = AV_NOPTS_VALUE;

        if (cluster_time != (uint64_t)-1
            && (block_time >= 0 || cluster_time >= -block_time))
            timecode = cluster_time + block_time;

        for (n = 0; n < laces; n++) {
            if (st->codec->codec_id == CODEC_ID_RA_288 ||
                st->codec->codec_id == CODEC_ID_COOK ||
                st->codec->codec_id == CODEC_ID_ATRAC3) {
                int a = st->codec->block_align;
                int sps = track->audio.sub_packet_size;
                int cfs = track->audio.coded_framesize;
                int h = track->audio.sub_packet_h;
                int y = track->audio.sub_packet_cnt;
                int w = track->audio.frame_size;
                int x;

                if (!track->audio.pkt_cnt) {
                    if (st->codec->codec_id == CODEC_ID_RA_288)
                        for (x=0; x<h/2; x++)
                            memcpy(track->audio.buf+x*2*w+y*cfs,
                                   data+x*cfs, cfs);
                    else
                        for (x=0; x<w/sps; x++)
                            memcpy(track->audio.buf+sps*(h*x+((h+1)/2)*(y&1)+(y>>1)), data+x*sps, sps);

                    if (++track->audio.sub_packet_cnt >= h) {
                        track->audio.sub_packet_cnt = 0;
                        track->audio.pkt_cnt = h*w / a;
                    }
                }
                while (track->audio.pkt_cnt) {
                    pkt = av_mallocz(sizeof(AVPacket));
                    av_new_packet(pkt, a);
                    memcpy(pkt->data, track->audio.buf
                           + a * (h*w / a - track->audio.pkt_cnt--), a);
                    pkt->pos = pos;
                    pkt->stream_index = st->index;
                    matroska_queue_packet(matroska, pkt);
                }
            } else {
                MatroskaTrackEncoding *encodings = track->encodings.elem;
                int offset = 0, pkt_size = lace_size[n];
                uint8_t *pkt_data = data;

                if (encodings && encodings->scope & 1) {
                    offset = matroska_decode_buffer(&pkt_data, &pkt_size,
                                                    track);
                    if (offset < 0)
                        continue;
                }

                pkt = av_mallocz(sizeof(AVPacket));
                /* XXX: prevent data copy... */
                if (av_new_packet(pkt, pkt_size+offset) < 0) {
                    av_free(pkt);
                    res = AVERROR(ENOMEM);
                    n = laces-1;
                    break;
                }
                if (offset)
                    memcpy (pkt->data, encodings->compression.settings.data, offset);
                memcpy (pkt->data+offset, pkt_data, pkt_size);

                if (pkt_data != data)
                    av_free(pkt_data);

                if (n == 0)
                    pkt->flags = is_keyframe;
                pkt->stream_index = st->index;

                pkt->pts = timecode;
                pkt->pos = pos;
                pkt->duration = duration;

                matroska_queue_packet(matroska, pkt);
            }

            if (timecode != AV_NOPTS_VALUE)
                timecode = duration ? timecode + duration : AV_NOPTS_VALUE;
            data += lace_size[n];
        }
    }

    av_free(lace_size);
    av_free(origdata);
    return res;
}

static int
matroska_parse_blockgroup (MatroskaDemuxContext *matroska,
                           uint64_t              cluster_time)
{
    int res = 0;
    uint32_t id;
    int is_keyframe = PKT_FLAG_KEY, last_num_packets = matroska->num_packets;
    uint64_t duration = AV_NOPTS_VALUE;
    uint8_t *data;
    int size = 0;
    int64_t pos = 0;

    av_log(matroska->ctx, AV_LOG_DEBUG, "parsing blockgroup...\n");

    while (res == 0) {
        if (!(id = ebml_peek_id(matroska, &matroska->level_up))) {
            res = AVERROR(EIO);
            break;
        } else if (matroska->level_up) {
            matroska->level_up--;
            break;
        }

        switch (id) {
            /* one block inside the group. Note, block parsing is one
             * of the harder things, so this code is a bit complicated.
             * See http://www.matroska.org/ for documentation. */
            case MATROSKA_ID_BLOCK: {
                pos = url_ftell(matroska->ctx->pb);
                res = ebml_read_binary(matroska, &id, &data, &size);
                break;
            }

            case MATROSKA_ID_BLOCKDURATION: {
                if ((res = ebml_read_uint(matroska, &id, &duration)) < 0)
                    break;
                break;
            }

            case MATROSKA_ID_BLOCKREFERENCE: {
                int64_t num;
                /* We've found a reference, so not even the first frame in
                 * the lace is a key frame. */
                is_keyframe = 0;
                if (last_num_packets != matroska->num_packets)
                    matroska->packets[last_num_packets]->flags = 0;
                if ((res = ebml_read_sint(matroska, &id, &num)) < 0)
                    break;
                break;
            }

            default:
                av_log(matroska->ctx, AV_LOG_INFO,
                       "Unknown entry 0x%x in blockgroup data\n", id);
                /* fall-through */

            case EBML_ID_VOID:
                res = ebml_read_skip(matroska);
                break;
        }

        if (matroska->level_up) {
            matroska->level_up--;
            break;
        }
    }

    if (res)
        return res;

    if (size > 0)
        res = matroska_parse_block(matroska, data, size, pos, cluster_time,
                                   duration, is_keyframe);

    return res;
}

static int
matroska_parse_cluster (MatroskaDemuxContext *matroska)
{
    int res = 0;
    uint32_t id;
    uint64_t cluster_time = 0;
    uint8_t *data;
    int64_t pos;
    int size;

    av_log(matroska->ctx, AV_LOG_DEBUG,
           "parsing cluster at %"PRId64"\n", url_ftell(matroska->ctx->pb));

    while (res == 0) {
        if (!(id = ebml_peek_id(matroska, &matroska->level_up))) {
            res = AVERROR(EIO);
            break;
        } else if (matroska->level_up) {
            matroska->level_up--;
            break;
        }

        switch (id) {
            /* cluster timecode */
            case MATROSKA_ID_CLUSTERTIMECODE: {
                uint64_t num;
                if ((res = ebml_read_uint(matroska, &id, &num)) < 0)
                    break;
                cluster_time = num;
                break;
            }

                /* a group of blocks inside a cluster */
            case MATROSKA_ID_BLOCKGROUP:
                if ((res = ebml_read_master(matroska, &id)) < 0)
                    break;
                res = matroska_parse_blockgroup(matroska, cluster_time);
                break;

            case MATROSKA_ID_SIMPLEBLOCK:
                pos = url_ftell(matroska->ctx->pb);
                res = ebml_read_binary(matroska, &id, &data, &size);
                if (res == 0)
                    res = matroska_parse_block(matroska, data, size, pos,
                                               cluster_time, AV_NOPTS_VALUE,
                                               -1);
                break;

            default:
                av_log(matroska->ctx, AV_LOG_INFO,
                       "Unknown entry 0x%x in cluster data\n", id);
                /* fall-through */

            case EBML_ID_VOID:
                res = ebml_read_skip(matroska);
                break;
        }

        if (matroska->level_up) {
            matroska->level_up--;
            break;
        }
    }

    return res;
}

static int
matroska_read_packet (AVFormatContext *s,
                      AVPacket        *pkt)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    int res;
    uint32_t id;

    /* Read stream until we have a packet queued. */
    while (matroska_deliver_packet(matroska, pkt)) {

        /* Have we already reached the end? */
        if (matroska->done)
            return AVERROR(EIO);

        res = 0;
        while (res == 0) {
            if (!(id = ebml_peek_id(matroska, &matroska->level_up))) {
                return AVERROR(EIO);
            } else if (matroska->level_up) {
                matroska->level_up--;
                break;
            }

            switch (id) {
                case MATROSKA_ID_CLUSTER:
                    if ((res = ebml_read_master(matroska, &id)) < 0)
                        break;
                    if ((res = matroska_parse_cluster(matroska)) == 0)
                        res = 1; /* Parsed one cluster, let's get out. */
                    break;

                default:
                case EBML_ID_VOID:
                    res = ebml_read_skip(matroska);
                    break;
            }

            if (matroska->level_up) {
                matroska->level_up--;
                break;
            }
        }

        if (res == -1)
            matroska->done = 1;
    }

    return 0;
}

static int
matroska_read_seek (AVFormatContext *s, int stream_index, int64_t timestamp,
                    int flags)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    AVStream *st = s->streams[stream_index];
    int index;

    /* find index entry */
    index = av_index_search_timestamp(st, timestamp, flags);
    if (index < 0)
        return 0;

    matroska_clear_queue(matroska);

    /* do the seek */
    url_fseek(s->pb, st->index_entries[index].pos, SEEK_SET);
    matroska->skip_to_keyframe = !(flags & AVSEEK_FLAG_ANY);
    matroska->skip_to_stream = st;
    matroska->peek_id = 0;
    av_update_cur_dts(s, st, st->index_entries[index].timestamp);
    return 0;
}

static int
matroska_read_close (AVFormatContext *s)
{
    MatroskaDemuxContext *matroska = s->priv_data;
    MatroskaTrack *tracks = matroska->tracks.elem;
    int n = 0;

    matroska_clear_queue(matroska);

    for (n=0; n < matroska->tracks.nb_elem; n++)
        if (tracks[n].type == MATROSKA_TRACK_TYPE_AUDIO)
            av_free(tracks[n].audio.buf);
    ebml_free(matroska_tracks, matroska);
    ebml_free(matroska_index, matroska);

    return 0;
}

AVInputFormat matroska_demuxer = {
    "matroska",
    NULL_IF_CONFIG_SMALL("Matroska file format"),
    sizeof(MatroskaDemuxContext),
    matroska_probe,
    matroska_read_header,
    matroska_read_packet,
    matroska_read_close,
    matroska_read_seek,
};