FFmpeg/libavcodec/mpegaudio_parser.c

/*
 * MPEG Audio parser
 * Copyright (c) 2003 Fabrice Bellard
 * Copyright (c) 2003 Michael Niedermayer
 *
 * 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
 */

#include "parser.h"
#include "mpegaudio.h"
#include "mpegaudiodecheader.h"


typedef struct MpegAudioParseContext {
    uint8_t inbuf[MPA_MAX_CODED_FRAME_SIZE];    /* input buffer */
    uint8_t *inbuf_ptr;
    int frame_size;
    int free_format_frame_size;
    int free_format_next_header;
    uint32_t header;
    int header_count;
} MpegAudioParseContext;

#define MPA_HEADER_SIZE 4

/* header + layer + bitrate + freq + lsf/mpeg25 */
#undef SAME_HEADER_MASK /* mpegaudio.h defines different version */
#define SAME_HEADER_MASK \
   (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))

/* useful helper to get mpeg audio stream infos. Return -1 if error in
   header, otherwise the coded frame size in bytes */
int ff_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
{
    MPADecodeHeader s1, *s = &s1;

    if (ff_mpa_check_header(head) != 0)
        return -1;

    if (ff_mpegaudio_decode_header(s, head) != 0) {
        return -1;
    }

    switch(s->layer) {
    case 1:
        avctx->codec_id = CODEC_ID_MP1;
        *frame_size = 384;
        break;
    case 2:
        avctx->codec_id = CODEC_ID_MP2;
        *frame_size = 1152;
        break;
    default:
    case 3:
        avctx->codec_id = CODEC_ID_MP3;
        if (s->lsf)
            *frame_size = 576;
        else
            *frame_size = 1152;
        break;
    }

    *sample_rate = s->sample_rate;
    *channels = s->nb_channels;
    *bit_rate = s->bit_rate;
    avctx->sub_id = s->layer;
    return s->frame_size;
}

static av_cold int mpegaudio_parse_init(AVCodecParserContext *s1)
{
    MpegAudioParseContext *s = s1->priv_data;
    s->inbuf_ptr = s->inbuf;
    return 0;
}

static int mpegaudio_parse(AVCodecParserContext *s1,
                           AVCodecContext *avctx,
                           const uint8_t **poutbuf, int *poutbuf_size,
                           const uint8_t *buf, int buf_size)
{
    MpegAudioParseContext *s = s1->priv_data;
    int len, ret, sr, channels, bit_rate, frame_size;
    uint32_t header;
    const uint8_t *buf_ptr;

    *poutbuf = NULL;
    *poutbuf_size = 0;
    buf_ptr = buf;
    while (buf_size > 0) {
        len = s->inbuf_ptr - s->inbuf;
        if (s->frame_size == 0) {
            /* special case for next header for first frame in free
               format case (XXX: find a simpler method) */
            if (s->free_format_next_header != 0) {
                AV_WB32(s->inbuf, s->free_format_next_header);
                s->inbuf_ptr = s->inbuf + 4;
                s->free_format_next_header = 0;
                goto got_header;
            }
            /* no header seen : find one. We need at least MPA_HEADER_SIZE
               bytes to parse it */
            len = FFMIN(MPA_HEADER_SIZE - len, buf_size);
            if (len > 0) {
                memcpy(s->inbuf_ptr, buf_ptr, len);
                buf_ptr += len;
                buf_size -= len;
                s->inbuf_ptr += len;
            }
            if ((s->inbuf_ptr - s->inbuf) >= MPA_HEADER_SIZE) {
            got_header:
                header = AV_RB32(s->inbuf);

                ret = ff_mpa_decode_header(avctx, header, &sr, &channels, &frame_size, &bit_rate);
                if (ret < 0) {
                    s->header_count= -2;
                    /* no sync found : move by one byte (inefficient, but simple!) */
                    memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
                    s->inbuf_ptr--;
                    dprintf(avctx, "skip %x\n", header);
                    /* reset free format frame size to give a chance
                       to get a new bitrate */
                    s->free_format_frame_size = 0;
                } else {
                    if((header&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
                        s->header_count= -3;
                    s->header= header;
                    s->header_count++;
                    s->frame_size = ret;

#if 0
                    /* free format: prepare to compute frame size */
                    if (ff_mpegaudio_decode_header((MPADecodeHeader *)s, header) == 1) {
                        s->frame_size = -1;
                    }
#endif
                    if(s->header_count > 1){
                        avctx->sample_rate= sr;
                        avctx->channels   = channels;
                        avctx->frame_size = frame_size;
                        avctx->bit_rate   = bit_rate;
                    }
                }
            }
        } else
#if 0
        if (s->frame_size == -1) {
            /* free format : find next sync to compute frame size */
            len = MPA_MAX_CODED_FRAME_SIZE - len;
            if (len > buf_size)
                len = buf_size;
            if (len == 0) {
                /* frame too long: resync */
                s->frame_size = 0;
                memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
                s->inbuf_ptr--;
            } else {
                uint8_t *p, *pend;
                uint32_t header1;
                int padding;

                memcpy(s->inbuf_ptr, buf_ptr, len);
                /* check for header */
                p = s->inbuf_ptr - 3;
                pend = s->inbuf_ptr + len - 4;
                while (p <= pend) {
                    header = AV_RB32(p);
                    header1 = AV_RB32(s->inbuf);
                    /* check with high probability that we have a
                       valid header */
                    if ((header & SAME_HEADER_MASK) ==
                        (header1 & SAME_HEADER_MASK)) {
                        /* header found: update pointers */
                        len = (p + 4) - s->inbuf_ptr;
                        buf_ptr += len;
                        buf_size -= len;
                        s->inbuf_ptr = p;
                        /* compute frame size */
                        s->free_format_next_header = header;
                        s->free_format_frame_size = s->inbuf_ptr - s->inbuf;
                        padding = (header1 >> 9) & 1;
                        if (s->layer == 1)
                            s->free_format_frame_size -= padding * 4;
                        else
                            s->free_format_frame_size -= padding;
                        dprintf(avctx, "free frame size=%d padding=%d\n",
                                s->free_format_frame_size, padding);
                        ff_mpegaudio_decode_header((MPADecodeHeader *)s, header1);
                        goto next_data;
                    }
                    p++;
                }
                /* not found: simply increase pointers */
                buf_ptr += len;
                s->inbuf_ptr += len;
                buf_size -= len;
            }
        } else
#endif
        if (len < s->frame_size) {
            if (s->frame_size > MPA_MAX_CODED_FRAME_SIZE)
                s->frame_size = MPA_MAX_CODED_FRAME_SIZE;
            len = FFMIN(s->frame_size - len, buf_size);
            memcpy(s->inbuf_ptr, buf_ptr, len);
            buf_ptr += len;
            s->inbuf_ptr += len;
            buf_size -= len;
        }

        if(s->frame_size > 0 && buf_ptr - buf == s->inbuf_ptr - s->inbuf
           && buf_size + buf_ptr - buf >= s->frame_size){
            if(s->header_count > 0){
                *poutbuf = buf;
                *poutbuf_size = s->frame_size;
            }
            buf_ptr = buf + s->frame_size;
            s->inbuf_ptr = s->inbuf;
            s->frame_size = 0;
            break;
        }

        //    next_data:
        if (s->frame_size > 0 &&
            (s->inbuf_ptr - s->inbuf) >= s->frame_size) {
            if(s->header_count > 0){
                *poutbuf = s->inbuf;
                *poutbuf_size = s->inbuf_ptr - s->inbuf;
            }
            s->inbuf_ptr = s->inbuf;
            s->frame_size = 0;
            break;
        }
    }
    return buf_ptr - buf;
}


AVCodecParser mpegaudio_parser = {
    { CODEC_ID_MP1, CODEC_ID_MP2, CODEC_ID_MP3 },
    sizeof(MpegAudioParseContext),
    mpegaudio_parse_init,
    mpegaudio_parse,
    NULL,
};