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WebM muxer writes WebVTT subtitle track

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The Matroska muxer now allows WebVTT subtitle tracks to be written
while in WebM muxing mode.

WebVTT subtitle tracks have four kinds: "subtitles", "captions",
"descriptions", and "metadata". Each text track kind has a distinct
Mastroska CodecID and track type, as described in the temporal
metadata guidelines here:

http://wiki.webmproject.org/webm-metadata/temporal-metadata/webvtt-in-webm

When the stream has codec id AV_CODEC_ID_WEBVTT, the stream packet is
serialized per the temporal metadata guidelines cited above. The
WebVTT cue is written as a Matroska block group. The block frame
comprises the WebVTT cue id, followed by the cue settings, followed by
the cue text.  (The block timestamp is synthesized from the cue
timestamp.)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
pull/27/head
Matthew Heaney 12 years ago committed by Michael Niedermayer
parent a20f049c2a
commit 509642b4bd
2 changed files with 85 additions and 13 deletions
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  1. 1
      libavformat/matroska.h
  2. 97
      libavformat/matroskaenc.c

1
libavformat/matroska.h
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@ -230,6 +230,7 @@ typedef enum {
MATROSKA_TRACK_TYPE_LOGO = 0x10,
MATROSKA_TRACK_TYPE_SUBTITLE = 0x11,
MATROSKA_TRACK_TYPE_CONTROL = 0x20,
MATROSKA_TRACK_TYPE_METADATA = 0x21,
} MatroskaTrackType;
typedef enum {

97
libavformat/matroskaenc.c
Unescape View File

@ -600,7 +600,11 @@ static int mkv_write_tracks(AVFormatContext *s)
if ((tag = av_dict_get(st->metadata, "title", NULL, 0)))
put_ebml_string(pb, MATROSKA_ID_TRACKNAME, tag->value);
tag = av_dict_get(st->metadata, "language", NULL, 0);
put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag ? tag->value:"und");
if (mkv->mode != MODE_WEBM || codec->codec_id != AV_CODEC_ID_WEBVTT) {
put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag ? tag->value:"und");
} else if (tag && tag->value) {
put_ebml_string(pb, MATROSKA_ID_TRACKLANGUAGE, tag->value);
}
if (default_stream_exists) {
put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGDEFAULT, !!(st->disposition & AV_DISPOSITION_DEFAULT));
@ -608,22 +612,41 @@ static int mkv_write_tracks(AVFormatContext *s)
if (st->disposition & AV_DISPOSITION_FORCED)
put_ebml_uint(pb, MATROSKA_ID_TRACKFLAGFORCED, 1);
// look for a codec ID string specific to mkv to use,
// if none are found, use AVI codes
for (j = 0; ff_mkv_codec_tags[j].id != AV_CODEC_ID_NONE; j++) {
if (ff_mkv_codec_tags[j].id == codec->codec_id) {
put_ebml_string(pb, MATROSKA_ID_CODECID, ff_mkv_codec_tags[j].str);
native_id = 1;
break;
if (mkv->mode == MODE_WEBM && codec->codec_id == AV_CODEC_ID_WEBVTT) {
const char *codec_id;
if (st->disposition & AV_DISPOSITION_CAPTIONS) {
codec_id = "D_WEBVTT/CAPTIONS";
native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
} else if (st->disposition & AV_DISPOSITION_DESCRIPTIONS) {
codec_id = "D_WEBVTT/DESCRIPTIONS";
native_id = MATROSKA_TRACK_TYPE_METADATA;
} else if (st->disposition & AV_DISPOSITION_METADATA) {
codec_id = "D_WEBVTT/METADATA";
native_id = MATROSKA_TRACK_TYPE_METADATA;
} else {
codec_id = "D_WEBVTT/SUBTITLES";
native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
}
put_ebml_string(pb, MATROSKA_ID_CODECID, codec_id);
} else {
// look for a codec ID string specific to mkv to use,
// if none are found, use AVI codes
for (j = 0; ff_mkv_codec_tags[j].id != AV_CODEC_ID_NONE; j++) {
if (ff_mkv_codec_tags[j].id == codec->codec_id) {
put_ebml_string(pb, MATROSKA_ID_CODECID, ff_mkv_codec_tags[j].str);
native_id = 1;
break;
}
}
}
if (mkv->mode == MODE_WEBM && !(codec->codec_id == AV_CODEC_ID_VP8 ||
codec->codec_id == AV_CODEC_ID_VP9 ||
((codec->codec_id == AV_CODEC_ID_OPUS)&&(codec->strict_std_compliance <= FF_COMPLIANCE_EXPERIMENTAL)) ||
codec->codec_id == AV_CODEC_ID_VORBIS)) {
codec->codec_id == AV_CODEC_ID_VORBIS ||
codec->codec_id == AV_CODEC_ID_WEBVTT)) {
av_log(s, AV_LOG_ERROR,
"Only VP8,VP9 video and Vorbis,Opus(experimental, use -strict -2) audio are supported for WebM.\n");
"Only VP8,VP9 video and Vorbis,Opus(experimental, use -strict -2) audio and WebVTT subtitles are supported for WebM.\n");
return AVERROR(EINVAL);
}
@ -717,18 +740,25 @@ static int mkv_write_tracks(AVFormatContext *s)
break;
case AVMEDIA_TYPE_SUBTITLE:
put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_SUBTITLE);
if (!native_id) {
av_log(s, AV_LOG_ERROR, "Subtitle codec %d is not supported.\n", codec->codec_id);
return AVERROR(ENOSYS);
}
if (mkv->mode != MODE_WEBM || codec->codec_id != AV_CODEC_ID_WEBVTT)
native_id = MATROSKA_TRACK_TYPE_SUBTITLE;
put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, native_id);
break;
default:
av_log(s, AV_LOG_ERROR, "Only audio, video, and subtitles are supported for Matroska.\n");
return AVERROR(EINVAL);
}
ret = mkv_write_codecprivate(s, pb, codec, native_id, qt_id);
if (ret < 0) return ret;
if (mkv->mode != MODE_WEBM || codec->codec_id != AV_CODEC_ID_WEBVTT) {
ret = mkv_write_codecprivate(s, pb, codec, native_id, qt_id);
if (ret < 0) return ret;
}
end_ebml_master(pb, track);
@ -1308,6 +1338,44 @@ static int mkv_write_srt_blocks(AVFormatContext *s, AVIOContext *pb, AVPacket *p
return duration;
}
static int mkv_write_vtt_blocks(AVFormatContext *s, AVIOContext *pb, AVPacket *pkt)
{
MatroskaMuxContext *mkv = s->priv_data;
ebml_master blockgroup;
int id_size, settings_size, size;
uint8_t *id, *settings;
int64_t ts = mkv->tracks[pkt->stream_index].write_dts ? pkt->dts : pkt->pts;
const int flags = 0;
id_size = 0;
id = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_IDENTIFIER,
&id_size);
settings_size = 0;
settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
&settings_size);
size = id_size + 1 + settings_size + 1 + pkt->size;
av_log(s, AV_LOG_DEBUG, "Writing block at offset %" PRIu64 ", size %d, "
"pts %" PRId64 ", dts %" PRId64 ", duration %d, flags %d\n",
avio_tell(pb), size, pkt->pts, pkt->dts, pkt->duration, flags);
blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, mkv_blockgroup_size(size));
put_ebml_id(pb, MATROSKA_ID_BLOCK);
put_ebml_num(pb, size+4, 0);
avio_w8(pb, 0x80 | (pkt->stream_index + 1)); // this assumes stream_index is less than 126
avio_wb16(pb, ts - mkv->cluster_pts);
avio_w8(pb, flags);
avio_printf(pb, "%.*s\n%.*s\n%.*s", id_size, id, settings_size, settings, pkt->size, pkt->data);
put_ebml_uint(pb, MATROSKA_ID_BLOCKDURATION, pkt->duration);
end_ebml_master(pb, blockgroup);
return pkt->duration;
}
static void mkv_flush_dynbuf(AVFormatContext *s)
{
MatroskaMuxContext *mkv = s->priv_data;
@ -1363,6 +1431,8 @@ static int mkv_write_packet_internal(AVFormatContext *s, AVPacket *pkt)
#endif
} else if (codec->codec_id == AV_CODEC_ID_SRT) {
duration = mkv_write_srt_blocks(s, pb, pkt);
} else if (codec->codec_id == AV_CODEC_ID_WEBVTT) {
duration = mkv_write_vtt_blocks(s, pb, pkt);
} else {
ebml_master blockgroup = start_ebml_master(pb, MATROSKA_ID_BLOCKGROUP, mkv_blockgroup_size(pkt->size));
/* For backward compatibility, prefer convergence_duration. */
@ -1606,6 +1676,7 @@ AVOutputFormat ff_webm_muxer = {
.priv_data_size = sizeof(MatroskaMuxContext),
.audio_codec = AV_CODEC_ID_VORBIS,
.video_codec = AV_CODEC_ID_VP8,
.subtitle_codec = AV_CODEC_ID_WEBVTT,
.write_header = mkv_write_header,
.write_packet = mkv_write_packet,
.write_trailer = mkv_write_trailer,

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