[FFmpeg-devel] [PATCH] WebM muxer writes WebVTT subtitle track
Matthew Heaney
matthewjheaney at google.com
Mon Jun 3 22:16:32 CEST 2013
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
In ffmpeg, the WebVTT kind can be specified explicitly using the
-metadata option to specify a mapping from key "kind" to one of the
kind values listed above. The kind "subtitles" is the default if no
mapping is specified.
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.)
---
libavformat/matroskaenc.c | 145 ++++++++++++++++++++++++++++++++++++++++------
1 file changed, 127 insertions(+), 18 deletions(-)
diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
index 99d648d..77c9fbb 100644
--- a/libavformat/matroskaenc.c
+++ b/libavformat/matroskaenc.c
@@ -560,6 +560,41 @@ static int mkv_write_tracks(AVFormatContext *s)
ebml_master tracks;
int i, j, ret, default_stream_exists = 0;
+ for (i = 0; i < s->nb_streams; i++) {
+ AVStream *st = s->streams[i];
+ AVCodecContext *codec = st->codec;
+ AVDictionaryEntry *t;
+
+ if (mkv->mode != MODE_WEBM)
+ continue;
+
+ if (codec->codec_id == AV_CODEC_ID_VP8
+ || codec->codec_id == AV_CODEC_ID_VORBIS) {
+ continue;
+ }
+
+ if (codec->codec_id != AV_CODEC_ID_WEBVTT) {
+ av_log(s, AV_LOG_ERROR,
+ "Only VP8 video, Vorbis audio, and WebVTT subtitles are supported for WebM.\n");
+ return AVERROR(EINVAL);
+ }
+
+ t = av_dict_get(st->metadata, "kind", NULL, 0);
+
+ if (!t)
+ continue;
+
+ if (!av_strcasecmp(t->value, "subtitles")
+ || !av_strcasecmp(t->value, "captions")
+ || !av_strcasecmp(t->value, "descriptions")
+ || !av_strcasecmp(t->value, "metadata")) {
+ continue;
+ }
+
+ av_log(s, AV_LOG_ERROR, "Bad WebVTT kind specifier.\n");
+ return AVERROR(EINVAL);
+ }
+
ret = mkv_add_seekhead_entry(mkv->main_seekhead, MATROSKA_ID_TRACKS, avio_tell(pb));
if (ret < 0) return ret;
@@ -599,8 +634,13 @@ 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));
@@ -608,21 +648,37 @@ 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 *str;
+ tag = av_dict_get(st->metadata, "kind", NULL, 0);
+
+ if (!tag) {
+ str = "D_WEBVTT/SUBTITLES";
+ native_id = 0x11;
+ } else if (!av_strcasecmp(tag->value, "captions")) {
+ str = "D_WEBVTT/CAPTIONS";
+ native_id = 0x11;
+ } else if (!av_strcasecmp(tag->value, "descriptions")) {
+ str = "D_WEBVTT/DESCRIPTIONS";
+ native_id = 0x21;
+ } else if (!av_strcasecmp(tag->value, "metadata")) {
+ str = "D_WEBVTT/METADATA";
+ native_id = 0x21;
+ } else {
+ str = "D_WEBVTT/SUBTITLES";
+ native_id = 0x11;
+ }
+ put_ebml_string(pb, MATROSKA_ID_CODECID, str);
+ } 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_VORBIS)) {
- av_log(s, AV_LOG_ERROR,
- "Only VP8 video and Vorbis audio are supported for WebM.\n");
- return AVERROR(EINVAL);
}
switch (codec->codec_type) {
@@ -715,18 +771,27 @@ 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) {
+ put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, native_id);
+ } else {
+ put_ebml_uint(pb, MATROSKA_ID_TRACKTYPE, MATROSKA_TRACK_TYPE_SUBTITLE);
+ }
+
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);
@@ -1306,6 +1371,48 @@ 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;
+ const uint8_t EOL[] = "\n";
+
+ 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_write(pb, id, id_size);
+ avio_write(pb, EOL, 1);
+ avio_write(pb, settings, settings_size);
+ avio_write(pb, EOL, 1);
+ avio_write(pb, pkt->data, pkt->size);
+
+ 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;
@@ -1361,6 +1468,8 @@ 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. */
--
1.8.2.1
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