matroskadec: Demux support for SeekPreRoll and CodecDelay

Adds support for demuxing SeekPreRoll and CodecDelay container
elements.

Signed-off-by: Vignesh Venkatasubramanian <vigneshv@google.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/matroskadec.c

@@ -163,6 +163,8 @@ typedef struct {
     uint64_t default_duration;
     uint64_t flag_default;
     uint64_t flag_forced;
+    uint64_t codec_delay;
+    uint64_t seek_preroll;
     MatroskaTrackVideo video;
     MatroskaTrackAudio audio;
     MatroskaTrackOperation operation;
@@ -410,6 +412,8 @@ static EbmlSyntax matroska_track[] = {
     { MATROSKA_ID_TRACKOPERATION,       EBML_NEST, 0, offsetof(MatroskaTrack,operation), {.n=matroska_track_operation} },
     { MATROSKA_ID_TRACKCONTENTENCODINGS,EBML_NEST, 0, 0, {.n=matroska_track_encodings} },
     { MATROSKA_ID_TRACKMAXBLKADDID,     EBML_UINT, 0, offsetof(MatroskaTrack,max_block_additional_id) },
+    { MATROSKA_ID_CODECDELAY,           EBML_UINT, 0, offsetof(MatroskaTrack,codec_delay) },
+    { MATROSKA_ID_SEEKPREROLL,          EBML_UINT, 0, offsetof(MatroskaTrack,seek_preroll) },
     { MATROSKA_ID_TRACKFLAGENABLED,     EBML_NONE },
     { MATROSKA_ID_TRACKFLAGLACING,      EBML_NONE },
     { MATROSKA_ID_CODECNAME,            EBML_NONE },
@@ -1878,6 +1882,17 @@ static int matroska_read_header(AVFormatContext *s)
             st->codec->bits_per_coded_sample = track->audio.bitdepth;
             if (st->codec->codec_id != AV_CODEC_ID_AAC)
             st->need_parsing = AVSTREAM_PARSE_HEADERS;
+            if (track->codec_delay > 0) {
+                st->codec->delay = av_rescale_q(track->codec_delay,
+                                                (AVRational){1, 1000000000},
+                                                (AVRational){1, st->codec->sample_rate});
+            }
+            if (track->seek_preroll > 0) {
+                av_codec_set_seek_preroll(st->codec,
+                                          av_rescale_q(track->seek_preroll,
+                                                       (AVRational){1, 1000000000},
+                                                       (AVRational){1, st->codec->sample_rate}));
+            }
         } else if (codec_id == AV_CODEC_ID_WEBVTT) {
             st->codec->codec_type = AVMEDIA_TYPE_SUBTITLE;