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avformat/matroskadec: Get rid of cluster size field assumption

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The earlier code relied on the length of clusters always being coded on
eight bytes as was the behaviour of libavformat's Matroska muxer until
recently. But given that our own Matroska muxer now (and mkvmerge from
time immemorial) creates files that don't conform to this assumption,
it is high time to get rid of this assumption.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2019-05-17 00:29:49 +02:00 committed by James Almer
parent 70baf729b5
commit 36aceb6174
1 changed files with 9 additions and 6 deletions
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15
libavformat/matroskadec.c
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@ -3656,15 +3656,17 @@ static int webm_clusters_start_with_keyframe(AVFormatContext *s)
cluster_pos = s->streams[0]->index_entries[index].pos;
before_pos = avio_tell(s->pb);
while (1) {
int64_t cluster_id = 0, cluster_length = 0;
uint64_t cluster_id, cluster_length;
int read;
AVPacket *pkt;
avio_seek(s->pb, cluster_pos, SEEK_SET);
// read cluster id and length
ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
if (cluster_id != 0xF43B675) { // done with all clusters
read = ebml_read_num(matroska, matroska->ctx->pb, 4, &cluster_id);
if (read < 0 || cluster_id != 0xF43B675) // done with all clusters
break;
read = ebml_read_length(matroska, matroska->ctx->pb, &cluster_length);
if (read < 0)
break;
}
avio_seek(s->pb, cluster_pos, SEEK_SET);
matroska->current_id = 0;
matroska_clear_queue(matroska);
@ -3673,7 +3675,8 @@ static int webm_clusters_start_with_keyframe(AVFormatContext *s)
break;
}
pkt = &matroska->queue->pkt;
cluster_pos += cluster_length + 12; // 12 is the offset of the cluster id and length.
// 4 + read is the length of the cluster id and the cluster length field.
cluster_pos += 4 + read + cluster_length;
if (!(pkt->flags & AV_PKT_FLAG_KEY)) {
rv = 0;
break;