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avformat/matroskaenc: Don't open BlockGroup twice 

This would happen in case non-WebVTT-subtitles had BlockAdditional
or DiscardPadding side-data. Given that these are not accounted for
in the length of the outer BlockGroup (which is a quite sharp upper
bound) it is possible for the outer BlockGroup to use an insufficient
number of bytes which leads to an assert in end_ebml_master().

Fix this by not opening a second BlockGroup inside an already opened
BlockGroup.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-01-15 07:43:03 +01:00
parent ca16863549
commit 5e186f9693
1 changed files with 4 additions and 2 deletions
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6
libavformat/matroskaenc.c
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@ -2095,6 +2095,7 @@ static int mkv_write_block(AVFormatContext *s, AVIOContext *pb,
int64_t discard_padding = 0;
unsigned track_number = track->track_num;
ebml_master block_group, block_additions, block_more;
int blockgroup_already_opened = blockid == MATROSKA_ID_BLOCK;
ts += track->ts_offset;
@ -2141,7 +2142,7 @@ static int mkv_write_block(AVFormatContext *s, AVIOContext *pb,
side_data = av_packet_get_side_data(pkt,
AV_PKT_DATA_SKIP_SAMPLES,
&side_data_size);
if (side_data && side_data_size >= 10) {
if (side_data && side_data_size >= 10 && !blockgroup_already_opened) {
discard_padding = av_rescale_q(AV_RL32(side_data + 4),
(AVRational){1, par->sample_rate},
(AVRational){1, 1000000000});
@ -2152,7 +2153,8 @@ static int mkv_write_block(AVFormatContext *s, AVIOContext *pb,
&side_data_size);
if (side_data) {
// Only the Codec-specific BlockMore (id == 1) is currently supported.
if (side_data_size < 8 || (additional_id = AV_RB64(side_data)) != 1) {
if (side_data_size < 8 || (additional_id = AV_RB64(side_data)) != 1 ||
blockgroup_already_opened) {
side_data_size = 0;
} else {
side_data += 8;