[FFmpeg-devel] [PATCH 1/2] avformat/matroskaenc: fix Tags master on seekable output if there are tags after the last stream duration

[Dave Rice]

> On Oct 7, 2016, at 10:30 AM, James Almer <jamrial at gmail.com> wrote:
> 
> On 10/7/2016 3:05 AM, James Almer wrote:
>> The dynamic AVIOContext would get closed pointing to the wrong position
>> in the buffer.
>> This is a regression since 650e17d88b63b5aca6e0a43483e89e64b0f7d2dd.
>> 
>> Signed-off-by: James Almer <jamrial at gmail.com>
>> ---
>> Example:
>> ./ffmpeg -i fate-samples/vorbis/vorbis_chapter_extension_demo.ogg -c:a copy -metadata:c key=value out.mka
>> 
>> The output is corrupt before this patch.
>> 
>> The refactoring isn't necessary per se, but it comes in handy for the next patch,
>> where attachments will not be treated as tracks anymore when writting tags.
>> 
>> libavformat/matroskaenc.c | 15 +++++++++------
>> 1 file changed, 9 insertions(+), 6 deletions(-)
>> 
>> diff --git a/libavformat/matroskaenc.c b/libavformat/matroskaenc.c
>> index 0878cb5..286b8b4 100644
>> --- a/libavformat/matroskaenc.c
>> +++ b/libavformat/matroskaenc.c
>> @@ -2264,17 +2264,19 @@ static int mkv_write_trailer(AVFormatContext *s)
>>         end_ebml_master_crc32(pb, &mkv->info_bc, mkv, mkv->info);
>> 
>>         // update stream durations
>> -        if (mkv->stream_durations) {
>> +        if (!mkv->is_live && mkv->stream_durations) {
>>             int i;
>> +            int64_t curr = avio_tell(mkv->tags_bc);
>>             for (i = 0; i < s->nb_streams; ++i) {
>>                 AVStream *st = s->streams[i];
>> -                double duration_sec = mkv->stream_durations[i] * av_q2d(st->time_base);
>> -                char duration_string[20] = "";
>> 
>> -                av_log(s, AV_LOG_DEBUG, "stream %d end duration = %" PRIu64 "\n", i,
>> -                       mkv->stream_durations[i]);
>> +                if (mkv->stream_duration_offsets[i] > 0) {
>> +                    double duration_sec = mkv->stream_durations[i] * av_q2d(st->time_base);
>> +                    char duration_string[20] = "";
>> +
>> +                    av_log(s, AV_LOG_DEBUG, "stream %d end duration = %" PRIu64 "\n", i,
>> +                           mkv->stream_durations[i]);
>> 
>> -                if (!mkv->is_live && mkv->stream_duration_offsets[i] > 0) {
>>                     avio_seek(mkv->tags_bc, mkv->stream_duration_offsets[i], SEEK_SET);
>> 
>>                     snprintf(duration_string, 20, "%02d:%02d:%012.9f",
>> @@ -2284,6 +2286,7 @@ static int mkv_write_trailer(AVFormatContext *s)
>>                     put_ebml_binary(mkv->tags_bc, MATROSKA_ID_TAGSTRING, duration_string, 20);
>>                 }
>>             }
>> +            avio_seek(mkv->tags_bc, curr, SEEK_SET);
>>         }
>>         if (mkv->tags.pos && !mkv->is_live) {
>>             avio_seek(pb, mkv->tags.pos, SEEK_SET);
> 
> 
> Ping. It's a recent regression on a muxer, so I'd like to solve it asap.
> I'll push it later today if nobody comments.

I tested this and it does fix the issue so that the added "key" tag is properly formed, whereas the tag is only null bytes without the patch. Thanks!
Dave Rice