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

[James Almer]

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);
-- 
2.9.1