Opened 2 months ago

Last modified 5 weeks ago

#9843 new defect

Matroska muxer never returns avio markers

Reported by: Sesse Owned by:
Priority: normal Component: avformat
Version: git-master Keywords: mkv
Cc: Blocked By:
Blocking: Reproduced by developer: no
Analyzed by developer: no


The Matroska/WebM muxer has this code to send avio markers on sync points:

if (!mkv->cluster_pos)


av_rescale_q(pkt->dts, s->streams[pkt->stream_index]->time_base, AV_TIME_BASE_Q),
keyframe && (mkv->have_video ? codec_type == AVMEDIA_TYPE_VIDEO : 1) ? AVIO_DATA_MARKER_SYNC_POINT : AVIO_DATA_MARKER_BOUNDARY_POINT);

This was merged into FFmpeg in

commit dc62016c4b77a48284b24ad927eb68035b133925
Merge: a86fe0d738 71852a1ba8
Author: Matthieu Bouron <>
Date: Thu Jun 23 17:57:34 2016 +0200

Merge commit '71852a1ba89abc8749e309d9d662c49d47e19531'

Merged-by: Matthieu Bouron <>

However, it didn't take into account that this patch was already in the tree:

commit bda5b6627a558cf10c4d09eeff264289a1370cc1
Author: Aaron Colwell <>
Date: Wed Mar 14 21:40:29 2012 +0100

matroskaenc: change cluster_pos to use -1 as the "I'm not currently working on a cluster" signal instead of 0.

This avoids problems
where avio_tell() returns 0. I've updated all the checks against

Signed-off-by: Michael Niedermayer <>

So now mkv->cluster_pos cannot be 0, and the markers are never sent. It seems this functionality has been broken in FFmpeg since it was merged.

Changing the test to (mkv->cluster_pos == -1) instead seems to fix the issue, but someone should verify that this was indeed the intention.

Change History (1)

comment:1 by Carl Eugen Hoyos, 5 weeks ago

Keywords: mkv added
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