[FFmpeg-trac] #9001(undetermined:new): concat demuxed ASS subtitles stop working with subtitles filter
FFmpeg
trac at avcodec.org
Sun Nov 22 20:11:36 EET 2020
#9001: concat demuxed ASS subtitles stop working with subtitles filter
-------------------------------------+-------------------------------------
Reporter: aphysically | Type: defect
Status: new | Priority: normal
Component: | Version: git-
undetermined | master
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Summary of the bug: The subtitles filter fails to reliably display concat
demuxed ASS subtitles
How to reproduce:
Download test files (3.6 MB): [https://gably.net/testcase/test1.mkv]
[https://gably.net/testcase/test2.mkv]
Each test file has 20 seconds of video with ASS subtitles. Note in
particular the last section of subtitles in the second clip. Concat demux
the subtitles and videos as follows. Once by converting first to text, and
once by leaving as ASS subtitles.
{{{
#!/bin/bash
rm -f playlist.txt
echo "file '$(readlink -f "test1.mkv")'" >> playlist.txt
echo "file '$(readlink -f "test2.mkv")'" >> playlist.txt
ffmpeg -f concat -safe 0 -i playlist.txt -ss 00:00:00 -c:s copy -map 0:s:0
-map 0:t? -y subs.mkv
ffmpeg -f concat -safe 0 -i playlist.txt -ss 00:00:00 -c:s text -map 0:s:0
-y textsubs.mkv
ffmpeg -f concat -safe 0 -ss 00:00:00 -i playlist.txt -vf
subtitles=subs.mkv -c:v libx264 -b:v 1M -c:a libopus -b:a 96k -map 0:v
-map 0:a -y concat.mkv
ffmpeg -f concat -safe 0 -ss 00:00:00 -i playlist.txt -vf
subtitles=textsubs.mkv -c:v libx264 -b:v 1M -c:a libopus -b:a 96k -map 0:v
-map 0:a -y textconcat.mkv
}}}
Observe that `concat.mkv` is missing some of the ASS subtitles at the end
of the second clip that `textconcat.mkv` is not missing. The subs are
present in `test2.mkv`. This bug was originally observed when
concatenating entire files as the ASS subtitles suddenly failing to render
entirely. Various insertions of `-fix_sub_duration` don't change the
situation. Note not including the `-ss` arguments produce other odd timing
problems, but this may need to be filed as a separate bug.
ffmpeg version: master
built on 2020-11-22 5 pm UTC
--
Ticket URL: <https://trac.ffmpeg.org/ticket/9001>
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