concat demuxed ASS subtitles don't work
|Reported by:||Gregory Beauregard||Owned by:|
|Version:||git-master||Keywords:||ass libass subtitles concat|
|Blocking:||Reproduced by developer:||no|
|Analyzed by developer:||no|
Description (last modified by )
ffmpeg version used: master as of 2021-08-04
Summary of the bug: The subtitles filter fails to display concat demuxed ASS/SSA subtitles due to choking on the frame number.
How to reproduce:
Attached are two sample videos
assconcatsamp2.mkv. We concat demux these files while rendering out the subtitles:
Create a new file
concatplaylist.txt in the same directory as the samples that contains the following (or download attached):
ffconcat version 1.0 file assconcatsamp1.mkv file assconcatsamp2.mkv
Now, we try to render out subtitles:
ffmpeg -report -f concat -safe 0 -i concatplaylist.txt -vf subtitles=concatplaylist.txt -c:v libx264 -b:v 1M -c:a libopus -b:a 96k -map 0:v -map 0:a -y assconcat.mkv
A log from running this is attached as
assconcat.mkv can be inspected to see all the subtitles in second clip weren't rendered except a part that says G-li-co.
When stored in MKV (ONLY when stored in MKV), ASS/SSA subtitle lines have an associated frame number that indicates their position within the original file. When concat demuxing two MKV files that each contain an ASS/SSA, the rendering will fail to render lines where it sees frame number dupes (i.e. in the second file that dupe from the first file). The G-li-co part rendered in the second file in the example has high frame numbers not encountered in the first file.
Change History (16)
comment:9 by , 11 months ago
|Summary:||concat demuxed ASS subtitles stop working with subtitles filter → concat demuxed ASS subtitles don't work|