[FFmpeg-trac] #9001(ffmpeg:new): concat demuxed ASS subtitles don't work
FFmpeg
trac at avcodec.org
Thu Aug 5 07:45:46 EEST 2021
#9001: concat demuxed ASS subtitles don't work
-------------------------------------+-------------------------------------
Reporter: Gregory | Owner: (none)
Beauregard |
Type: defect | Status: new
Priority: normal | Component: ffmpeg
Version: git-master | Resolution:
Keywords: ass libass | Blocked By:
subtitles concat |
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
-------------------------------------+-------------------------------------
Description changed by Gregory Beauregard:
Old description:
> 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 `assconcatsamp1.mkv` and
> `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 `ffmpeg-20210804-124257.log`
>
> The output `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. It's failing at lines with dupe frame numbers. The G-li-co
> part has high frame numbers not encountered in the first file.
New description:
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 `assconcatsamp1.mkv` and
`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 `ffmpeg-20210804-124257.log`
The output `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.
--
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Ticket URL: <https://trac.ffmpeg.org/ticket/9001#comment:11>
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