[FFmpeg-trac] #1924(avformat:closed): ASS subtitles are demuxed inconsistently
FFmpeg
trac at avcodec.org
Fri Nov 30 23:13:49 CET 2012
#1924: ASS subtitles are demuxed inconsistently
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Reporter: gjdfgh | Owner:
Type: enhancement | Status: closed
Priority: normal | Component: avformat
Version: unspecified | Resolution: invalid
Keywords: ass | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Comment (by gjdfgh):
This is not an issue with the ASS demuxer, but an issue with the ffmpeg
ASS packet format. It loses information. You can't distinguish multiple
identical events from each other. This happens always when getting ASS
subtitles from a ffmpeg demuxer.
It should happen when seeking back, so that the same subtitle events are
demuxed and displayed again. This assumes that mplayer doesn't remove all
events from to the ASS_Track on seeking.
Turns out it does.
Look at mplayer commit 31293, where this was explicitly "fixed", in
exchange for a worse user experience: you lose the nice behavior that
subtitles will display immediately if you seek back to somewhere you
already have watched, but it also compensates for ffmpeg's not so great
packet format.
So you can't demonstrate this issue with mplayer. In fact, ffmpeg pretty
much forces you to use ass_flush_events() on seeking to delete all
existing subtitle events, because otherwise subtitle events would
accumulate.
(Note: depending on how the file is muxed, subtitles can appear
immediately anywaqy when seeking back. Just increase the duration of the
subtitle events until it breaks.)
--
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/1924#comment:10>
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