[FFmpeg-trac] #3852(ffmpeg:new): Specifing subtitle timing in fast seek mode

[FFmpeg]

#3852: Specifing subtitle timing in fast seek mode
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             Reporter:  ghospich  |                     Type:  enhancement
               Status:  new       |                 Priority:  normal
            Component:  ffmpeg    |                  Version:  2.3
             Keywords:            |               Blocked By:
             Blocking:            |  Reproduced by developer:  0
Analyzed by developer:  0         |
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 == Motivation: ==
 When burning subtitles in fast seek mode, there is no way to specify
 subtitle timing. For example.

 {{{
 ffmpeg -ss 102.042 -t 24.250 -i sintel-1024-surround.mp4 -an -c:v libvpx
 -vf scale=640:-1,subtitles=sintel_en.srt out.webm
 }}}

 That way subs wouldn't be burned into video, because ffmpeg burns them
 with timing starting from 00:00:00 (there is no phrases in first minutes
 of video). For some reason in fast seek mode timing not passed to
 subtitles, and subtitles just simply start from the beginning.

 However, in regular slow seek mode everything is fine.
 {{{
 ffmpeg -i sintel-1024-surround.mp4 -ss 102.042 -t 24.250 -an -c:v libvpx
 -vf scale=640:-1,subtitles=sintel_en.srt out.webm
 }}}

 That way subtitles burned correct, and there is no need in explicitly
 specifying timing for subtitles.
 But slow seek mode is not convenient. There is often a very huge delay
 before encoding start that way, which is only get worse on huge files.

 == Enhancement proposal: ==
 I'm not sure why subtitles doesn't timing right in fast seek mode, so i
 did not opened this issue as 'bug'. If anything, i'll create another
 issue.

 So, maybe add option 'ss' to filter http://ffmpeg.org/ffmpeg-
 filters.html#subtitles-1 with same function as -ss in ffmpeg itself? This
 would be simple and convenient workaround.
 The ss option would specify from what point ffmpeg should start subtitles,
 explicitly.

 There is already such option in ffmpeg itself, so in 'subtitles' it
 wouldn't be a foreign.
 And with this option it would be finally possible to burn subtitles in
 fast seek mode.

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Ticket URL: <https://trac.ffmpeg.org/ticket/3852>
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