[FFmpeg-devel] libavfilter and subtitles (was: [RFC] Talk about subtitles)

Nicolas George nicolas.george at normalesup.org
Thu Dec 22 16:42:18 CET 2011

Le duodi 2 nivôse, an CCXX, Reimar Döffinger a écrit :
>> 	movie=input.vob [v]; smovie=input.mkv [s]; [v] [s] hardsub
>> then smovie has only the sparse output, it can not keep it in sync with the
>> video stream.
> What would be the point of that? If the inputs are different you can
> just read up to the next subtitle

That is a typo in my message: I meant to have the same file for both.

>				     for most formats that should not be
> that slow.

It also depends on the medium the file is read from: if it comes from a DVD
or a sshfs on a poor wifi, this is a problem.

> That breaks down as soon as you _want_ to have a significant delay
> between e.g. video and subtitle.

I am not sure I understand what you mean, but this need seems uncommon
enough to accept it to be somewhat less efficient and more verbose.

I mean, if you want video and subtitles from video.vob, in sync with one
another, you just write:

	movie=video.vob [v] [ax] [s] ; [v.0] [s.0] hardsub

and if for once you need them separately:

	movie=video.vob [v] [ax] [sx] ; movie=video.vob [vx] [ay] [s] ;
	[s.0] setpts=... [s2] ; [v.0] [s2] hardsub

With the current state of affairs, that would be written:

	movie=video.vob [v] ; smovie=video.vob [s] ;
	[s] setpts=... [s2] ; [v] [s2] hardsub

(or without the setpts part) I think the uncommon case is only slightly
worse while the common case is a huge improvement.


  Nicolas George
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