[MPlayer-dev-eng] Some libass bugs

[Evgeniy Stepanov]

On Wednesday 23 May 2007, Vladimir Mosgalin wrote:
> Hi Compn!
>
>  On 2007.05.23 at 12:34:50 -0400, Compn wrote next:
> > >Also subtitle positioning keys (r and t) are not functional when -ass
> > >is in use.
> >
> > not sure if they are supposed to work with libass...
>
> Well why not? At least with ass = 1 in config, when libass is used to
> rendering plain srt subtitles which have no position information anyway.
> Right now this feature is lost.
>
> Actually, I think it might be implemented even for subtitles which
> specify position. For them, "subtitle position" value should work as
> vertical screen size in percents, i.e. when it's set to 90 and your
> screen's height is 1200 subtitles are rendered as if screen height is
> 1080, from the top of the screen, but not to the very bottom.

Positioned subtitles are often used to translate some sign or inscription and 
should not be moved. Everything else could be moved by changing MarginV.

> > also sub_step works for stepping back, but not forward.
> > sub_delay does weird things too :)
>
> sub_step works either way, but in mkv subtitles which are in the future
> haven't been extracted yet, so you obviously can't go forward - libass
> simply doesn't know about these subtitles. With external subtitle file
> or after you've seeked backwards you should be able to go forward.

This is also true for sub_delay. With a large positive sub_delay subtitles 
that should be displayed at some point of time could not be demuxed yet.

> However, sub_step has some very obscure bug, some subtitles can "fall
> out" and completely ignore sub_step command, i.e. when you do sub_step
> -1 you go two subtitles back, and when you do sub_step +1 after that you
> go two subtitles forward, and subtitle in the middle only renders
> regular way, there is no way to recall it with sub_step.

Do you have a sample ?