[FFmpeg-devel] [PATCH] make sure blending the subtitle does not write outside buffer

Reimar Döffinger Reimar.Doeffinger
Sun Aug 5 13:09:01 CEST 2007

On Sun, Aug 05, 2007 at 12:50:28PM +0200, Michael Niedermayer wrote:
> On Sun, Aug 05, 2007 at 12:36:34PM +0200, Reimar D?ffinger wrote:
> > On Sun, Aug 05, 2007 at 12:12:26PM +0200, Michael Niedermayer wrote:
> > > On Sun, Aug 05, 2007 at 11:00:04AM +0200, Reimar D?ffinger wrote:
> > > > attached patch fixes the subtitle rectangles so they do not lie outside
> > > > the video, which can cause crashes.
> > > 
> > > hmm, this seems like a hack to me
> > > shouldnt blend_subrect "skip" the parts of a rectange which are outside
> > > of the image?
> > 
> > well, unfortunately blend_subrect does not currently know the size of
> > the image. But more importantly, what is the point of showing half-cut
> > subtitles? At least I don't have any use for subtitles where I can read
> > e.g. only the upper half.
> A. the x/y/w/h of the subtitle is wrong
> -> fix the code so its not wrong

Well, this patch fixes it in ffplay :-P. The problem is, how should this
be fixed? In the subtitle decoder? Not only don't I think the decoder
should mess with it, it also misses two essential pieces of information:
1) The resolution of the video being played (easy to fix but maybe hackish)
2) The resolution for which the subtitles were created (impossible in
the general case).

> B. the x/y/w/h of the subtitle is correct
> -> you should display the subtitle at that position
> if the video for example is croped then i would argue that the x/y/w/h
> of the subtitle is wrong if its not moved to a more appropriate place
> but if on a non croped video some subtitle lets say moves off the screen
> slowly forcing that to stay on the screen is not correct

I disagree. Maybe the subtitle was created for a device that always has
a large border to the right or the bottom? Is it really a good idea to
not show that part of the subtitle at all, possibly making it entirely
useless or is it better to ignore the position information instead?

Reimar D?ffinger

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