[FFmpeg-devel] [RFC] How to fix DR+lavfi+vflip crash

[Stefano Sabatini]

On date Saturday 2010-11-06 18:21:55 +0100, Stefano Sabatini encoded:
> On date Saturday 2010-11-06 18:10:04 +0100, Stefano Sabatini encoded:
> > Hi,
> > 
> > as you may know the command:
> > ffplay INPUT -vf vflip
> > 
> > crashes with many video codecs. This is a regression introduced by the
> > direct rendering feature, since the codec request the frame to use for
> > putting the decoded frame, it gets a frame with negative linesizes and
> > crash
> > 
> > (BTW the smacker regression also seems to depend on diect
> > rendering, and precisely with the way the palette is initialized in
> > avfilter_default_get_buffer, which doesn't use ff_systematic_pal()).
> > 
> > A possible first step would be to define a CODEC_CAP_NEG_LINESIZES
> > capability (suggest a better name), and set it in all the codecs which
> > currently support this feature (I have no idea which of them, do
> > you?).
> > 
> > At this point I see two solutions. One solution would be to change
> > get_video_buffer(), and make it invert the buffer when it detects the
> > negative linesizes && the NEG_LINESIZES capability is not
> > supported, *or* auto-add another filter just before the ffplay source.
> > 
> > Such a filter (vflipfix - suggest better name) would work as a null
> > filter if the frame is not inverted, and would readjust the frame if
> > the linesizes are inverted.
> > 
> > The second solution seems simpler and cleaner.
> 
> To make it even more useful, we may add a capability to the filters,
> and auto-add the vflip-fix filter when building the filterchain, and
> fix all the filters which doesn't support negative linesizes.

Patchset attached.
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