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

Stefano Sabatini stefano.sabatini-lala
Sat Nov 6 18:21:55 CET 2010

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.
FFmpeg = Faithful Fanciful Mortal Purposeless Elected Goblin

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