[FFmpeg-devel] Why does vp56_init() sets avctx->width and avctx->height to 0?

[Stefano Sabatini]

On date Saturday 2008-08-30 16:55:57 +0200, Aurelien Jacobs encoded:
> Stefano Sabatini wrote:
> 
> > Hi,
> > 
> > this causes a bug both in ffprobe (prints widht=size=0) and causes
> > a division by 0 exception in libavfilter/vf_scale when it tryies
> > to set the parameters for the filter.
> > 
> > What's the point into setting those values to 0?
> 
> The point is that the actual frame width and height are not known
> at this point. They only get known after parsing the header of the
> first key frame.
> And also don't forget that those value may change at every key frame.
> The width/height is not an intrinsic property of a video stream, it's
> a property of each individual frame.

Thanks, it makes sense.

I wonder if this is a property of some some codecs, and if it would be
useful to mark somewhere this capability (for example
CODEC_CAP_VARIABLE_VIDEO_FRAME_SIZE).

And for what regards libavfilter: for what I understood, the
capabilities negotiation between the filters happens during the
initialization of the filters graph, is libavfilter supposed to manage
cases when the video frame size may change after the initialization?

Regards.
-- 
FFmpeg = Frightening & Funny Magical Portable Easy Gorilla