[FFmpeg-devel] Slice direction in swscale.

Michael Niedermayer michaelni
Wed Sep 9 01:56:31 CEST 2009

On Mon, Sep 07, 2009 at 03:31:24AM -0300, Ramiro Polla wrote:
> Hi,
> In sws_scale() there is some code to adjust src and srcStride if it
> seems the slices go from bottom to top. This is traced back to r15249,
> and the discussion leading to the patch is here:
> http://thread.gmane.org/gmane.comp.video.mplayer.devel/25600/focus=25615
> I have also stumbled upon this:
> http://thread.gmane.org/gmane.comp.video.ffmpeg.devel/42415
> I have not been able to test this code, not even with the sample
> pointed at the first link above. The sample plays something very
> distorted in ffplay, something with a badly scaled chroma in mplayer,

even with a revission from that time?
if it does work, its of course interresting when it broke ...

> and plays properly in vlc.
> Does anyone know of a sample that triggers code? Certainly it's not
> with ffmpeg/ffplay, since we run sws_scale on the whole picture
> instead of slice-based, but I suppose this could be tested with
> mplayer.

> Anyways the sliceDir check is very hackish and undocumented. 


> Would it
> be acceptable for this to be removed and always require top-to-bottom
> strides or expect the user to flip things himself?

well, this appears inconvenient for the user as it means duplicated code

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Asymptotically faster algorithms should always be preferred if you have
asymptotical amounts of data
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