[FFmpeg-devel] Slice direction in swscale.

[Michael Niedermayer]

On Wed, Sep 09, 2009 at 06:51:06PM -0300, Ramiro Polla wrote:
> On Tue, Sep 8, 2009 at 8:57 PM, Michael Niedermayer <michaelni at gmx.at> wrote:
> > On Tue, Sep 08, 2009 at 05:49:19PM -0300, Ramiro Polla wrote:
> >> On Mon, Sep 7, 2009 at 3:31 AM, Ramiro Polla<ramiro.polla at gmail.com> wrote:
> >> > 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,
> >> > 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?
> >>
> >> Alternatively we could document it with attached patch.
> >>
> >> Ramiro Polla
> >
> >> ?swscale.h | ? ?3 +++
> >> ?1 file changed, 3 insertions(+)
> >> cad71f58ca1ef8fb0a27b0885eb0e819b587b227 ?document_slices.diff
> >> Index: swscale.h
> >> ===================================================================
> >> --- swscale.h (revision 29662)
> >> +++ swscale.h (working copy)
> >> @@ -136,6 +136,9 @@
> >> ? * Scales the image slice in srcSlice and puts the resulting scaled
> >> ? * slice in the image in dst. A slice is a sequence of consecutive
> >> ? * rows in an image.
> >> + * Slices can be bottom to top or top to bottom.
> >
> > ok
> 
> Committed.
> 
> >> ?The direction will be
> >> + * detected in the first call and must be maintained throughout all
> >> + * subsequent uses.
> >> ? *
> >
> > i think this should be easy to fix, do we need more than reseting SliceDir?
> 
> How far do we want to support changing slice direction? In a per-frame
> basis, or in a per-slice basis? (as in we track continuity and check
> for the corner cases Y==0 or Y+H==height). Per slice would scale
> incorrectly because we would use old buffers.

per frame of course

[..]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

It is not what we do, but why we do it that matters.
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