[FFmpeg-devel] [PATCH] avutil/frame: document alignment and padding requirements

[Michael Niedermayer]

On Sun, Mar 17, 2013 at 03:30:05AM +0100, Clément Bœsch wrote:
> On Sun, Mar 17, 2013 at 03:23:19AM +0100, Michael Niedermayer wrote:
> > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > ---
> >  libavutil/frame.h |    8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/libavutil/frame.h b/libavutil/frame.h
> > index 8fc5814..2330840 100644
> > --- a/libavutil/frame.h
> > +++ b/libavutil/frame.h
> > @@ -78,6 +78,11 @@ typedef struct AVFrame {
> >      /**
> >       * pointer to the picture/channel planes.
> >       * This might be different from the first allocated byte
> > +     *
> > +     * Some decoders access areas outside 0,0 - width,height, please
> > +     * see avcodec_align_dimensions2(). Some filters can read upto 16 bytes
> 
> up to
> 
> Also, what are the filters? filters from libavfilter? Or this can refer to
> codec filters?
> 
> Isn't swscale outside libavfilter also doing such extra read?

yes, i had considered swscale a filter too.

swscale explicitly added


> 
> On a side note, a macro would be best.
> 
> > +     * beyond the planes, if these filters are to be used, then 16 extra
> > +     * bytes must be allocated.
> >       */
> >      uint8_t *data[AV_NUM_DATA_POINTERS];
> >  
> > @@ -87,6 +92,9 @@ typedef struct AVFrame {
> >       *
> >       * For audio, only linesize[0] may be set. For planar audio, each channel
> >       * plane must be the same size.
> > +     *
> > +     * For video the linesizes should be multiplies of the CPUs alignment
> > +     * preferrance. This is 16 or 32 for modern desktop CPUs
> 
> preference, missing trailing '.'

fixed


> 
> You said "should"; this isn't a requirement, right?

It depends on what you do with the AVFrames, some code can handle it
fine, some will print warnings, some will be slower, some will likely
crash.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

You can kill me, but you cannot change the truth.
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