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

[Stefano Sabatini]

On date Thursday 2010-12-09 04:35:58 +0100, Michael Niedermayer encoded:
> On Mon, Dec 06, 2010 at 03:30:28PM +0100, Stefano Sabatini wrote:
> > On date Sunday 2010-12-05 12:12:58 +0100, Stefano Sabatini encoded:
> > > On date Friday 2010-12-03 00:03:15 +0100, Michael Niedermayer encoded:
> > > > On Sat, Nov 27, 2010 at 04:53:51PM +0100, Stefano Sabatini wrote:
> > > [...]
> > > > isnt it easier to handle (lack) of neg linesize support by using the premission
> > > > system?
> > > > like "i need a readable buffer" vs. "i need a buffer with positive linesize"
> > > 
> > > New attempt. Note the addition of a flag in start_frame(), I added a
> > > flag since it seemed more flexible.
> > 
> > Simpler.
> [...]
> > diff --git a/libavfilter/avfilter.h b/libavfilter/avfilter.h
> > index 5d34bee..194a614 100644
> > --- a/libavfilter/avfilter.h
> > +++ b/libavfilter/avfilter.h
> > @@ -86,6 +86,7 @@ typedef struct AVFilterBuffer {
> >  #define AV_PERM_PRESERVE 0x04   ///< nobody else can overwrite the buffer
> >  #define AV_PERM_REUSE    0x08   ///< can output the buffer multiple times, with the same contents each time
> >  #define AV_PERM_REUSE2   0x10   ///< can output the buffer multiple times, modified each time
> > +#define AV_PERM_POS_LINESIZES  0x20  ///< the buffer requested cannot have negative linesizes
> 
> i think POS is a bad term because it hints to position primarely before positive
> or anything else

I propose AV_PERM_POSITIVE_LINESIZES or AV_PERM_NONNEG_LINESIZES (the
latter is consistent with CODEC_CAP_NEG_LINESIZES), or we could invert
the logic and request AV_PERM_NEG_LINESIZES.

> >  /**
> >   * Audio specific properties in a reference to an AVFilterBuffer. Since
> > diff --git a/libavfilter/vf_vflip.c b/libavfilter/vf_vflip.c
> > index 95d90d3..84c92bd 100644
> > --- a/libavfilter/vf_vflip.c
> > +++ b/libavfilter/vf_vflip.c
> 
> a solution in vflip is not ideal as this would require each filter that
> could produce negative linesizes to duplicate that solution.

yes we currently have one filter with that feature and is called
vflip, I don't think we're going to have so many filters of that kind.

> a fix should be in the filter core, there already is code to copy a frame
> when permissions are not compatible and using that should be simpler than your
> patch

I thought about this and after some attempts I don't think it is worth
to follow this path, as it is complicating the core for a marginal
feature.

If you can show a detailed solution which is simpler than this then I
can try to implement it, otherwise I'll stick with this one.
-- 
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