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

[Stefano Sabatini]

On date Thursday 2010-12-23 01:37:00 +0100, Stefano Sabatini encoded:
> On date Sunday 2010-12-19 20:43:16 +0100, Stefano Sabatini encoded:
> > On date Saturday 2010-12-18 14:07:47 +0100, Michael Niedermayer encoded:
> [...]
> > > No, vflip flips the linesize.
> > > This fliped buffer is passed on by start_frame to the next filter and if that
> > > doesnt support it the existing code copies it
> > > The previous filter is not affected by start_frame messing with line sizes,
> > > It cant be affected because that would be a bug. A filter can have a static
> > > buffer that it passes on and it can alraedy have rendered into this buffer
> > > theres no way start_frame could tell the previous filter render fliped at that
> > > time. Only though get_video_buffer() can teh previous filter be brought to
> > > render upside down.
> > > 
> > > Thus if the previous filter uses get_video_buffer() it receives frames with
> > > negative linesize (if supported) and start_frame then also receives these
> > > buffers with negative linesize and it changes them to positive by fliping
> > > linesize and vissual image
> > > If OTOH the previous filter does not use get_video_buffer() or negative
> > > linesizes arent supported somewhere along the path then start_frame gets
> > > positive linesize frames and flips them to negative and (its the identical
> > > operation as previous) if now a downstream filter cant handle negative linesizes
> > > it gets copied before in that filters start_frame
> > 
> > OK, this explanation was useful, thanks.
> > 
> > Now I still can't find a way to avoid the copy in the filter, anyway
> > the new approach is indeed much simpler.
> > -- 
> > FFmpeg = Foolish and Fast Marvellous Pure Elastic God
> 
> > From ee6dc086923ed994a5dd70ab79513d9a510c29ce Mon Sep 17 00:00:00 2001
> > From: Stefano Sabatini <stefano.sabatini-lala at poste.it>
> > Date: Sun, 19 Dec 2010 16:35:50 +0100
> > Subject: [PATCH] Introduce the AV_PERM_NEG_LINESIZES flag, which allows to explicitely
> >  request a buffer which can have negative linesizes, so that if it is
> >  not specified in the permissions for the requested buffer the returned
> >  buffer must have positive linesizes.
> > 
> > This is required in particular with direct rendering as implemented in
> > ffplay, as some codec cannot process an image buffer with negative
> > linesizes.
> > 
> > Fix issue #1913.
> 
> Ping.

I'll apply in few days if I see no comments.
-- 
FFmpeg = Formidable and Fostering Mean Powerful Explosive Gadget