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

[Stefano Sabatini]

On date Saturday 2010-12-11 14:49:54 +0100, Michael Niedermayer encoded:
> On Sat, Dec 11, 2010 at 02:12:10PM +0100, Stefano Sabatini wrote:
> > 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.
> 
> probably safest
> 
> 
> > 
> > > >  /**
> > > >   * 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.
> 
> vfw & dshow sources and sinks possibly will need it as windows stored (at least
> in the past) rgb bitmaps upside down
> raw rgb avi also has its negative linesize cases, and there are possibly
> other cases i dont remember now (binary codecs likely are amongth them too)
> 
> so i dont think vflip is the only relevant case
> 
> 
> > 
> > > 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.
> 
> in avfilter_start_frame()
> the linesize case can be added here:
>  /* prepare to copy the picture if it has insufficient permissions */
>     if ((dst->min_perms & picref->perms) != dst->min_perms ||
>          dst->rej_perms & picref->perms) {

how is this related? Also this will allow to save not more than 3
lines in the code (while making the core code more obscure).
 
> in vflips
> get_video_buffer()
> check if negative linesizes are permitted and if not return a buffer from
> default allocation or just skip the buffer flip

this is already implemented

The problem is how to integrate it with draw_slice()/end_frame(), and
support both the cases where the frame has to be inverted and not.

Patch updated with support for per-slice filtering.
-- 
FFmpeg = Funny & Fostering Miracolous Pitiless Extroverse Gadget