[FFmpeg-cvslog] Support changing pixel formats on avfilter input.

[Stefano Sabatini]

On date Monday 2011-04-04 11:52:43 +0200, Michael Niedermayer wrote:
> On Mon, Apr 04, 2011 at 10:59:50AM +0200, Stefano Sabatini wrote:
> > On date Monday 2011-04-04 03:15:04 +0200, Michael Niedermayer wrote:
> > > On Sun, Apr 03, 2011 at 08:11:40PM +0200, Stefano Sabatini wrote:
> > > > On date Sunday 2011-04-03 18:20:09 +0200, Michael Niedermayer wrote:
> > > > > ffmpeg | branch: master | Michael Niedermayer <michaelni at gmx.at> | Wed Mar  9 15:13:59 2011 +0100| [7d948dc424c3620e351d27afdf933c99f9435467] | committer: Michael Niedermayer
> > > > > 
> > > > > Support changing pixel formats on avfilter input.
> > > > > Fix issue2217
> > > > > Signed-off-by: Michael Niedermayer <michaelni at gmx.at>
> > > > > 
> > > > > > http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=7d948dc424c3620e351d27afdf933c99f9435467
> > > > > ---
> > > > > 
> > > > >  ffmpeg.c                  |    5 ++-
> > > > >  libavfilter/vsrc_buffer.c |   53 +++++++++++++++++++++++++++++++++++++++++++-
> > > > >  libavfilter/vsrc_buffer.h |    4 +++
> > > > >  3 files changed, 58 insertions(+), 4 deletions(-)
> > > > 
> > > > Please revert this, this is not the proper way to fix it (and is
> > > > introducing several design problems).
> > > 
> > > elaborate please
> > > i know this isnt ideal but ideal is not going to happen anytime soon
> > > and this works the code before crashed
> > 
> > It is adding a dependency on libswscale to vsrc_buffer
> 
> Is libavfilter usefull without swscale?

It depends on what you mean by "useful". If you are on Mars, your life
depends on this tiny micro device with 200KB of RAM doing its
filtering work (and no need for fancy libswscale), yes libavfilter
with no scale is useful.

But the point here is different, vsrc_buffer is no special so if you
add a scale there then you should add the same in the other
sources. The proper solution is fixing the problem at the framework
level, rather than in each source.

> That is a video filter framework without the ability to convert between
> pixel formats and thus without the ability to connect some filters
> when they dont support a common format?
> 
> We can of course put the code under #if CONFIG_SWSCALE ...

> 
> 
> > 
> > It is extending a problematic API (and thus breaking my vsrc_buffer patches)
> 
> yes, that can be fixed though
> 
> 
> > 
> > It's not the proper way to fix it, this should be done by implementing
> > filterchain re-configuration rather than adding an hack in a random
> 
> 
> > source. I don't mind if you add the code to ffmpeg.c, but extending a
> > public interface this way is not acceptable IMO.
> 
> All applications need this code, ffplay for example needs it too and
> doesnt have it currently.
> So whichever way it is implemented, IMHO it should be in libavfilter
> and not duplicated in each application
> 
> Also filter chain reconfiguration alone
> does not solve the bug, applications still would need to inject a
> scale filter to ensure the output doesnt change.

This can be easily done by adding a fixed scale at the end of the
filterchain.
 
> I dont mind reverting this at all if you want, but i
> need a fix for this in 0.6.90 and if this hack is the best we have
> i will use it. If some better solution becomes available in time ill
> use the better solution in 0.6.90 of course

I'm having a look at how video resample works in ffmpeg.c. Also
rememeber that vsrc_buffer.h is going to be public API, and I would
like to avoid polluting it with random hacks (and then have users
complaining about broken API).