[FFmpeg-devel] [PATCH] Change default behaviour of scale filter from 'progressive' to 'auto'

Michael Niedermayer michaelni at gmx.at
Tue May 1 12:38:04 CEST 2012

On Tue, May 01, 2012 at 11:12:33AM +0100, Tim Nicholson wrote:
> On 01/05/12 09:26, Michael Niedermayer wrote:
> > On Tue, May 01, 2012 at 08:29:47AM +0100, Tim Nicholson wrote:
> >> On 30/04/12 14:44, Michael Niedermayer wrote:
> >>> On Tue, Apr 17, 2012 at 10:15:15AM +0100, Tim Nicholson wrote:
> > [...]
> >>> I think the patch is correct but until the input interlace flag is
> >>> ALOT more reliable i dont think we should apply this as it likely
> >>> would worsen the overall results for the end user, 
> > [..]
> >>
> >> I therefore wonder if a better solution at this stage would be to add an
> >> additional SWScaler AVOption to enable selecting the default mode.
> >> Current users would see no change, and those who need it could simply
> >> add the option to their command line and get the results they need in a
> >> more elegant and simple manner than described previously.
> >>
> >> I will try and bone up on the SWScaler API and see what it would take to
> >> achieve that if you think that approach might work.
> > 
> > I think adding more possibly values to the interlace field used in
> > libavfilter is better. Its not certain the interlace state is the
> > same in the whole filter graph, also other filters may similarly
> > need to accurately know the interlacing/progressive state
> Is that not what the setfield filter does if used at the start of a
> filtergraph? I have already added in the ability to force progressive as
> well as the previous tff|bff options. However it doesn't seem to help
> the case of auto inserted "scale 0".

setfield can just set interlaced to 0 or 1
mpeg2 when marked as interlaced or dv when marked as interlaced
also set it to 1 so the scale filter cant distinguish them
if setfield could set it to 2 then scale in auto mode (with your patch)
could take 2 as interlaced and 0/1 as progressive
the user could then override it easily with setfield and the
unreliable flags from mpeg2 (and in case of the reg tests at least)
also dv wouldnt cause a problem

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