gst-plugins-base: videoconvert: prevent bad interlaced conversions

[David Schleef]

On Sat, Mar 23, 2013 at 02:14:38PM +0100, Sebastian Dröge wrote:
> > videoconvert: prevent bad interlaced conversions
> > 
> > Don't allow conversion that changes vertical subsampling if video
> > is interlaced.
> 
> This breaks backwards compatibility though... as previously videoconvert
> could convert between any color formats in any case.

I'm happy to revisit this if it actually causes regressions in
applictions.  But this falls in the class of "should never have
been allowed in the first place" bugs.

> What's wrong with changing the subsampling of interlaced video by
> changing it for each field separately (and e.g. not taking the average
> value of components from different fields) and then interleaving the
> fields again?

That would be much better than what happened before this patch.
However, it's not correct if you're planning to deinterlace or ivtc
the video.

The particular problem this fixes is decoding 10-bit 4:2:2, converting
to a format that yadif or ivtc understands, then converting to I420
for encoding.  videoconvert was converting to I420 at the first stage,
which is very much wrong.



David