[FFmpeg-devel] [PATCH] PAFF: Derivation process for chroma motion vector

Michael Niedermayer michaelni
Mon Oct 15 20:39:32 CEST 2007

On Mon, Oct 15, 2007 at 12:51:45PM -0400, Jeff Downs wrote:
> On Mon, 15 Oct 2007, Loren Merritt wrote:
> > In MBAFF, the reference list is generated as a list of frames, and then 
> > split to make fields. So a field pair is always adjacent in the list, and 
> > ref_index&1 is the parity.
> > 
> > In PAFF, fields may be independently reordered in the list (and even if 
> > no reordering is used, the default order isn't always the same as 
> > MBAFF), so use pic->reference&1 instead. But you also need to change
> > pic_as_field() to set reference appropriately.
> > 
> > pic->reference&1 could work in MBAFF too, if you set reference
> > approriately in fill_mbaff_ref_list().
> Loren is right on in his description of the problem.
> I glossed over this when I originally wrote the PAFF support.
> The attached patch implements the above approach, fixing chroma MV offsets 
> for PAFF whilst not keeping around a second approach for MBAFF.
> I ran both current svn and svn+patch against all MBAFF complaince bit 
> streams from JVT.  Output of ffmpeg is equal w/ and w/out patch.
> Benchmarks results of 10 runs each (this was on PAFF content),
> Current svn:
> User: avg: 22.294  stddev: 0.027  med: 22.306
> svn + patch:
> User: avg: 22.194  stddev: 0.049  med: 22.177
> Suggested commit message:
> "Fix chroma mv offsets for PAFF in a way that is compatible with MBAFF by 
> setting Picture.reference to indicate parity for all Pictures in reference 
> list"

patch looks ok

btw, if you want a svn write account (and accept our development policy),
email diego a username+password (preferably gpg encrypted)

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Those who are too smart to engage in politics are punished by being
governed by those who are dumber. -- Plato 
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