[FFmpeg-devel] PAFF support h264 - preliminary patch as notes

[Michael Niedermayer]

Hi

On Tue, Jul 17, 2007 at 09:24:19AM +1000, Neil Brown wrote:
[...]
>  - Combine fields into frames.  I really don't know what the desired
>    result is here.  The decoding process will produce a series of
>    interlace fields, first a top field (lines 0,2,4,6,...) then a
>    bottom field (lines 1,3,5,7,...).  How should these be presented
>    to the application?
>    One option is to combine them into a single field.  However this
>    loses information as the fields should be separated by 1/50th of a
>    second (for the PAL case).
>    The other option would be to pass them back as individual fields
>    with half the expected number of lines and tell the application
>    that they are fields to be interlaced together.  However I have no
>    idea how to do that or if it is even possible.
> 
>    If the first option is best, then we need to hold on to the first
>    field until the second field is ready.  Then merge them together.
> 
>    If the second option is best (which I suspect to be the case), then
>    we need to decode fields densely (not leaving blank lines between
>    content lines, only using the top half of the buffer), which means
>    that my following patch is completely wrong as it gets the
>    decoding to use the full height, but only half the lines.
>    It would also mean that if we find a FRAME picture while expecting
>    interlacing, we need to split it into the two component frames to
>    return it to the application.  I think this would be a very
>    substantial code change.  It might make the code cleaner though.
> 
> I don't know if/when I might find time to work on this again so I am
> doing this brain dump now in case it might help someone else.  I would
> really like input on the question of how to return interlaced video
> fields before I even consider hacking on the code any more.

PAFF fields should be returned like MBAFF, that is 2 fields interleaved
into 1 frame

[...]
-- 
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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