[FFmpeg-soc] Status of the Dirac codec

Michael Niedermayer michaelni at gmx.at
Wed Sep 5 14:01:40 CEST 2007


On Tue, Sep 04, 2007 at 05:33:41PM +0200, Marco Gerards wrote:
> - Interleaving.  I just have to learn more about interleaving, if
>   FFmpeg supports this well, it should not be too hard I hope?

did you mean interlacing?

> - Global Motion Estimation is not supported yet.  The reference
>   implementations do not support it either, that is the main reason it
>   is still missing, it is impossible to test.

GME (on the encoder side) is _likely_ not very important, i wouldnt expect
much gains from it. in mpeg4 allmost all of the (small) quality/bitrate gain
GMC has is not due to global motion compensation itself but rather due to
a change to the used motion vector for skiped blocks

> Possible optimizations:
> - Write arithmetic (de)coding in assembler or so.  The people from BBC
>   research thinks arithmetic (de)coding causes the most significant
>   slowdown.  So focussing on this might speed up both the decoder and
>   encoder.  By not using GetBitContext/PutBitContext this can also be
>   speed up, but I am not sure how... I will have to use bit operations
>   anyways I think?

just curious, how much time is spend in arithmetic decoding in your codec?
arithmetic decoding shouldnt eat 90% of the time ...


> I am not sure how long we should wait
> to put this into SVN.  Perhaps we should wait until the Dirac codec is
> released?  Having Dirac support now is useless anyways I think.  In
> the meanwhile I can keep working at this without disturbing anyone in
> any way.  

personally i would prefer it to be moved to ffmpeg svn rather sooner than
later it would get more testing thus bugs will be found quicker and it would
also be more likely that other developers would contribute though i dont
think many will but who knows ...

> I wonder if I keep working in the same way I am used to when
> Dirac makes it into SVN or should I go through the devel list with
> patches or so?

no, just commit directly, patches would only be apropriate for code
outside dirac* or change for which you would like some comments
like maybe if you are unsure about some lavc API or whatever

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

In a rich man's house there is no place to spit but his face.
-- Diogenes of Sinope
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