[FFmpeg-devel] Question regarding DV decoder

Roman Shaposhnik rvs
Tue Nov 20 19:22:07 CET 2007

On Tue, 2007-11-20 at 09:52 +0100, Thorsten Jordan wrote:
> Dear ffmpeg developers,
> at the moment i am testing if it would be possible to get DV video
> decoding at realtime on a VIA Epia 1Ghz (C3-2, MMX, SSE, i686 compatible).
> The mainconcept decoder manages to decode with 28-34ms per 40ms frame,
> so it would be possible, where ffmpeg fails to do it below 40ms at average.

  Interesting data. I'm wondering where the real hot spot on that 
architecture is, though. 

> The dv video decoder code seems to be pure C (no mmx) with a FIXME that
> tells one should use dsputils rather. 

  Most of those FIXMEs are more or less artifacts by now. That is not
to say that speedup wouldn't be possible in other places. If my memory
serves me right dv_decode_ac() used to be the hottest place and it
doesn't lend itself easily to MMX-style of optimizations.

> Who maintains it, or may be so kind to give me a bit more information
> about it, e.g. like possibility of mmx support?

  I do maintain it (although not as actively as I used to). If you
have any practical question -- feel free to drop me an email.

> If my company decides to use it, i can myself try to add mmx support or
> other speedups, hopefully pushing it below 40ms.

  Patches are always welcomed. Although, personally I value
maintainability and correctness over raw speed.


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