[FFmpeg-devel] manually hacked configure options increase h264 decoding speed significantly

Hendrik Leppkes h.leppkes at gmail.com
Thu Oct 20 11:29:06 CEST 2011


On Thu, Oct 20, 2011 at 10:41 AM, madshi <madshi at gmail.com> wrote:
> Here's the list of changes I'm currently doing manually to
> config.h:
> #define HAVE_CMOV 1
> #define HAVE_FAST_CLZ 0
> #define HAVE_FAST_CMOV 1
> #define HAVE_ISATTY 0
> #define HAVE_MEMALIGN 1

HAVE_CMOV and HAVE_FAST_CMOV are automatically set if you run
configure with the appropriate settings, for example "--arch=x86
Without the --cpu flag its compiled for 386 i think, which probably
didn't have CMOV yet.

HAVE_FAST_CLZ is auto-detected to 1 by configure, but doesn't seem to
influence the speed (much).

HAVE_ISATTY makes no real difference to the libraries, its only used
by the applications, so who knows why ffdshow sets it.
I can confirm however that HAVE_EBP_AVAILABLE does increase the
single-threaded performance of about 10%, not sure why the
auto-detection fails, though.

- Hendrik

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