[FFmpeg-devel] Does i686 have MMX?

[Jason Garrett-Glaser]

> 2. ?By policy, make ffmpeg require MMX to run by default. ?Add a
> runtime check, just in case. ?Any --cpu that doesn't support MMX will
> error out unless the user specifies --disable-mmx too.
>
> Benefits: --cpu still makes logical sense, keeps the emms change, and
> we can enable CMOV by default too (i.e. if --cpu isn't set).
> Possible problems: this still breaks everyone's build scripts, but at
> least it'll break them loudly, so people will fix them.
>
> 3. ?By policy, make ffmpeg require MMX to run by default. ?Add a
> runtime check, just in case, telling the user to recompile without MMX
> if they're on an unsupported CPU. ?Don't check the user's --cpu option
> when it comes to validating this. ?This is what x264 does.
>
> Benefits: simple, doesn't break build scripts, and x264 showed that it worked.
> Possible problems: --cpu doesn't do quite what it implies -- adds
> runtime failure instead of compile-time.

Also, one extra benefit of either of these is that they let us add
inline MMX asm which is compiled by default.  This is useful in cases
like mid_pred, for example.

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