[FFmpeg-devel] [PATCH 2/3] lavc: add a framework to fix alignment problems.

Michael Niedermayer michael at niedermayer.cc
Thu May 11 00:02:48 EEST 2017

On Wed, May 10, 2017 at 10:28:22PM +0200, Nicolas George wrote:
> Le primidi 21 floréal, an CCXXV, Michael Niedermayer a écrit :
> > fixed, and now your patchset seems to cause a 1% slowdown of the
> > example above
> Thanks. The slowdown is to be expected, since this filter used
> non-aligned frames which are now realigned. I guess you can get back the
> previous speed by setting "avctx->alignment = 0" in snow_encoder.init().

> The default in this patchset is 5 to fix all the alignment problems, at
> the cost of some slowdown in corner cases such as this one. I am not
> qualified to decide the best way of setting an optimal value to get
> speed without crashes. My opinion would be:
> - have avctx->alignment default to 0;
> - have all codecs with explicit assembly set avctx->alignment to the
>   required value;
> - have all codecs that use generic DSP code init it through a function
>   that sets the alignment accordingly.

run fate with intentionally misaligned frames, and make a list of
all codecs that dont crash and work fine.
These should not use realignment as they dont need it and would be
slowed down.


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

I know you won't believe me, but the highest form of Human Excellence is
to question oneself and others. -- Socrates
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