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

Nicolas George george at nsup.org
Wed May 10 23:28:22 EEST 2017

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.


  Nicolas George
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