[MPlayer-dev-eng] [PATCH] A new ASS renderer

[Nicolas George]

Le primidi 1er vendémiaire, an CCXXI, Clément Bœsch a écrit :
> I'd unfortunately say that ASS performance is relevant when rendering
> complex karaoke or stuff like that, where the subtitles change all the
> time.

That is true, but this patch specifically does not help with that particular
case. In fact, it has been said that it made things slightly worse in this
case.

If I understand things correctly, there are two performance issues with the
way mplayer implements ASS blending: first, if several images overlap, the
blending on that area is done once per image. This is especially common with
ASS since each glyph has usually a body, an outline and a shadow, all
covering roughly the same area. Second, chrominance rendering is done by
first upscaling to the full resolution and then downscaling to the
chrominance subsampling.

The patch is too big for me to see at a first glance, but I suppose it
addresses the first problem, at the cost of doing the blending also in areas
that are not covered in glyphs. In other words, if "Hello World" is to be
rendered, the current code does it thrice for each of the 10 letters while
the proposed code would do it once for the whole sentence, including the
space. Depending on the layout and the exact implementation, it may or may
not be a global gain.

Regards,

-- 
  Nicolas George
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