[MPlayer-dev-eng] [PATCH 2/2] av_sub: support multiple rectangles.

[Reimar Döffinger]

On Mon, Apr 23, 2012 at 11:46:12AM +0200, Nicolas George wrote:
> Le quintidi 5 floréal, an CCXX, Reimar Döffinger a écrit :
> > I slightly disagree. Neither the OpenGL nor libswscale scalers are good
> > enough for subtitle scaling.
> 
> I trust you for OpenGL. But for libswscale, what problem do you see?

I remember it looking really bad in comparison, harder to read, blurry,
....

> I tried a random vobsub on top of a red background, first using mplayer's
> SPU scaler (scale=$size,expand=osd=1) and then using libswscale
> (expand=osd=1,scale=$size) to downscale to 320×180.

Of course I didn't downscale, I watch DVDs on a TV or computer monitor,
not my fingernail. I can easily believe that the spu scalers may suck
for downscaling, though I can't see downscaling as a relevant use-case
(even if I downscaled the video, for lots of DVDs I'd rather not
downscale the subtitles, they are rather small to begin with).
However you can see the issues even here: The black border is in some
areas on the top almost completely gone, spu scaler preserves them
better. So at least a colored, black and white background should be
tested, otherwise some issues can be missed.

> The result I found is that swscale default scaler (bicubic) looks better
> than spuaa 2 (which is, as the doc says, the best looking).

It is probably a bit a matter of taste, but for upscaling I believe it
is.
For downscaling 4 might be better, except that it looks to me like
it results in too high transparency...