[MPlayer-dev-eng] [BUG] surround audio plugin broken

[Anders Johansson]

> Hi,
> 
> > > maybe we should change all codecs to output in their native formats only,
> > > and left all kind of downsampling, float2int etc to libaf.
> > > this way we lose conversions helped by the codecs (examples: liba52's
> > > float2int, channels downsampling, mp3lib's half or quarter freq decoding,
> > > mono decoding of stereo sterams, stereo decoding of mono streams).
> > 
> > This seems like something of a negative to me, especially with ac3
> > decoding...but I'm not sure how it works now. If there are only 2
> > output channels but the stream is 5.1 ac3, does liba52 really decode
> > all the channels and then downmix them, or can it just skip the
> > surround stuff and decode only l/r for better performance? If it can't
> > do that, it seems like a really desirable feature, especially since
> > ac3 decoding is so damn slow to begin with.
> 
> liba52 is very clever...
> it downmixes channels in freq space (with coeffs) and the imdct only
> the requested number of channels.

That means that if the highest frequency bins were set to 0 then
downsampling could be run without filtering... It would probably be
best to integrate that into liba52 however.

> also it can add a given bias value to the pcm values (while doint the imdct)
> helping the float2int process (there are integeronly tricks to convert an
> ieee float in a given range to integer) 

Do you know which file?
 
> A'rpi / Astral & ESP-team

//Anders