[MPlayer-dev-eng] real mmap-support in ao_alsa

[Anders Johansson]

Hi,

I think this one is the most interesting one:
> SND_PCM_FORMAT_FLOAT_LE 
> Float 32 bit Little Endian, Range -1.0 to 1.0


> i can add it, its just a few lines of code but im not aware of one
> soundcard supported by alsa which does SND_PCM_FORMAT_FLOAT*. the
> 'best' cards i knew of do 24/32bit and even if they are capable of
> processing float they do it internally and 'truncate' it to 24bit
> again. 

Yes, I know, but some cards (sb audigy for example) do some processing
of the data in a custom chip on the board before before doing the
conversion.

> while im gathering information about this float/dsp thing i
> found that most audio-app-makers rely nowadays on simple
> cpu-horsepower cause you can do dsp-processing magnitudes faster with
> an athlon-1GHz cpu as with the best optimized assembler code for an 
> external dsp, but thats maybe not that what you want ;). 

Sometimes -- depends on what type of processing you are doing, and
what data rates you are dealing with. I would say that if you are
doing ordinary plain filtering then PCs is the way to go but if you are
developing adaptive algorithms then you can save quite a bit on
running in a DSP due to a more flexible architecture. Then of cause
there is the problem of buffer sizes in PCs and power consumption... But
yea, I am trying to get my boss to allow me to convert to Linux
instead of doing our stuff in DSPs.

> anyway, i add float-format and all the other possible formats and
> you can try to pass your filter generated data in
> SND_PCM_FORMAT_FLOAT. ao_alsa returns 1 on succes and 0 if it fails
> and the filter could probably fall back to an other format and try again.

I will propose a method for probing the ao drivers (real soon now
(tm)). I'll do the implementation for OSS. I'll be happy if you can do
the alsa driver, and I think there is someone that likes sdl and sun.

> btw. i found this nice article about converting c float to int cast
> without using inline assembler but still speeding it up a bit. maybe
> its usefull for you.
> 
> http://mega-nerd.com/FPcast/

Thanks It is.

> > > i actually started an ao_jack, 
> > 
> > Do you have any link to jack?
> > 
> 
> no, we just try to move our studio slightly to linux and we started
> using jack for connecting apps/effects. thats my only link ;).

No, I mean a URL link, or is jack a person?

//Anders