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

[joy]

just finished real-mmap-support for alsa9-plugin. means sound will be
written directly into memory-mapped-audio-buffer. it currently
supports only signed-16-bit streams but it falls back to traditional
write-mode if another format is requested, its the default-mode
anyway.
i think this mmaped-write is a more cleaner architecture cause it
gives back the real value of written frames to mplayer where
normal-write only loop's as long as all frames are written, and returns
always len no matter if they are written or not.
i know that audio-processing doesn't cost so much cpu/io on modern
machines and i can't measure real differences between mmaped-mode and
traditional io-write but maybe it helps users on really slow hardware
who need all tweaks on cpu and io to get a vid running. i read also
somewhere that sound-quality should be better, could be theoretically
cause its one step shorter to the line-out, but assuming what is all
'humming' around in a normal pc it could never be like hifi-quality,
and it doesn't make any difference if sound-stream is written directly
into memory or not. i don't have a super hightech-hifi-setup so i
can't verify this anyway.
i would also reintroduce the obsolet -abs opt for alsa9 cause i think
it's usefull for some cases to have bigger/less buffer- and
fragmentsizes. for example if users run on slow hardware they can
increase buffer- and fragmentsize but on fast hardware they can lower
it, while gaining better latency. i prepared 4 most reasonable and
used modes for this:

  mode	   fragmentsize		buffersize
  -------------------------------------------
  1		512		8192
  2		1024		8192
  3		512		16384
  4		1024		16384 (consumer mode ;)

where mode 1 is default for mmap-write and mode 4 for 'normal'-write.
im thinking also of a mode 5 where the maximum buffersize is set
automatically but im not sure about this, cause 16384 frames
buffersize is more than enough for 99% of cases and its also the
dead-end for most soundcards supported by alsa i think.
any suggestions about this?
if it is accepted it would be cool if there would be some hint about
this in the documentation at least about the mmap-feature.


-- 
regards

____-
joy

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