[linux-audio-dev] Oss & threading -- is it possible

[David Olofson]

On Friday 10 October 2003 17.41, hexe_2003 at directbox.com wrote:
[...]
> But well, If I synthize ( ? spelling) two signals and want to send
> them at  the same time to the device, my first idea'd be:
> 1.) Open /dev/dsp, maybe O_NONBLOCK | O_WRONLY
> 2.) thread
> 3.) two threads calculate the both signals
> 4.) sync them
> 5.) two threads write their signals to /dev/dsp
> 6.) threads close
>
> certainly some of this. I mean mp3blaster, for example, have
> several pids while playing audio streams, and it is basicly
> OSS-programming and not alsa.
> Am I so wrong ? ;)

Yep! ;-)

Synths, trackers, games and other "polyphonic things" at some point 
mix everything into a single stream that is sent to the audio device.

In general, all audio processing is done in a single thread, but in 
some cases, it can be pretty hard to get the processing deterministic 
enough that it can run in the audio thread without causing drop-outs. 
This is especially troublesome if you need low latency, as in games 
and other interactive applications.

This is probably why mp3blaster is using multiple threads; one for 
each mp3 stream (decoding into raw audio data) and one for mixing and 
output. There is most probably substantial buffering between the 
decoding threads and the mixer thread, as this would allow solid 
playback with less buffering (ie less laggy mixing controls) between 
the mixer and the audio device.


//David Olofson - Programmer, Composer, Open Source Advocate

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