Re: [9fans] audio standards -- too many to choose from

["Devon H. O'Dell" <devon.odell@gmail.com>]

2009/8/12 Tim Newsham <newsham@lava.net>:
>>>> - What software exists for each of these formats?
>>
>> If you are asking about non Plan9 software I'd start with
>> ffmpeg.
>>
>>>> - Which format is the most "popular"?
>>
>> I don't think I understand the question.
>
> Sorry, let me rephrase:
>  - Of the different audio driver interface designs
>    (audio(3), usb(4) and inferno usb(3)) which software
>    (p9 and limbo) uses each?
>  - Which of these interfaces is used the most?

I don't know which is used the most, but I don't think the Plan 9 ones
of them make particularly good sense to support multiple input formats
to multiple output formats. sox was mentioned here recently, and is a
great utility for doing the conversion. If we want a generic, reusable
audio layer, to *me* the Inferno one is best with:

audio
audioctl

It doesn't make sense to export files for volumes, codes, channels,
and other settings to me. This is because (at least with HDA cards)
you would end up with 5 bajillion files for controlling volume on each
individual channel. You'd end up with another file for reading/writing
codec settings. You'd end up with a file saying whether you preferred
digital output or analog output.

OSS relies heavily on ioctls for setting these things, but for good
reason. In our case, a standardized set of strings for the ctl file
seems best to me. If I want to change master volume, echo master
255.255 > /dev/audioctl. If I want to set digital out, echo output
channel digital > /dev/audioctl. etc. A more spread out filesystem
would make the ctl handler smaller, but would not reduce the amount of
code needed to support mixers / codecs / channels / whatnot (In fact,
you'd just have more code because you'd have to have functions for
reading/writing those files). Also, then you just need to come up with
strings -- you're just bit frobbing these things, and more complicated
filesystem hierarchy doesn't help explain it any better. echo 255 >
/dev/audio/mixer/channel/master/right; echo 255 >
/dev/audio/mixer/channel/master/left; just seems obtuse, and, as I
said, it's just adding more redundant code anyway.

To then play sound, you would probably have a sox-like converter
sitting on top of that (maybe even on top of /dev/audio?) that takes
input of a certain format and does either minimal conversion (i.e. a
card that supports XA ADPCM taking input from a playstation 2 sound
file not having any conversion at all, WAV going to the proper
byte-order PCM with the header stripped off, etc), or highest
resolution audio available (e.g. 5.1 flac getting converted to
whatever codec supports 5.1 audio).

Thoughts?

--dho