Well, the requirements that raised this thread should be fairly clear. For example,
ALTERNATIVE 1
snd_pcm_set_volume(snd_pcm_t* pcm, int volume)
and
snd_pcm_set_pan(snd_pcm_t* pcm, int pan)
using whatever value range makes the most sense, and perhaps some query on whether these controls are available from the pcm info. It's acceptable to have to explicitly ask for these controls using hw_params. The plug plugin could insert the route/volume plugin if these controls are asked for.
ALTERNATIVE 2
snd_pcm_set_volume(snd_pcm_t* pcm, int vol_left, int vol_right)
but I don't expect this to be useful, since there are probably some oddball devices out there that aren't able to control left and right volume independently like this.
ALTERNATIVE 3
Let each PCM channel have its own mixer control, like the EMU10K1 currently do. That is, use snd_pcm_info_get_subdevice() to get the index, then look up a volume control with a well-known name and the given index using the snd_ctl API to control the volume of that PCM stream. The name and semantics of that mixer control would have to be standardized and be the same on all devices that are capable of this feature.
What about 7.1 surround sound channels. All your suggestions only assume 2 PCM channels.
Although it might seem nice to add this to alsa, it is not exactly a difficult task for the application to do itself.
I suggested exactly what you suggested some time ago (see alsa-devel archives), but recently I have realised that there is little or no point.
The application will contain a user interface control for the volume, so one might as well adjust the volume in software as well. It is not even very CPU intensive.
Cheers James
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