Dec 25, 2010

Commandline pulseaudio mixer tool

Some time ago I decided to check out pulseaudio project, and after a few docs it was controlling all the sound flow in my system, since then I've never really looked back to pure alsa.
At first I just needed the sound-over-network feature, which I've extensively used a few years ago with esd, and pulse offered full transparency here, not just limited support. Hell, it even has simple-client netcat'able stream support, so there's no need to look for a client on alien OS'es.
Controllable and centralized resampling was the next nice feat, because some apps (notably, audacious and aqualung) seemed to waste quite a lot of resources on it in the past, either because of unreasonably-high quality or just suboptimal alghorithms, I've never really cared to check. Alsa should be capable to do that as well, but for some reason it failed me in this regard before.
One major annoyance though was the abscence of a simple tool to control volume levels.
pactl seem to be only good for muting the output, while the rest of pa-stuff on the net seem to be based on either gtk or qt, while I needed something to bind to a hotkeys and quickly run inside a readily-available terminal.
Maybe it's just an old habit of using alsamixer for this, but replacing it with heavy gnome/kde tools for such a simple task seem unreasonable, so I thought: since it's modern daemon with a lot of well-defined interfaces, why not write my own?
I considered writing a simple hack around pacmd/pacli, but they aren't much machine-oriented and regex-parsing is not fun, so I found that newer (git or v1.0-dev) pulse versions have a nice dbus interface to everything.
Only problem there is that it doesn't really work, crashing pulse on any attempt to get some list from properties. Had to track down the issue, good thing it's fairly trivial to fix (just a simple revert), and then just hacked-up simple non-interactive tool to adjust sink volume by some percentage, specified on command line.

It was good enough for hotkeys, but I still wanted some nice alsamixer-like bars and thought it might be a good place to implement control per-stream sound levels as well, which is really another nice feature, but only as long as there's a way to actually adjust these levels, which there wasn't.

A few hours of python and learning curses and there we go:

ALSA plug-in [aplay] (fraggod@sacrilege:1424)        [ #############---------- ]
MPlayer (fraggod@sacrilege:1298)                     [ ####################### ]
Simple client (TCP/IP client from 192.168.0.5:49162) [ #########-------------- ]

Result was quite responsive and solid, which I kinda didn't expect from any sort of interactive interface.

Guess I may be not the only person in the world looking for a cli mixer, so I'd probably put the project up somewhere, meanwhile the script is available here.
The only deps are python-2.7 with curses support and dbus-python, which should come out of the box on any decent desktop system these days, anyway. List of command-line parameters to control sink level is available via traditional "-h" or "--help" option, although interactive stream levels tuning doesn't need any of them.
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