Archives June 2012

So you want to be able to capture the output of N Alsa "devices" (think N separate programs). It seems like the correct solution to this should be an Alsa loopback device... so, here's how to create them.

• Add snd-aloop to your /etc/modules
• Add a file named /etc/modprobe.d/alsa-aloop.conf (content below)
• Create a .asoundrc that makes ...

So I finally got the ALSA loopback working with gstreamer. Key is to use ALSA's plugs to get the right format on both sides of the capture:

{% for spk in cards %}
pcm.spk{{spk}} {
  type plug
  slave{
    pcm "hw:Loopback{{spk}},0,0"
    rate 48000
    format S16_LE
  }
}
pcm.monitor{{spk}}_snoop {
  type dsnoop
  ipc_key 68659{{spk}}
  slave{
    pcm "hw:Loopback{{spk}},1,0" ...

So you want to create a stupid-and-dirty HTML5 video tag to allow you to monitor a (local-only) multicast stream from your (Django + Nginx) web site?  Not something to be seen by "real people", but a way for you to see if anything is broadcasting?

This is a pretty simplistic thing, again; do *not* do ...

So we want to capture the (alsa) output of processes and pipe it into an mpeg-ts stream.  Except gstreamer's alsasrc can't do "monitor", so we wind up having to do a pulsesrc... which brings the server to its knees in a few minutes with memory exhaustion for no reason I can fathom.

Annoying part is ...

Each time I sit down to help someone relatively new to coding I find myself somewhat awe-struck at how much I've "forgotten".  Just install nginx with gunicorn and django in a virtualenv.  Package up your code with a setup.py using distribute.  Run your unittests with Nose.  Use sphinx and embedded doctests.

You tell someone that ...