Archives June 2012

Alsa Loopback Devices for Fun, but not yet profit...

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 ...

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ALSA Loopback for Fun and Profit

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
    pcm "hw:Loopback{{spk}},0,0"
    rate 48000
    format S16_LE
pcm.monitor{{spk}}_snoop {
  type dsnoop
  ipc_key 68659{{spk}}
    pcm "hw:Loopback{{spk}},1,0" ...

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Really Dumb HTML5 Video Tag Back-end

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 ...

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How can an audio server take up 900MB of RAM?

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 ...

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Experience has some value... and risk

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 using distribute.  Run your unittests with Nose.  Use sphinx and embedded doctests.

You tell someone that ...

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