DNA Lounge: Source Code: Icecast Scripts

Icecast Scripts

by Jamie Zawinski

Here's how we do our streaming audio webcasts:

From 2001 to early 2006:
- There was a Linux machine inside DNA Lounge with an audio encoder card (a SoundBlaster Live.) This machine got an audio feed directly from the club's sound system.
- Scripts on that machine read raw audio from the card, converted it to MP3 in realtime, and sent a single 128k MP3 stream up a T1 to a server machine.
Since 2006:
- The machine inside DNA Lounge is a Macintosh Mini, running Nicecast. Same basic idea, but with much more reliable hardware and software.
The server machine is a CentOS PC with two 1.66GHz CPUs and 2GB RAM sitting in our ISP's colocation facility (so it has lots of outgoing bandwidth.)
That machine runs Icecast, which serves that 128k stream to the outside world.
However, we also used to offer the audio streams at lower bitrates, for people who have less bandwidth available to them. We don't do that any more, but the way that used to work is, there were some scripts running on the server machine that would:
- listen to the 128k stream;
- decode it;
- re-encode it at a lower bitrate;
- send that re-encoded stream back to the server for transmission.
Finally, you click on the link to the MP3 stream on our Audio Webcast page, which instructs your browser to launch your favorite MP3 player and connect to the stream on our server.

ice-downcoder.pl	This is the script that listens to one icecast stream, and then rebroadcasts it as another, after changing the bitrate. It uses LAME to decode and then re-encode the MP3 data. This is also the script that reads from the local sound card, converts it to an on-the-fly MP3 stream, and feeds that to an Icecast server.
shout-archive.pl	When the club is open we broadcast live audio; but when the club is closed, we used to re-broadcast audio from our archive of past live performances. We don't do that any more, but this is the script that did it. This script rolls through the directory of archived MP3 files and feeds them to the icecast server one after another, from oldest to newest. When it runs out, it wraps around and does it again.
ice-downcoders-initd	This is the /etc/rc.d/init.d/ script that launches a number of instances of ice-downcoder-loop.sh (one for each additional stream.)
ice-downcoder-loop.sh	This just runs ice-downcoder.pl in a loop, in case it exits. It is also somewhat smart about detecting network lossage: when the downcoder exits, it pings a particular host; if that host is not pingable, it waits until it becomes pingable before restarting the downcoder script.
write-metadata.pl	This is a handy little script for updating the metadata (streaming titles) in an existing Icecast stream.
update-downcoder-metadata.sh	This runs write-metadata.pl for each of the downcoded streams, so that all versions have the song titles in them.