Play With It Out Loud

I’m working on earning my “Subversive Radio Host” merit badge with my RaspberryPi. Once I’ve got the whole system worked out I’ll likely be doing a Hacker Public Radio episode about it. In the meantime, though, for testing purposes I have a feed from the local NOAA Weather Radio which I am feeding as 10kbps opus audio to an instance of icecast2.

I figured I’d post this since there’s a piece of information I found today regarding having a continuous stream, and someone else may find it useful.

I was finding that my stream to the icecast server, using the command line suggested by the opusenc man page, was spontaneously dying at almost precisely 6 hours, 12 minutes, and 50 seconds. For reference, here’s what the man page says (or at least has for quite some time now and did when I last checked it today) as a suggestion for live-streaming recorded audio in realtime:

arecord -c 2 -r 48000 -twav - | opusenc --bitrate 96 - - | oggfwd icecast.somewhere.org 8000 password /stream.opus

I was using the same string of commands, with minor changes (only one channel, –bitrate 12 [or 10], different address and credentials for oggfwd).

To cut the drama short, the problem turns out to be arecord. I still am not sure whether arecord was hitting a “maximum number of bytes” or “maximum run time” problem, but either way, it turns out you can just use sox (symlinked as “rec”) in its place, which is nice because I had been thinking about playing with having sox apply some filtering to remove noise, etc.

Here’s a suggested replacement command line for this purpose:
rec -c 1 -t wav - | opusenc --bitrate 10 - - | oggfwd icecast.somewhere.org 8000 password /stream.opus
(with the parameters adjusted to your own needs, of course).

It’s been going for over 7 hours now, so I’m assuming my problem is resolved. In the long run it won’t matter so much – my intended use-case in the end involves playing pre-recorded files (and would work perfectly with ices2‘s features if ices2 supported opus…), but for times when I may want to live-stream something, this may come in handy. With opus at 10-12kbps being still decent quality for voice, one ought to be able to feasibly live-stream audio even over a really slow pre-“3G” cellphone data link or dial-up modem in realtime.

Oh, speaking of “Subversive Radio Host” – using the clever pifm software turns the Raspberry Pi into a remarkably powerful transmitter. I think I’ve got my antenna trimmed down enough to make it a legal unlicensed transmitter (my original test was with a 20″ or so piece of alligator-clip wire that happened to be handy, and got the signal out to about three blocks away. Definitely too much power for legal unlicensed use.) I suspect with an ideal-length wire as an antenna you could cover a whole town, if you placed it well, and if you didn’t mind getting the FCC (or whoever your local regulatory agency is) very annoyed with you.

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