Hi Ken!
2012/10/29 Ken Restivo <[email protected]>:
> Hello folks, thanks for liquidsoap. I'm very glad someone created a streaming
> engine written in a functional language.
Thanks!
> Earlier this summer I set up a server for a micropower radio station in a
> remote location.
>
> It's running an old 3Ghz P4 with 2GB RAM, Ubuntu 10.04, and airtime.
>
> They wanted a jukebox for times there was no scheduled show playing, so,
> rather than tweak airtime, I set up a separate liquidsoap instance that ran a
> custom script. The script is below.
>
> It basically plays a jukebox, but falls forward to a live stream or to
> airtime, if either of those become available. It worked for a month or two
> flawlessly.
>
> The problem is, after a few months running, that it'd periodically stutter
> approximately 400ms of audio endlessly, then after 10-60 seconds move on to
> another frame, stutter that one, then it'd do a scrambled-sounding insane
> thing that sounds like an mp3 stream seeking past its key frame, then go back
> to stuttering, for hours. The problem would clear itself after some hours had
> passed. CPU usage was minimal at those times. There's no RT kernel, but I had
> liquidsiap nice'd -20 so it ran with higher priority than anything. The
> problem seems to happen randomly, intermittendly, typically once or twice a
> day, at no predictable time, and regardless of whether the active source is
> the jukebox, the livestream, or the airtime stream.
>
> The logs all look completely normal, no errors, no overruns, etc. At one
> point I did see an overrun, at the point where the error STOPPED happening,
> not when it started, which was odd. At the time that it's stuttering, the
> jukebox (or livestream, or airtime), looks like it's just cruising along
> doing what it's supposed to be doing.
>
> This was with Ubuntu's (old) liquidsoap package. I built a custom
> liquidsoap-1.0.1 from source, installed it, and ran that.... and it did not
> solve the problem.
>
> I've since ditched the separate liquidsoap instance completely, and now run
> these functions from inside airtime. It did not solve the problem.
>
> I asked on the linux audio list, and one of the ALSA devs pointed out that
> stuttering is caused by the application not sending data to the driver, so
> the hardware just keeps playing the same frame over and over again until it
> gets a new one from the application. But this isn't one frame (~40ms) it's a
> 400ms chunk. And the error indicates something more complex.
>
> Since this is airtime, I'm certain I'll get at least one reply telling me to
> go ask the Airtime people. They, in turn, sent me here. I did just today
> upgrade to airtime 2.2 which uses liquidsoap 1.0.1, but I didn't see any
> issues related to this problem, or anything in the changelog indicating it
> fixed it. Though, they are now using mp3replaygain in this new version, so
> CPU usage has gone sky high. I'll know by tomorrow if the upgrade fixed
> anything.
>
> My questions are:
>
> 1) Are there any things in the below script that look like the could cause
> liquidsoap to do this crazy thing? I am not new to functional programming or
> linux audio, but I am new to liquidsoap. Am I doing anything obviously wrong
> in the code below?
>
> 2) How would I find out when is happening, or that it had happened? I found
> the rms() command, which looks like it could be helpful for detecting
> silence. But what unit of sound is this 400ms chunk? What cuts it up into
> those size hunks? Is there some way to compare whether two or more sequential
> blocks like that are exactly equal to each other (and flag it perhaps as an
> error)?
>
> 3) How could I get more data as to what exactly is wrong?
Logs could help, particularly in verbose mode -- set("log.level",4)
As for your issue, I would suspect some bug with the alsa
driver/output. First thing to try to confirm that would be to use an
alternative output. I'd suggest output.ao which is generally the most
robust.
If output.ao works and you want to help us fixing the bug, even though
your jukebox should be now working, then we could try to see what
audio card you are using. However, debugging alsa on a card that we do
not own is kinda tricky.. You may also want to test with or without
the bufferize option.
Good luck,
Romain
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