[Icecast] About latency, PCM and clients compliance

Sylvain Le Beux sylvain at dailytlj.com
Thu May 30 16:34:38 PDT 2013


Hi all,

I am recently using icecast from server streaming, and even though I
succeeding setting everything up to have a radio broadcast, I still have
a few questions regarding icecast use.
First, latency. I have a setup on a LAN, where I can add audio files to
the stream, with a python script that automatically send the location of
the file to be played continuously. I wanted to measure the latency from
the moment when I sent ices2 a sound file, and the time it is being played.
With a clean refresh of my firefox, I experienced a latency of app. 15
secs. That's what I was expecting, but is it possible to reduce this
latency further.
Furthermore, must annoyingly, since the stream is playing continuously,
when I send new file to be played, the latency grows as the time goes. I
was able to measure latencies up to 1:30 or more after 20-30 mins of
continous playing. Is that normal, or is there some parameter to set up
in order to avoir this behavior.

Related to this, I read that it's possible to send directly raw PCM to
icecast when live streaming from the audio card input. Is it possible to
send raw PCM files to icecast in the same way ? I haven't find any
relevant information on this point. It would be neat, since I use of
software that outputs raw PCM files, but I need to convert them to ogg
before sending them to ices. As I understand it, if sent PCM audio,
icecast achieves the conversion on its own, so I wonder also if it
reduces latency to send it raw PCM or does not make much difference.

Last thing, what are the requirements in terms of clients. It seems not
all browsers react in the same way, same with audio players. Is there a
spec list of which software versions are needed to listen to latest
icecast2/ices2 streams.

Sorry for adding my fuzzy thoughts altogether.
Cheers

Sylvain


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