[icecast] *Real* real time streaming (no delay/latency)?

Jørgen Elgaard Larsen maillistparticipant at elgaard.net
Thu Feb 5 01:55:08 UTC 2004


Does anyone have experience with _real_ real time streaming - i.e. with 
very little delay/latency?

I need to stream from point A to point B in near-CD quality via a 100 
Mbit network. That is easily done using icecast. But here is the tricky bit:

I want as little delay in the signal as possibble - preferrably below 50ms!

I have made a test setup encoding on and serving from an 800 MHz Pentium 
II with debian GNU/Linux, icecast 2 and IceS 2. That gave me a delay of 
1 or 2 seconds. I need it to be lower.

<p>I have seen hardware that will do the same with only a 30 ms delay. Is 
that possible at all with icecast - even on a fast machine? Has anyone 
tried it? Has anyone made measurements on it?

Bandwith is (almost) no problem. Would it be possible to avoid delay 
somehow using another format (e.g. flac)? And would that work with icecast?

Is there any other software, I should look at?

<p>I have also wondered if it would help to get a sound card with hardware 
support for MP(2|3) encoding. They exist, but do anyone know of one that 
has a Linux driver? I know that it will probably need some additions to 
IceS, but I don't mind getting  my hands dirty...

Any help or thoughts would be greatly appreciated.

<p><p><p><p>A bit about my project for the curious:

I work at a student radio station. Our FM transmitter is located some 3 
km's from our studio, and right now we pay quite a lot for a analog 
leased line to transport our air signal from our studio to the transmitter.

Fortunately, there is a 100 Mbit IP network between us and the building 
on which the transmitter is located (most of the way it's actually 
gigabit). We would like to use that IP network to transport the signal 
from our studio to the transmitter.

We use the air signal from the transmitter for control listening and for 
playing around us when we broadcast from outside our studio (from dorms 
or different parts of the university). Also, we use the air signal as 
headphone feed for our announcers. All that is almost impossible with a 
huge delay on the signal (by huge I mean in the order of seconds).

Anything above 90 ms delay is useless for our purpose.

I have ad an offer on some hardware that can do the trick, but for the 
price they are asking, I could easily buy 5 or 6 top-of-the-range PC's 
with decent sound cards. Also, the PC solution would be more flexible, 
allowing us to control our RDS signal and so on.

Besides working at the radio station, I am also a graduate student at 
Dept. of Computer Science at the University of Copenhagen, so I wouldn't 
mind writing a bit of code, if it was necessary.

<p><p>Hope you can help,

<p><p>Jørgen Elgaard Larsen
IT Manager
University Radio of Copenhagen

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