[icecast] *Real* real time streaming (no delay/latency)?
nettings at folkwang-hochschule.de
Wed Feb 4 23:52:28 PST 2004
one problem apart from icecast is that tcp/ip over ethernet does not
guarantee *when* your packets will arrive, or even in what order.
while the chances are good that it works rather quickly, you can't
sue anyone if it doesn't ;)
but once the network becomes congested, you are in trouble. if the
network between your two locations is one cable, not shared, no
hubs, it might work. but if it's part of a larger net with lots of
background traffic, i wouldn't rely on it.
transmitting audio with low latency over networks has been a
frequent topic on the linux-audio-dev list, because it would be ever
so cool if it worked (think clusters of machines for huge
synthesizers or effects racks).
there have been some suggestions on how to do it, you may want to
search the archive at http://linuxaudiodev.org/archive.php3, but so
far the results have been mixed :(
i can't think why you would want to use an encoded stream though.
there's many more stages to tune for latency, and you don't get the
original signal to your fm transmitter. why not stream the digital
out of your radio desk? or do you have to pay per byte?
<p>Jørgen Elgaard Larsen wrote:
> 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
> 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.
> 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?
> 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.
> 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.
> Hope you can help,
> Jørgen Elgaard Larsen
> IT Manager
> University Radio of Copenhagen
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