Icecast - Dec 2004 - Low-bitrate audio encode/stream application

I am totally new to icecast, and would appreciate a pointer in the right 
direction. My application is to encode audio (at the linux server) at a low 
bit rate, say ~16 kbps, for transmission to a decoder at another location. 
The audio source will be bandlimited (basically voice grade circuit such as 
you'd find in a telephone application.) The decoder end (connected via a 
TCP/IP session) would be a Windows CE 3.0 machine which may be limited to 
MP3 decode format. I've looked through what documentation I could find on 
icecast and haven't seen anything that tells me how to characterize the 
audio encoding rules (how do you pick 16 kbps, 32 kbps, etc., stereo, mono, 
etc.?) Anyway, a pointer to the correct documentation resource would be 
greatly appreciated.

Tks,

Dave
wb0gaz@hotmail.com

On Wed, Dec 22, 2004 at 02:28:18PM -0700, david feldman wrote:
> I am totally new to icecast, and would appreciate a pointer in the right 
> direction. My application is to encode audio (at the linux server) at a low
> bit rate, say ~16 kbps, for transmission to a decoder at another location. 
> The audio source will be bandlimited (basically voice grade circuit such as
> you'd find in a telephone application.) The decoder end (connected via
a
> TCP/IP session) would be a Windows CE 3.0 machine which may be limited to 
> MP3 decode format.
> I've looked through what documentation I could find on 
> icecast and haven't seen anything that tells me how to characterize the
> audio encoding rules (how do you pick 16 kbps, 32 kbps, etc., stereo, mono,
> etc.?) Anyway, a pointer to the correct documentation resource would be 
> greatly appreciated.
There are actually two pieces to this. Icecast itself is a server. It 
reflects streams from so-called 'source clients' to listening clients. 
It's in the source client that you set the encoding parameters. Ices is 
probably the best thing to use on linux, but there are others. See 
http://icecast.org/ices.php and http://icecast.org/3rdparty.php for 
links and associated howtos.

BTW, if you're actually doing voice over your very-low-bandwidth 
connection, you might consider our speex codec. It's designed 
specifically for speech and will in general do a much better job than 
vorbis or mp3 below 32 kbps. http://speex.org/

HTH,
 -r

Thanks Ralph,

speex is also interesting, and it will be for speech content, however, the 
listener side will be limited to generic CODEC (I don't want to port 
software to the CE machine, but rather use the existing older audio 
decoder(s) present there).

Anyway, this is good info, and I'll do some further reading.

Dave
>From: Ralph Giles <giles@xiph.org>
>To: david feldman <wb0gaz@hotmail.com>
>CC: icecast@xiph.org
>Subject: Re: [Icecast] Low-bitrate audio encode/stream application
>Date: Wed, 22 Dec 2004 13:51:28 -0800
>
>On Wed, Dec 22, 2004 at 02:28:18PM -0700, david feldman wrote:
>
> > I am totally new to icecast, and would appreciate a pointer in the
right
> > direction. My application is to encode audio (at the linux server) at
a
>low
> > bit rate, say ~16 kbps, for transmission to a decoder at another 
>location.
> > The audio source will be bandlimited (basically voice grade circuit
such
>as
> > you'd find in a telephone application.) The decoder end (connected
via a
> > TCP/IP session) would be a Windows CE 3.0 machine which may be limited
>to
> > MP3 decode format.
>
> > I've looked through what documentation I could find on
> > icecast and haven't seen anything that tells me how to
characterize the
> > audio encoding rules (how do you pick 16 kbps, 32 kbps, etc., stereo, 
>mono,
> > etc.?) Anyway, a pointer to the correct documentation resource would
be
> > greatly appreciated.
>
>There are actually two pieces to this. Icecast itself is a server. It
>reflects streams from so-called 'source clients' to listening
clients.
>It's in the source client that you set the encoding parameters. Ices is
>probably the best thing to use on linux, but there are others. See
>http://icecast.org/ices.php and http://icecast.org/3rdparty.php for
>links and associated howtos.
>
>BTW, if you're actually doing voice over your very-low-bandwidth
>connection, you might consider our speex codec. It's designed
>specifically for speech and will in general do a much better job than
>vorbis or mp3 below 32 kbps. http://speex.org/
>
>HTH,
>  -r

Hi:

Just curious, do we have any/many speex-enabled source clients and players?

Geoff.


-- 
Geoff Shang <geoff@hitsandpieces.net>
Phone: +61-418-96-5590
MSN: geoff@acbradio.org

Make sure your E-mail can be read by everyone!
http://www.betips.net/etc/evilmail.html

Please avoid sending me Word or PowerPoint attachments.
See http://www.fsf.org/philosophy/no-word-attachments.html

Hi David,

trying to put pieces together...
judging by your email-adress you must be an radio amateur.
lets try an "educated guess" ;)

hope you're not going to try running digimodes through that... ;)

Short wave audio should be fine. I use darkice myself for exactly that 
purpose: remote RX at dl0td while travelling around europe.

One thing you should remember is: there is a considerable delay you wont 
be able to reduce below a minimum (depending on network and client 
software). This makes tuning bit harder on ssb.

Oh before i forget: there is a mediaplayer capable of streaming mp3 and 
ogg/vorbis for WinCE (HPC/PPC). I've been using it for quite some time 
before i switched towards embedded linux. It is a bit tricky to get it 
running (you have to prepare a special playlist file containing the 
stream adress in a weird char encoding)
Hopefully this is fixed by now. would make it more useable. ;)
you should be able to find it either at corecodec.com or while looking 
for pocket-divx (its an descendant of the abandoned pocket-divx 
sourcecode).

bitrates can be pushed quite low while using ogg/vorbis. quality -1 at 
22kHz mono should already give you around 20kbit or so with drops to 
nearly zero when there is very low noise-level and no signal. A downside 
could be increased time-shift due to buffers filling up slowly.

vy 73 es merry x-mas es happy nw yr de Thomas, dm8tbr