[vorbis] Ogg streaming on low bandwidth

[Stan Seibert]

On Thu, 2003-08-14 at 00:50, engdev wrote:
> Was wondering if any gurus could tell me if it is possible to stream
> Ogg on very low bandwidth links (for example satellite phone) where
> the expected bandwidth would almost certainly be less than 19Kbps, and
> probably more like 10Kbps.

For testing how low Vorbis can go, you don't need a full client/server
setup at first.  I did some fiddling using sox and oggenc (command line
tools often found on Linux systems, but available for windows as well). 
You could also use an audio editor that lets you resample audio and mix
down a stereo file to mono along with OggdropXP to do the Vorbis
encoding.

I took a track I had ripped from CD and used sox to resample and mix it
down to 8 kHz mono:

ox test.wav -r 8000 -c 1 test8kHz.wav resample

 I then encoded it using quality -1, the lowest VBR quality setting the
current encoder allows:

oggenc -q -1 test8khz.wav

The resulting file was 10.9 kbps, but without any bitrate management, so
there were bitrate spikes that might not be good for your application. 
The result was bad but livable, though I've never heard MP3 at this low
of a bitrate, so I have no point of reference.

Harder limits can be achieved with managed bitrates.  With:

oggenc --managed -M 10 test8khz.wav

I got a file with the bitrate capped at 10 kbps (but no explicit minimum
or average requested).  Not surprisingly, the encoder used every bit
possible under these constraints, resulting in a file with an average 
bitrate of 10 kbps.  In comparing the VBR with the managed bitrate
version, you can definitely hear the points where the encoder jumped the
bitrate up in the quality -1 encoding to prevent a particularly bad
artifact, but the managed bitrate version had to let through.

Incidentally, I found that an average bitrate of 8.3 kbps was the lowest
I was able to push the encoder to:

oggenc --managed -b 8 test8khz.wav

(That sets the average bitrate but not the min or max)

Anything lower and oggenc informed me that the bitrate parameters were
invalid.


---
Stan Seibert

<p>--- >8 ----
List archives:  http://www.xiph.org/archives/
Ogg project homepage: http://www.xiph.org/ogg/
To unsubscribe from this list, send a message to 'vorbis-request at xiph.org'
containing only the word 'unsubscribe' in the body.  No subject is needed.
Unsubscribe messages sent to the list will be ignored/filtered.