Speex dev - Aug 2004 - frame size

Joost Witteveen (joost@iliana.nl) wrote:
> 
> So, each UDP package with 20 bytes speex-data, we send:
> 
> 20 bytes speex
> 12 bytes ogg headers (and others?)
> 28 bytes UDP/IP headers (2 IP numerbers, 2 portnumbers, checksum, etc, etc)
> 
> and, if it goes over the phone, each package has a few ppp headers.
> 
> Am I overlooking something, or does this fixed frame size mean that
> the "8kbps" in reality means at least 24kbps?
> 
> Or is there something ohphone/gnomemeeting/etc can/should do to
> put more than one fram inside each UDP package?
Er, why would you be sending ogg headers in a VoIP scenario?  That's 
needless overhead.  Check out the Speex RTP format document at
http://www.speex.org/drafts/draft-herlein-speex-rtp-profile-00.txt.
Figure 1 and sections 3.2 and 5 show how to send multiple frames 
per packet.

In my VoIP program, I use my own protocol (for now) and each 
packet currently works out like this:

~5 bytes - PPP
20 bytes - IP
 8 bytes - UDP
 1 byte  - sequence number (my own)
~40-300 bytes - 4 Speex frames (VBR quality 6, wideband)

I send at a rate of 12.5 packets per second, putting 4 Speex frames 
in each packet.  This gives a total bandwidth usage of approximately 
7.4kbps to 33.4kbps, which I think is pretty good for high quality 
wideband, and it works on a dialup modem.

Anyway, putting just one frame in a packet is definitely going to 
kill you with packet overhead!  You have to compromise on latency.  
The frame size that Speex uses is small enough that you still have a 
fair amount of flexibility in determining how many samples you want 
to put in each packet.

Tom
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Je 2003/12/09(2)/13:12, Tom Grandgent skribis:
> Joost Witteveen (joost@iliana.nl) wrote:
> > 
> > So, each UDP package with 20 bytes speex-data, we send:
> > 
> > 20 bytes speex
> > 12 bytes ogg headers (and others?)
> > 28 bytes UDP/IP headers (2 IP numerbers, 2 portnumbers, checksum, etc,
etc)
> > 
> > and, if it goes over the phone, each package has a few ppp headers.
> > 
> > Am I overlooking something, or does this fixed frame size mean that
> > the "8kbps" in reality means at least 24kbps?
> > 
> > Or is there something ohphone/gnomemeeting/etc can/should do to
> > put more than one fram inside each UDP package?
> 
> Er, why would you be sending ogg headers in a VoIP scenario?  That's 
> needless overhead.  Check out the Speex RTP format document at
http://www.speex.org/drafts/draft-herlein-speex-rtp-profile-00.txt.
> Figure 1 and sections 3.2 and 5 show how to send multiple frames 
> per packet.
OK, thanks!
When both gnomemeeting and ohphone gave me no options to put more
than one frame in the packages, I apparently too quickly assumed
that it was impossible to do.

So now I guess gnomemeeting/ohphone need to be patched.
> In my VoIP program, I use my own protocol (for now) and each 
> packet currently works out like this:
> 
> ~5 bytes - PPP
> 20 bytes - IP
>  8 bytes - UDP
>  1 byte  - sequence number (my own)
> ~40-300 bytes - 4 Speex frames (VBR quality 6, wideband)
> 
> I send at a rate of 12.5 packets per second, putting 4 Speex frames 
> in each packet.  This gives a total bandwidth usage of approximately 
> 7.4kbps to 33.4kbps, which I think is pretty good for high quality 
> wideband, and it works on a dialup modem.
Yeah, that seems sensible.
The ppp phone line I plan to use it over doesn't offer much more than
20bps, so I guess I cannot use gnomemeeting/ohphone as is now:(.

Thanks,
joostje
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