[speex-dev] frame size
tgrand at canvaslink.com
Tue Dec 9 10:06:06 PST 2003
Joost Witteveen (joost at 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
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.
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