[Speex-dev] rtp payload lenth

[Jean-Marc Valin]

Not sure what a payload of 75 bytes could be. Are you sure that doesn't
include the 12-byte RTP header? Other than that, maybe it's using
wideband (although there's nothing that corresponds exactly to 75 bytes.

If you send me the hexdump for one packet, I may be able to find out
what it is.

	Jean-Marc

Pawel Cyrta wrote:
> Hello to all speex developers,
> 
> I have question regarding payload length of narrowband speex in RTP.
> I were watching tcpdump of the xlite softphone and have found that
> it uses weird payload length namely 75 Bytes
> I went through various source and without success.
> 
> To be clear:
> For 8000Hz sample in 20 ms that is 160 samples per frame.
> This makes 50 frames per sec.
> 
> modes     bit-rate    8 kbit/s    (narrowband mode 3) = 20 bytes per frame
> 11 kbit/s (narrowband mode 4)  = 28 bytes per frame
> 15 kbit/s (narrowband mode 5)  = 38 bytes per frame
> 18,2 kbit/s (narrowband mode 6)  = 46 bytes per frame
> 24,6 kbit/s (narrowband mode 7)  = 62 bytes per frame
> 
> 
> And for VBR   frame size is from a set of {6,11,16,21,29,39}
> 
> So, X-lite uses 75 Bytes and this does not look as multiplication of 2
> frames.
> Additionally, timestamp between consecutive rtp frames is exactly 20ms, so
> this implies that this 75 Bytes is only one frame plus maybe bits of
> padding.
> 
> 
> Can one of you tell me what kind of mode this is?
> 
> Thank you in advance.
> 
> Pawel
> 
> ps. IMHO  some kind of table that I've shown should be included in RFC
> so in Table 1 in draft-ietf-avt-rtp-speex-03 there should be additional
> column.
> Namely frame size.
> 
> 
> 
>     
> Pawel Cyrta <pawel at cyrta.com <mailto:pawel at cyrta.com>>
> 
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