Re: [AVT] I-D ACTION:draft-ietf-avt-rtp-speex-01.txt

[Randell Jesup <rjesup at wgate.com>]

Aymeric Moizard <jack at atosc.org> writes:
>> Section 3.3: "Sampling rate values of 8000, 16000 or 32000 Hz MUST be
>> used. Any other sampling rates MUST NOT be used" is confusing. Better to
>> say "The sampling rate MUST be either 8000 Hz, 16000 Hz, or 32000 Hz".
>
>I agree.

The rate from rtpmap is not (necessarily) the sampling rate (witness
video); it's the rate for timestamp values, and typically (not always) will
be an integer multiple of the sampling rate or lowest common multiple of
the sampling rates, more or less.  I would dislike having the rtpmap rate
be a true codec parameter; there may be reasons for using values other than
the hardware sample rate.

Since another message indicated that the encoding could change on a
per-packet level (whether signalled in-bitstream and/or by payload value
change), it may make sense to use 32000 for the timestamp rate always.  It
is *really* problematic when the timestamp rate changes when you switch
payloads.  The only other value I can see making sense would be 8000, and
then only if you wanted to make it easier to switch between speex and
things like G.711 on the fly.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
rjesup at wgate.com
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)


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