Subject: [avtext] Comments on draft-ietf-avtext-client-to-mixer-audio-level-02

From: Magnus Westerlund <[email-masked]>
Date: Wed, 22 Jun 2011 15:43:06 +0200

Hi,

I have reviewed this draft and have a few comments.

1. Section 3.
"The two-byte header defined in RFC 5285 [RFC5285] may also be used."

I think that it should be stated up front that header extensions per
definitions can be used with either of the header formats. In addition I
think one needs to separate a bit clearer what is framework and what is
the new parts.

2. Section 3. I think the dBov definition needs to be really clear. Yes,
the convention is amplitudes are squared when doing dB calculation. But
it is not clear if this is done for the single highest value in the
measured range, or if it is done as an average over the measured range.
Please provide a definition or a reference.

3. Section 5:
  "The audio level for digital silence, for example for a muted audio
   source, MAY be represented as 127 (-127 dBov), regardless of the
   dynamic range of the encoded audio format."

I don't like this MAY. To me it appears to only complicate
implementations. Either you mandate the behavior so that one can trust
sources muted by the application to always carry value 127. Or one
anyway need to have noise level detector so that one can determine when
there is signal above the noise level. One may have to have that anyway,
but I think we should consider if we want clear MUTED indication here or
not.

4. Section 3:
   In addition, a flag bit (labeled V) indicates whether the encoder
   believes the audio packet contains voice activity (1) or does not
   (0).  The voice activity detection algorithm is unspecified and left
   implementation-specific.

Would it be of interest to have an signalling parameter for an
implementation to indicate its algorithm?

5. Section 8.2:
I think both the encrypted header extension and the VBR audio is likely
normative references as they either is recommend solution or a
description of the issue.

Cheers

Magnus Westerlund

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