Re: [codec] it MUST NOT exceed 1275 bytes?

"Benjamin M. Schwartz" <bmschwar@fas.harvard.edu> Mon, 25 July 2011 17:27 UTC

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Date: Mon, 25 Jul 2011 13:27:09 -0400
From: "Benjamin M. Schwartz" <bmschwar@fas.harvard.edu>
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To: Christian Hoene <hoene@uni-tuebingen.de>
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Subject: Re: [codec] it MUST NOT exceed 1275 bytes?
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On 07/25/2011 01:18 PM, Christian Hoene wrote:
> 1) What must not exceed 1275 bytes, the total length of the payload or the
> length of the last VBR frame?

The latter.  No Opus frame may ever exceed 1275 bytes.

> 2) What are the calculations behind 1275?

"The maximum representable size is 255*4+255=1275 bytes."

Because the first N-1 frames in a packet cannot have a size greater than
1275, it would be very strange if this were permitted for the final frame.
 An unbounded frame size would also unreasonably increase the minimum
computational performance required of a conformant decoder.

> 3) The requirement "Repacketization by gateways, conference bridges, or
> other software." is not listed in the requirements draft.

Indeed, but the codec has a great deal of useful functionality beyond what
is required in that draft.

> As I still believe
> in the end-to-end principle, I also do not see the need for this
> requirement.

Opus is intended for use beyond the internet.

 Why do you need an Opus-to-Opus gateway if have can have
> end-to-end or if you can use a TURN server? 

An Opus-to-Opus gateway is appropriate when an Opus stream is being moved
between different networks, including non-IP-based networks, with
different limits and overheads related to packet size and rate.

--Ben