shithub: opus

--- a/doc/ietf/draft-valin-celt-rtp-profile.xml

+++ b/doc/ietf/draft-valin-celt-rtp-profile.xml

@@ -421,21 +421,24 @@

 </t>

<t>

-Several CELT-specific parameters can be given via the "a=fmtp:" directive.  The

-following parameters are defined for use in this way:

+CELT-specific parameters can be given via the "a=fmtp:" directive.

+Several parameters can be given in a single a=fmtp line provided

+that they are separated by a semi-colon. The following parameters

+are defined for use in this way:

 </t>

<t>

 <list style="empty">

-<t>frame-size: The frame size is the duration of each frame in samples. If more than one frame size is supported, a comma-separated list can be used. The default is 480.</t>

+<t>frame-size: The frame size is the duration of each frame in samples. If more than one frame size is supported, a comma-separated list can be used. It is possible to use "any" to denote that

+all even frame sizes are supported. The default is 480.</t>

 <t>mapping: Optional string describing the multi-channel mapping. </t>

 </list>

 </t>

-<t>Several CELT specific parameters can be given in a single

-a=fmtp line provided that they are separated by a semi-colon.</t>

+<t>Because the frame-size is not transmitted in-band, an SDP answer MUST

+contain only one frame-size, even if multiple frame sizes were offered.

+</t>

<t>

 The selected frame-size values MUST be even. They SHOULD be divisible by 8

@@ -444,7 +447,9 @@

 recommended. Implementations MUST support receiving and sending the default

 value of 480, and if the size 480 is supported it MUST be offered. Implementations

 SHOULD also support frame sizes of 256 and 512 since these are the ones that lead

-to the lowest complexity.

+to the lowest complexity. When frame sizes that are powers of two are supported,

+they SHOULD be listed first in the offer and chosen over non powers of two in the

+answer.

 </t>

<t>