Re: Issue 160: WebRTC 1.0 compatibility: support for p-time

To clarify:

RTCCodecCapability.maxptime is a capability of the decoder/receiver but not of the encoder/sender. RTCCodecParameters.maxptime is a setting of encoder/sender but not of the decoder/receiver.

As a result, peers can exchange the maxptime capability of their decoders, and then set the maxptime setting of their encoders appropriately.

-Robin

On January 5, 2015 at 4:00:27 PM, Bernard Aboba (bernard.aboba@microsoft.com) wrote:

Peter Thatcher said:

 

“Should we just put this in RtpCodecParameters.parameters, or should we have a specific RtpCodecParameters.ptime? Or do we want .minptime and .maxptime?”

 

[BA]  Here is a summary of ptime support in various codecs:
https://www.ietf.org/mail-archive/web/rtcweb/current/msg11485.html

And here is the summary of the recommendations from https://tools.ietf.org/html/draft-ietf-rtcweb-jsep:

Section 5.2.1 (Intial Offers):
Each m= section MUST include the following attribute lines:
...
o For each supported codec, "a=rtpmap" and "a=fmtp" lines, as
specified in [RFC4566], Section 6. For audio, the codecs
specified in [I-D.ietf-rtcweb-audio], Section 3, MUST be be
supported.

o If this m= section is for media with configurable frame sizes,
e.g. audio, an "a=maxptime" line, indicating the smallest of the
maximum supported frame sizes out of all codecs included above, as
specified in [RFC4566], Section 6.

As noted in Magnus' summary, there are codec-specific ptime capabilities and settings that could be discovered in RtpCodecCapability.parameters and set in RtpCodecParameters.parameters.  However, since the JSEP draft requires " an "a=maxptime" line, indicating the smallest of the maximum supported frame sizes out of all codecs included" it would be useful to have RtpCodecCapability.maxptime and RtpCodecParameters.maxptime so as to make it possible to discover a codec's maxptime, configure it and then compute the smallest of the maxptime values for all codecs.

A proposed resolution would look like this:

 

partial dictionary RTCRtpCodecCapability {

          unsigned long  maxptime;

}

 

 

partial dictionary RTCRtpCodecParameters {

          unsigned long  maxptime;

}