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RE: Issue 1021: get/setParameters does not have a parameter for packetization interval

From: Bernard Aboba <Bernard.Aboba@microsoft.com>
Date: Wed, 22 Feb 2017 19:44:53 +0000
To: Varun Singh <varun@callstats.io>
CC: "public-webrtc@w3.org" <public-webrtc@w3.org>
Message-ID: <SN1PR21MB0014B2D50BC11519CC3A6627EC500@SN1PR21MB0014.namprd21.prod.outlook.com>
Varun said: 

"I'd like to be able to change ptime for an audio codec, if I am able
to set it, it would be reasonable to know what is the maxptime and to
not set it higher."

[BA]  Looking at JSEP Section 5.2.1 (initial Offers): 

   o  If this m= section is for media with configurable durations of
      media per packet, e.g., audio, an "a=maxptime" line, indicating
      the maximum amount of media, specified in milliseconds, that can
      be encapsulated in each packet, as specified in [RFC4566],
      Section 6.  This value is set to the smallest of the maximum
      duration values across all the codecs included in the m= section.

Section 5.3.1 (Initial Answers) says: 

   o  If this m= section is for media with configurable durations of
      media per packet, e.g., audio, an "a=maxptime" line, as described
      in Section 5.2.

Section 5.7.2 (Media Section Parsing) says: 

   o  If present, a single "a=ptime" line MUST be parsed as described in
      [RFC4566], Section 6, and its value stored.

   o  If present, a single "a=maxptime" line MUST be parsed as described
      in [RFC4566], Section 6, and its value stored.

Section 5.9 (Applying a Remote Description) says: 

      *  If the media section is of type audio:

         +  For any specified "ptime" value, configure the available
            media formats to use the specified packet size.  If the
            specified size is not supported for a media format, use the
            next closest value instead.

[BA] Together this suggests that a single value of maxptime or ptime is provided per m-line.  

However, currently the object model only provides the ability to expose capabilities such as maxptime at codec-level granularity within RTCRtpCodecCapability or settings such as ptime at codec-level granularity within RTCRtpCodecParameters.
Received on Wednesday, 22 February 2017 19:45:31 UTC

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