Re: [rtcweb] Working group last call for draft-ietf-rtcweb-audio
Roman Shpount <roman@telurix.com> Tue, 26 January 2016 21:21 UTC
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Date: Tue, 26 Jan 2016 16:21:41 -0500
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From: Roman Shpount <roman@telurix.com>
To: Jean-Marc Valin <jmvalin@mozilla.com>
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Cc: "Cullen Jennings (fluffy)" <fluffy@cisco.com>, "rtcweb@ietf.org" <rtcweb@ietf.org>
Subject: Re: [rtcweb] Working group last call for draft-ietf-rtcweb-audio
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On Tue, Jan 26, 2016 at 3:26 PM, Jean-Marc Valin <jmvalin@mozilla.com> wrote: > The text below is what you propose for the rtcweb-audio draft? I > personally have no opinion on these events (see comment inline for > clarification though) so I'm happy to include that text if everyone > else is OK with it. > Yes, this is the text I am proposing for rtcweb-audio draft. > Generated events MUST have duration of no more than 6000 ms and no > > less than 40 ms with the recommended default duration of 100 ms for > > each tone. The gap between events MUST be no less then 30 ms with > > the recommended default duration of 70 ms. Event SHOULD start on a > > regular audio packet border and event and gap duration SHOULD be > > rounded up to the next regular audio packet border. > > > > During the time events are generated no audio SHOULD be sent for > > the same audio stream. When gaps between events are generated, > > silence and not the background audio SHOULD be sent using regular > > audio encoding. > > I think this would require a bit of clarification. What does "no > audio" mean here? Silence or no codec packets at all (in that case > what about PLC)? Also, keep in mind that any silence may not be > perfectly aligned with theoretical frame boundaries, due to look-ahead. > > First of all I was trying to copy all the normative tone duration information from W3C document to rtcweb-audio draft. Second, as far as "no audio" is concerned, what I mean here is that RFC4733 telephone-events are alternative audio encoding similar to CN (see https://tools.ietf.org/html/rfc4733#section-2.5.2.2). For RTP timestamp interval covered by telephone-event no non-event audio packets, such as Opus or G.711, should be present since they are redundant and cause interop problems. PLC does not apply here since remote gateways is supposed to generate audio based on the information in telephone-events packets. This is essentially the same requirement that end point should not send packets with two different audio encodings (i.e. send Opus and G.711 RTP packets) at the same time. This can work but can also cause interop problems. Packet boundaries of audio encoded using codecs such as G.711 or Opus should create a continuous stream as far as RTP timestamps are concerned with RFC 4733 telephone event packets unless discontinuous RTP is used. It should be possible to align decoded audio and telephone-events based on RTP timestamps. I also wanted to provide clarification for https://tools.ietf.org/html/rfc4733#section-2.5.1.2. This section says: A source has wide latitude as to how often it sends event updates. A natural interval is the spacing between non-event audio packets. (Recall that a single RTP packet can contain multiple audio frames for frame-based codecs and that the packet interval can vary during a session.) Alternatively, a source MAY decide to use a different spacing for event updates, with a value of 50 ms RECOMMENDED. I am proposing that WebRTC should recommend that sending telephone-event packet at natural interval between non-event audio packets is strongly preferred. Also, blocking input audio for a short period of time after telephone-events are transmitted prevents a duplicate DTMF digit audio from being present in the encoded audio stream which some times happen due to microphone picking up audio feedback tones played by some DTMF keypad implementations. This also improves DTMF tone recognition by a receiving IVR system after audio stream passes through PSTN gateway since having background audio as a separator between DTMF digits can negatively affect some tone detection algorithms. Please let me know if you need more information. Regards, _____________ Roman Shpount
- [rtcweb] Working group last call for draft-ietf-r… Ted Hardie
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Ted Hardie
- Re: [rtcweb] Working group last call for draft-ie… Bernard Aboba
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Adam Roach
- Re: [rtcweb] Working group last call for draft-ie… Adam Roach
- Re: [rtcweb] Working group last call for draft-ie… Ted Hardie
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Ted Hardie
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Bernard Aboba
- Re: [rtcweb] Working group last call for draft-ie… Cullen Jennings (fluffy)
- Re: [rtcweb] Working group last call for draft-ie… Bernard Aboba
- Re: [rtcweb] Working group last call for draft-ie… Cullen Jennings (fluffy)
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Adam Roach
- Re: [rtcweb] Working group last call for draft-ie… Barry Dingle
- Re: [rtcweb] Working group last call for draft-ie… Bernard Aboba
- Re: [rtcweb] Working group last call for draft-ie… Matthew Kaufman
- Re: [rtcweb] Working group last call for draft-ie… Gunnar Hellström
- Re: [rtcweb] Working group last call for draft-ie… DRAGE, Keith (Keith)
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… DRAGE, Keith (Keith)
- Re: [rtcweb] Working group last call for draft-ie… Martin Thomson
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… DRAGE, Keith (Keith)
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Tim Panton
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Jean-Marc Valin
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount
- Re: [rtcweb] Working group last call for draft-ie… Jean-Marc Valin
- Re: [rtcweb] Working group last call for draft-ie… Roman Shpount