Subject: [siprec] Requirements: Aligning RTP streams

From: Peter Musgrave <[email-masked]>
Date: Sun, 25 Apr 2010 15:38:31 -0400

Hi,

In reviewing the requirements it is not clear to me that if a
recording has a video and audio RTP stream that these can be aligned
at the recorder. (In general the recorder will need the RTCP sender
reports for each stream so the NTP time/timestamp info can be used to
align the video and audio for playback.)

Do we need an explicit requirement to indicate that it must be
possible to align separate media streams or is this viewed as obvious,
or as just the details for REQ-11?

Perhaps we could amend REQ-11 to say: "The RS must be able to
synchronize associated media streams from the same source (e.g. audio
and video). "

Regards,

Peter Musgrave

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From: Brian Rosen <[email-masked]>
Date: Mon, 26 Apr 2010 07:28:36 -0400

<as individual>
Don't even multiple audio streams have to be time aligned (albeit with less
accuracy, probably)?  I think it's probably a requirement to send time
stamps.

Brian

On 4/25/10 3:38 PM, "Peter Musgrave" <[email-masked]> wrote:

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From: Peter Musgrave <[email-masked]>
Date: Mon, 26 Apr 2010 07:36:42 -0400

Hi,

Yeah - good point. Especially an issue when we record the unmixed
streams from a call.

[Implementation wise - this means recording timestamps in the RTP flow
as well as the sender reports (which allow timestamps to be referenced
to NTP time). If the streams are from different sources the NTP
alignment will never be perfect - but should be good enough.]

Peter Musgrave