Subject: RE: [AVT] I-D ACTION:draft-ietf-avt-rtp-ac3-01.txt

From: "Link, Brian" <[email-masked]>
Date: Mon, 3 Jan 2005 10:39:27 -0800

Greetings and Happy New Year,

As the quoted announcement states, I have revived the RTP payload format
I-D for AC-3. I have made a number of changes to take into account
comments that had previously been offered, to simplify the draft, and to
add some time code functionality that is used in some products.

An industry consortium called the Digital Living Network Alliance (DLNA)
plans to stream AC-3 over RTP in some of its home networking
applications. In order for DLNA to reference the payload format in this
document (instead of publishing their own), it will need to be published
in a relatively short time.  I will very much appreciate it if
interested people could review and comment on this I-D to move it along
quickly.

Best regards,
Brian

---
Brian Link
Dolby Laboratories, 100 Potrero Ave., San Francisco, CA 94103
phone: 415-558-0324  fax: 415-863-1373
email: [email-masked]   alt email: [email-masked]

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Sent: Wednesday, December 29, 2004 12:36 PM
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Subject: [AVT] I-D ACTION:draft-ietf-avt-rtp-ac3-01.txt

A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the Audio/Video Transport Working Group of
the IETF.

	Title		: RTP Payload Format for AC-3 Streams
	Author(s)	: J. Flaks, et al.
	Filename	: draft-ietf-avt-rtp-ac3-01.txt
	Pages		: 9
	Date		: 2004-12-29
	
This document describes an RTP payload format for transporting AC-3
encoded audio data.  AC-3 is a high quality, multichannel audio coding
system used in US HDTV, DVD, cable and satellite television and other
media.  The RTP payload format as presented in this document includes
support for data fragmentation.

A URL for this Internet-Draft is:
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From: Colin Perkins <[email-masked]>
Date: Sat, 15 Jan 2005 14:57:21 +0000

Brian,

> interested people could review and comment on this I-D to move it along

Mostly this looks good, although I have a couple of technical concerns:

  - Including a SMPTE time code in each packet is unusual, and redundant
    with the RTP timestamp (which is mapped to an NTP-format timestamp 
via
    RTCP SR packets) in many cases. Is it possible to use the RTP 
timestamp
    instead, possibly with a signalled mapping from SMPTE time code to an
    NTP format timestamp in the SDP during session setup?

  - The second is that the definition of "ptime" is unusual. I think it
    would be better as:

	ptime: The duration of time in milliseconds represented by each AC-3
	frame. This corresponds to the duration of each RTP packet in cases
	where fragmentation is not used.

    without trying to define what it means for fragments.

  - Finally, the draft should define how SDP is used in offer/answer 
mode to
    negotiate parameters. It should also describe how the MIME 
parameters are
    copied into the SDP (section 5.1 of RFC 3557 is a good example).

I've also sent a few minor editorial comments privately.

Colin