[AVT] Comments on draft-ietf-avt-mpeg4-simple-06.txt
Colin Perkins <csp@csperkins.org> Wed, 08 January 2003 01:02 UTC
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To: jan.vandermeer@philips.com
cc: avt@ietf.org
From: Colin Perkins <csp@csperkins.org>
Date: Tue, 07 Jan 2003 20:00:41 -0500
Subject: [AVT] Comments on draft-ietf-avt-mpeg4-simple-06.txt
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Jan, I think the MPEG-4 payload format is in good shape now. I have a number of editorial comments below, mostly trying to tighten the language of the new interleaving section and clarifying some of the examples. Colin - Need to make it clear that the interleaving pattern at the bottom of page 7 is an example, and that other patterns are possible. Suggest changing "Assume that..." to "For example, if we assume that..." - The first paragraph of section 3.2.3.2 "Interleaving" is unclear. I suggest rewriting it as follows: Unless prohibited by the signalled mode, a sender MAY interleave Access Units. Receivers that are capable of receiving modes that support interleaving MUST be able to decode interleaved Access Units. (The last sentance of the original paragraph was redundant with the explanation that followed). - The second paragraph of section 3.2.3.2 starts "When a sender interleaves Access Units, then the transmitter needs to...". This could be rewritten as "When a sender interleaves Access Units, it needs to..." - The formula at the top of page 17 has a non-ASCII character, which does not display correctly. I assume it should be a minus sign? - I find the explanation of the "constantDuration" parameter in the three paragraphs following the formula on page 17 to be unclear. I suggest the following rewording: The MIME parameter "constantDuration" SHOULD be used to signal that Access Units have a constant time duration, see section 4.1. If the "constantDuration" parameter is present, the receiver can reconstruct the original Access Unit timing based solely on the RTP timestamp and AU-Index-delta. Accordingly, when transmitting Access Units of constant duration, the AU-Index, if present, MUST be set to the value 0. Receivers of constant duration Access Units MUST use the RTP timestamp to determine the index of the first AU in the RTP packet. The AU-Index-delta header and the signalled "constantDuration" are used to reconstruct AU timing. If the "constantDuration" parameter is not present, then Access Units are assumed to have a variable duration. In this case, the transmitter MUST use the AU-Index to encode the index information required for re-ordering, and the receiver MUST use that value to determine the index of the first AU in the RTP packet. The number of bits of the AU-Index field MUST be chosen so that valid index information is provided at the applied interleaving scheme, without causing problems due to roll-over of the AU-Index field. In addition, the CTS-delta MUST be coded in the AU header for each non-first AU in the RTP packet, so that receivers can place the AUs correctly in time. - Section 4.1 defines the "ConstantDuration" parameter, but the text refers to it as "constantDuration". They should be consistant. - In section 3.3.2, the draft should mention that the a=fmtp: line has been split for presentation in the RFC, and is actually a single long line. Also, "BIFSConfiguration()" should be replaced by an example of the hexadecimal string, and the text "BIFSConfiguration() is the hexadecimal string as defined in ISO/IEC 14496-1" replaced by "The hexadeciaml string in the 'config=' parameter is the result of the BIFSConfiguration() function defined in ISO/IEC 14496-1", or similar. [Similar comments apply to the examples in the other modes] - In section 3.3.3, the draft might say "Interleaving MUST NOT be used with this mode" instead of "there is no support for interleaving". A similar comment applies to section 3.3.4 where "optional interleaving" could be "OPTIONAL interleaving". - In section 3.3.5, "frames MUST not be fragmented" -> "...MUST NOT..." _______________________________________________ Audio/Video Transport Working Group avt@ietf.org https://www1.ietf.org/mailman/listinfo/avt
- [AVT] Comments on draft-ietf-avt-mpeg4-simple-06.… Colin Perkins