Subject: [apps-discuss] Applications Area Directorate Review of draft-ietf-payload-vp8-08

From: Bert Greevenbosch <[email-masked]>
Date: Fri, 14 Jun 2013 06:12:02 +0000

Document: draft-ietf-payload-vp8-08
Title: RTP Payload Format for VP8 Video
Reviewer: Bert Greevenbosch
Review Date: 14 June 2013
Summary: Some minor issues and nits.

Major Issues:

none

Minor Issues:

(1) P.10: "KEYIDX: ... KEYIDX SHOULD start on a random number"
-> Why is this recommended?
 
(2) P.10: "In the case of a key frame the remaining 7 octets are considered to be part of the remaining payload in this RTP format."
-> Is this different from the case of an interframe? Where lies the difference?

(3) P.10: "Note that the header is present only in packets which have the S bit equal to one and the PartID equal to zero in the payload descriptor. Subsequent packets for the same frame do not carry the payload header."
-> What happens if the packet with the payload header was lost?
-> Is the rest of the partition still usable or is it completely useless? 
-> If it still can be usable, wouldn't it need the size information?

(4) The specification uses dynamic RTP payload numbers. This can be deduced from example 6.2.1.1 on P.23. However, it would be good to say this explicitly.

Nits:

(5) P.9: "M: ... If set the PictureID field MUST contain 16 bits else it MUST contain 8 bits including this MSB, see PictureID."
-> This is unclear in figure 2.

(6) P.9: "TID: ... The TID/KEYIDX octet MUST be present when either the T bit or the K bit or both are equal to 1, and MUST NOT be present otherwise."
P.9: "Y: ... The TID/KEYIDX octet MUST be present when either the T bit or the K bit or both are equal to 1, and MUST NOT be present otherwise."
P.10: "KEYIDX: ... The TID/KEYIDX octet MUST be present when either the T bit or the K bit or both are equal to 1, and MUST NOT be present otherwise."
-> These three sentences are superfluous in the light of
P.8: "T: TID present. When set to one, the OPTIONAL TID/KEYID octet MUST be present. ... If neither T nor K is set to one, the TID/KEYIDX octet MUST NOT be present" and
P.8: "K: KEYIDX present. When set to one, the OPTIONAL TID/KEYIDX octet MUST be present."

(7) In section 4.5.3, it would be good to indicate how L depends on size N.

(8) I think in which order the fragments need to be re-assembled depends on the RTP sequence number. Should that be stated somewhere in the example in section 4.5.4?