Subject: [AVT] draft-ietf-avt-mpeg4-simple-04.txt and video packets

From: "Julien Boeuf" <[email-masked]>
Date: Tue, 12 Nov 2002 15:19:39 +0100

Hi,

I'm trying to define a new mode in this draft for transport of MPEG-4 video
using video packets which are mapped to RTP packets.
Here's my problem: I'd like to put the AU numbers in the RTP Packets
otherwise the client won't be able to tell if it has lost a complete AU or
just some video packets as shown in the example below:

Server    Client
AU3
    VP1 -> VP1
    VP2 -> VP2
    VP3 -> VP3

AU4
    VP4 -> LOST
    VP5 -> LOST

AU5
    VP6 -> LOST
    VP7 -> VP7

AU6
    VP8 -> VP8
...

I wish I could use the AU-Index field in the AU-Header part but it is said
that this one is associated with the associated Access Unit (fragment) and
if I understand well, in my case, this one is redundant with the Sequence
Number of the packet. Am I right? If so, I think I can use the
auxiliary-data to do what I want.

I have another question regarding the use of this draft for scalable video.
It would be nice, I think, to have another SDP Parameter which indicated the
layer of the video for a particular rtpmap. Would this be possible?

Thanks a lot,

    Julien.

_______________________________________________
Audio/Video Transport Working Group
[email-masked]
https://www1.ietf.org/mailman/listinfo/avt

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From: Colin Perkins <[email-masked]>
Date: Tue, 12 Nov 2002 10:13:26 -0500

>layer of the video for a particular rtpmap. Would this be possible?

It's implicit in the SDP port list, so there shouldn't be a need for an
additional parameter.

Colin

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From: "Julien Boeuf" <[email-masked]>
Date: Tue, 12 Nov 2002 23:03:36 +0100

Hi Colin,

| It's implicit in the SDP port list, so there shouldn't be a need for an
| additional parameter.
Sorry, I'm still confused. Can you give me an example?

Thanks,

    Julien.

---

From: Colin Perkins <[email-masked]>
Date: Tue, 12 Nov 2002 17:13:13 -0500

>Sorry, I'm still confused. Can you give me an example?

From the SDP spec:

    For applications where hierarchically encoded streams are being sent
    to a unicast address, it may be necessary to specify multiple
    transport ports.  This is done using a similar notation to that used
    for IP multicast addresses in the ``c='' field:

         m=<media> <port>/<number of ports> <transport> <fmt list>

    In such a case, the ports used depend on the transport protocol.
    For RTP, only the even ports are used for data and the corresponding
    one-higher odd port is used for RTCP.  For example:

         m=video 49170/2 RTP/AVP 31

    would specify that ports 49170 and 49171 form one RTP/RTCP pair and
    49172 and 49173 form the second RTP/RTCP pair.  RTP/AVP is the
    transport protocol and 31 is the format (see below).

The first layer goes on the lowest numbered RTP port pair, the other layers
follow sequentially. 

Colin