Dear Ali,
Thank you for the comments.
Please see inline.
Boudani Ali wrote:
Hello,
I read the two drafts. Before going to the IESG, It will be better if
the authors clarify some issues.
Here are my comments:
1- How can we identify the packets belonging to the same Codestream
(frame) (especially when using multiple RTP sessions). Don't you
think
that we need to add a frame_id identifier?.
RTP timestamp can be used for that purpose.
2- In section 4.1 of Draft-ietf-avt-rtp-jpeg2000-15.txt: you
consider 90
KHz for the Timestamp, this is not enough for professional video
using
JPEG2K: isn't better to leave this to the implementers?
RTP timestamp is a presentation timestamp.
Same frame has same rtp timestamp and timestamp difference
between frames is constant. Therefore 90KHz timestamp is enough.
How many clock rate would you consider for RTP timestamp ?
If there is a strong incentive, I feel no reluctance to
select different clock using rtpmap.
3- Adding a payload header is an overhead, so smaller payload header
size is better. Now, why do we need "T" and "tile number" fields? You
said that many tiles may exist in the same packet, so in this case no
meaning of "tile number" and "T" fields?
As you pointed, "tile number" and "T" may not be necessary when
many tiles exists in the same packet, but if no tile header exists
in a packet, which may be more possible, "tile number" and "T"
is needed for receiver to clarify which tile the codestream
is belonging to.
4- Is the tp (type) field necessary?. The RTP payload has already the
payload type (PT) and we can use it instead of tp? If not this
information can be communicated out of band and can be optional as
the
width and height in section 8.1!
We believe it is necessary because the receiver identify whether
the received codestream is odd or even field's.
"tp" can be used for determining the reciever's action.
For example, if it receives odd field continuously, it can interpolate
even field in some way, or simply discard the duplicated odd field.
5- Why do you use the fragment offset?. Isn't (for one RTP
session) the
sequence number of the RTP packet enough?
When using multiple RTP sessions for layered video, the parser that
extracted the data for a particular layer (for a particular RTP
session)
may be transmitted out of band also (the index file is stored
either as
a separate file or as meta-data). The index file is transmitted to
the
receiver also, so the receiver can rebuild the codestream.
When using multiple RTP session for layered video,
JPEG2000 codestream may be split with interleaving.
For example,
Codestream
+----------+----+----+----+----------+----+----+----+----------+----
|Tile 0 Hdr| L0 | L1 | L2 |Tile 1 Hdr| L0 | L1 | L2 |Tile 2 Hdr| ...
+----------+----+----+----+----------+----+----+----+----------+----
RTP 1
+----------+----+ +----------+----+ +----------+----
|Tile 0 Hdr| L0 | |Tile 1 Hdr| L0 | |Tile 2 Hdr| L0
+----------+----+ +----------+----+ +----------+----
RTP 2 +----+ +----+
| L1 | | L1 | ....
+----+ +----+
RTP 3 +----+ +----+
| L2 | | L2 | ....
+----+ +----+
In that case,
interleaved codestream doesn't alwasy arrive at the receiver
in original order.
Fragment offset helps the receiver to rebuild the codestream.
Also, if the fragment offset exist, the receiver need less
memory because it doesn't need de-intgerleave buffer to
rebuilt codestream. It can use same memory space to rebulit it.
6- Do we really need to have an MHD flag? The size of main header
may be
about 300 bytes so is there any chance that this packet will be
fragmented?
Typical main header may be at most 300 bytes long, but if some
JPEG2000
coding options are used, it may be longer.
So MHF flag is neccessary for such situation.
7- For the priority field use (the example in section 1.3.1): the
receiver can select which parts of the codestream to decode without
using the priority field. It can rebuild the codestream and
extract the
parts to decode by reading the main header?.
Main header contains the progression order information, but it doesn't
include the address information (start position) of each priority
level.
Priority field helps the receiver to select the codestream to put into
decoder easily. Without priority field, the receives needs more memory
to rebuild it and has to parse the codestream.
Best Regards,
Futemma
Cheers,
Ali
-----Original Message-----
From: Colin Perkins [mailto:csp at csperkins.org]
Sent: lundi 14 mai 2007 13:59
To: IETF AVT WG
Cc: Roni Even; Tom-PT Taylor
Subject: [AVT] Working group last call: JPEG-2000 payload format
This is to announce a working group last call on the RTP Payload
Format for JPEG-2000:
http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-
jpeg2000-15.txt
http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-jpeg2000-
beam-06.txt
Please send any final comments on these drafts to the <avt at ietf.org>
mailing list by 28 May 2007. If no substantive comments are received
by that time, we will ask the IESG to consider these drafts for
publication as Proposed Standard RFCs.
Note that there is declared IPR on the "beam" draft:
https://datatracker.ietf.org/public/ipr_detail_show.cgi?ipr_id=697