Subject: Re: [AVT] SDP Negotiation based on Profile-Level-Id

From: Kyunghun Jung <[email-masked]>
Date: Wed, 10 Sep 2008 07:53:29 +0000 (GMT)

Dear AVT experts:

We are happy to see the many comments
that will help the introduction of “a=imageattr”

First, let us consider the
question from Mr. Wang Ye-Kui.

Just a question
with reference to the image attribute work in MMUSIC. If I understand the above
correctly it should be possible for the offerer to specify a parameter set that
says 352x288 resolution while the answerer can give a parameter set that says 400x300
as long as it is supported by the profile level id. Is this correct.

What 3GPP SA4 discussed on
this new SDP attribute, based on the feedback from IETF ’72, might complement
the answer by Mr. Roni Even.

(1) If
the answerer selects an image size from "a=imageattr", which
is the one in codec parameter set, such as

config
or sprop-parameter-set, then the sender can start media transmission
immediately.

(2) If
the answerer selects an image size, which is not the one in codec parameter
set, then the sender

sends
new codec parameter set. The method to send new codec parameter set or
acknowledge the reception

of the
new codec parameter set might depend on the codec selected.

The
discussion covered also the following topics.

- It is
considered that not specifying image size information in the
sprop-parameter-set, as suggested

in the
clause 5 of the Internet draft, is not alowed.

- In
case of H.264, multiple codec parameter sets can be combined and put in a
sprop-parameter-set.

Please understand that
although it is SA4 that requested MMUSIC to define “a=imageattr,” SA4 will use
only a subset of its capability set.

We are not sure whether asymmetric setup
or change of resolution during a session would be allowed for 3GPP mobile
terminals, but we

recognize such necessities if “a=imageattr” is to be used by a
wide set of applications. We will be happy to share some examples we faced

in
circuit-switched video telephony, 3G-324M.

In clause 6.6 of 3GPP
TS 26.111, two paragraphs deal with change of codec parameters.

If the
operational mode of MPEG-4 Visual encoder needs to be changed, the existing
MPEG-4 video logical channel shall be closed and

H.245 [6] procedures for
opening a new MPEG-4 video logical channel shall be started. The new
operational mode shall be indicated in the

parameters of the new logical
channel.

If H.264
picture parameter sets need to be changed or new sets need to be added during a
session, it may be done either by opening a new

logical channel using the same
procedure as described above or within the current channel, by including
picture parameter set NAL units

directly in the bitstream.

In case of MPEG-4, 3GPP
requires closing current logical channel (a concept close to session) and
opening a new one while for H.264,

change of codec parameters on the fly is
allowed. This might be due to the differences in the structure of two codecs.

For change of resolution using
“a=imageattr” during a session, probably sending a SDP offer, there will be
more issues to consider.

Whether the SDP offer contains change of bit-rate or
not, action of the sender will be quite different. Especially in the latter
case, the problem

will be more complicated.

Suppose that a sender
received a request to increase the resolution from 224x176 to QVGA, at the same
bit-rate. Then the sender increase

the resolution, by configuring camera and
codec, but the sender has the freedom to achieve this by either reducing frame
rate while avoiding

quality loss, or reducing image quality while avoiding the
reduction of frame rate. In fact, both frame rate and image quality can be
reduced.

This is somewhat related to
the spatiotemporal tradeoff using videoTemporalSpatialTradeoff in H.245 or “a=quality.”
As we explained

previously, neither works satisfactorily since there is no way
to clearly map the value, 0-31 or 0-10 that accompanies either message, to

actual
codec operation.

If change of resolution
during a session is intended, then the above issues should be clarified.

Best regards,

Kyunghun Jung

Samsung Electronics

------- Original Message -------
Sender : Roni Even<[email-masked]>
Date : 2008-09-09 19:39 (GMT+09:00)
Title : RE: [AVT] SDP Negotiation based on Profile-Level-Id

YK,

This is the new mode request in H.241 and I think that maybe Tom should look

at how to address it.

Roni

-----Original Message-----

From: [email-masked] [mailto:[email-masked]]

Sent: Tuesday, September 09, 2008 1:28 PM

To: [email-masked]; [email-masked]

Cc: [email-masked]; [email-masked];

[email-masked]

Subject: RE: [AVT] SDP Negotiation based on Profile-Level-Id

Roni,

OK, so you want spatial resolution to be changeable during a session. One

think I don't know is that, in the use case you mentioned, how does the MCU

request a lower resolution from the receiver?

BR, YK

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