Subject: [AVT] Maximum non-scaled image size

From: Henning Schulzrinne <[email-masked]>
Date: Sun, 19 Dec 2004 19:52:16 -0500

Do any video payload formats specify, as SDP format attributes or 
otherwise, the maximum image size supported natively (i.e., without 
downscaling)?

For a draft we're working on, I'd like to re-use any existing 
conventions. In general, it would seem useful to know this since there 
isn't much point in sending at a higher resolution than the screen 
resolution or the maximum size that an application can handle. This 
seems like a natural extension to a=framerate in SDP.

Henning

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---

From: "Gary Sullivan" <[email-masked]>
Date: Sun, 19 Dec 2004 17:32:01 -0800

There are ways to declare an image size as part of a decoder capability
or a decoder preference indication in both H.245 and SDP (and perhaps
other places too, most likely including H.241 and what H.320 uses) -- I
would suggest checking the design in regards to H.263 as that has
probably been the most commonly used video codec in two-way
communication scenarios.

When specified as part of a declaration of decoder capability, an image
size would ordinarily be interpreted as the maximum that the decoder
could decode, rather than as the maximum it can display.  But if
specified as a decoder preference, its interpretation would be more akin
to what you mention.  That would be a declaration of what image size the
decoder would most like to receive, although perhaps not necessarily an
indication of exactly why.  In some sense, that might be a better thing
to design than what you seek.  (Why pick only one specific reason for
the decoder to indicate its preference for something?)

A decoder might also, of course, use censorship of its decoder
capability declaration to simply not declare capabilities beyond its
native display resolutions.

>From draft-ietf-avt-rfc2429-bis-03.txt (September 2004, section 8.1),
there is a way in SDP for an H.263 decoder to indicate an ordered list
of preferences for picture resolution and frame rate.  (That stuff is
also probably in the original RFC 2429 as well -- I just happen to have
checked the "bis" draft).

Best Regards,

Gary Sullivan

+> -----Original Message-----
+> From: [email-masked] [mailto:[email-masked]] On 
+> Behalf Of Henning Schulzrinne
+> Sent: Sunday, December 19, 2004 4:52 PM
+> To: [email-masked]; [email-masked]
+> Subject: [AVT] Maximum non-scaled image size
+> 
+> Do any video payload formats specify, as SDP format attributes or 
+> otherwise, the maximum image size supported natively (i.e., without 
+> downscaling)?
+> 
+> For a draft we're working on, I'd like to re-use any existing 
+> conventions. In general, it would seem useful to know this 
+> since there 
+> isn't much point in sending at a higher resolution than the screen 
+> resolution or the maximum size that an application can handle. This 
+> seems like a natural extension to a=framerate in SDP.
+> 
+> Henning
+> 
+> 
+> _______________________________________________
+> Audio/Video Transport Working Group
+> [email-masked]
+> https://www1.ietf.org/mailman/listinfo/avt
+>

---

From: "Even, Roni" <[email-masked]>
Date: Mon, 20 Dec 2004 09:32:21 +0200

Henning,
In the bis drafts for the H.263 and H.261 I added the support for
specifying the image size that the decoder can receive per frame rate.
For H.261 the support is for fixed resolutions for H.263 the support is
also for custom formats. See draft-ietf-avt-rfc2429-bis-03.txt and
draft-ietf-avt-rfc2032-bis-03.txt
In the H.264, see draft-ietf-avt-rtp-h264-11, the concept was that the
decoder, using the level parameter, specifies the number of macro blocks
per second it can process; The level as specified in H.264 gives a
maximum on the frame rate and resolution. The level parameters can be
overridden by the optional parameters specified in the draft.

The transformation from the decoder to the display is up to the
implementer.  

As can be seen in H.261 and H.263 the SDP from the receiver can specify
an exact picture size(resolution)it can receive, but still the encoder
can send any allowed picture size that is bellow the decoder capability.
For example in H.261 if the decoder specifies it can receive a CIF
picture at 30 fps, the encoder can send a QCIF picture at 15 fps. 
In H.264 there is no explicit resolution specified.

Roni Even

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf
Of Henning Schulzrinne
Sent: Monday, December 20, 2004 2:52 AM
To: [email-masked]; [email-masked]
Subject: [MMUSIC] Maximum non-scaled image size

Henning

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