Subject: [AVT] change to draft-ietf-avt-rfc2429-bis-09.txt

From: "Even, Roni" <[email-masked]>
Date: Mon, 15 Jan 2007 15:18:14 +0200

Hi,
During the author48 we found out that the CPCF parameter is not well defined. What was missing is a way to specify a different maximum frame per second rate for each of the supported resolution.
The editors of the draft would like to have the following changes to this parameter as specified in the text below and looking for feedback if this sounds reasonable.
We would like to have this simple solution in order to be able to publish this draft.

Thanks
Roni Even

Section 8.1.1:

OLD

CPCF - Arbitrary (Custom) Picture Clock Frequency: CPCF is a
      floating point value.  Default value is 30/1.001 (approximately
      29.97) Hz. The floating point value indicates the nearest value
      given by the formula 1800000/(cd*cf) provided in the RTP Timestamp
      semantics in Section 3.1 above (as specified in H.263 section
      5.1.7).  For example, the value 29.97 indicates the picture clock
      frequency 1800000/(60*1001) = 30/1.001 Hz (for which cd is equal
      to 60 and cf is equal to 1001).

NEW

CPCF - Arbitrary (Custom) Picture Clock Frequency: CPCF is a comma-
      separated list of eight parameters specifying a custom picture
      clock frequency and the MPI (minimum picture interval) for the
      supported picture sizes when using that picture clock frequency.
      The first two parameters are cd, which is an integer from 1 to
      127, and cf, which is either 1000 or 1001.  The custom picture
      clock frequency is given by the formula 1800000/(cd*cf) provided
      in the RTP Timestamp semantics in Section 3.1 above (as specified
      in H.263 section 5.1.7). Following the values of cd and cf, the
      remaining six parameters are SQCIFMPI, QCIFMPI, CIFMPI, CIF4MPI,
      CIF16MPI, and CUSTOMMPI, which each specify an integer MPI
      (minimum picture interval) for the standard picture sizes SQCIF,
      QCIF, CIF, CIF4, CIF16, and CUSTOM, respectively, as described
      above.  The MPI value indicates a maximum frame rate of
      1800000/(cd*cf*MPI) frames per second for MPI parameters having
      a value in the range from 1 to 2048, inclusive. An MPI value
      of 0 specifies that the associated picture size is not supported
      for the custom picture clock frequency.  If the CUSTOMMPI
      parameter is not equal to 0, the CUSTOM parameter SHALL also be
      present (so that the Xmax and Ymax dimensions of the custom
      picture size are defined).

Section 8.2.1

OLD

   Below is an example of H.263 SDP in an offer:

      a=fmtp:xx CIF=4;QCIF=2;F=1;K=1

   This means that the sender of this message can decode an H.263 bit
   stream with the following options and parameters: preferred
   resolution is CIF (its MPI is 4), but if that is not possible then
   QCIF size is O.K.  Advanced Prediction mode (AP) and slicesInOrder-
   NonRect options MAY be used.

NEW

   Below is an example of H.263 SDP in an offer:

      a=fmtp:xx CIF=4;QCIF=2;F=1;K=1

   This means that the sender of this message can decode an H.263 bit
   stream with the following options and parameters: preferred
   resolution is CIF (at up to 30/4.004 frames per second), but if
   that is not possible then QCIF size is also supported (at up to
   15/1.001 frames per second). Advanced Prediction mode (AP) and
   slicesInOrder-NonRect options MAY be used.

   Below is an example of H.263 SDP in an offer that includes the
   CPCF parameter.

      a=fmtp:xx CPCF=36,1000,0,1,1,0,0,0,2;CUSTOM=640,480,2;CIF=1;QCIF=1

   This means that the sender of this message can decode an H.263 bit
   stream with a preferred custom picture size of 640x480 at a
   maximum frame rate of 25 frames per second using a custom picture
   clock frequency of 50 Hz. If that is not possible, then the 640x480
   picture size is also supported at up to 15/1.001 frames per second
   using the ordinary picture clock frequency of 30/1.001 Hz.  If
   neither of those is possible, then the CIF and QCIF picture sizes
   are also supported at up to 30/1.001 frames per second using the
   ordinary picture clock frequency of 30/1.001 Hz.

END

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

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From: Randell Jesup <[email-masked]>
Date: Tue, 16 Jan 2007 21:01:25 -0500

>   slicesInOrder-NonRect options MAY be used.

For QCIF, wouldn't that be "30/2.002" not "15/1.001"?  Yes, I know
the math works out the same, but saying it as 15/1.001 will confuse
people.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
[email-masked]
"The fetters imposed on liberty at home have ever been forged out of the weapons
provided for defence against real, pretended, or imaginary dangers from abroad."
		- James Madison, 4th US president (1751-1836)

---

From: Colin Perkins <[email-masked]>
Date: Thu, 18 Jan 2007 12:00:48 +0000

> the math works out the same, but saying it as 15/1.001 will confuse

That seems a reasonable change, and the authors have (privately)  
agreed that it makes sense. Since there were no other comments, we'll  
make that change, and get this to the RFC Editor now.

-- 
Colin Perkins
http://csperkins.org/