Subject: [AVT] comments on draft-kristensen-avt-rtp-h241param-01

From: "Charles Eckel (eckelcu)" <[email-masked]>
Date: Sun, 7 Nov 2010 19:24:21 -0800

Hi Tom,

Thanks for putting this together. It is very well written and I agree it
is important.
I have some minor comments to share:

1) It would be good to state the expanded form of max-fps before the
first time you use it in the text. This would be especially insightful
for those familiar with RFC 3984-bis but not familiar with H.241

2) Where you state:

   The new parameter MaxFPS is introduced in H.241 - Amendment 2 to
   remove this issue, by constraining the allowed parameter range for
   systems supporting this extension.  This draft proposes adding the
   optional parameter max-fps for use in SDP-based signalling.

I believe you mean constraining the maximum frame rate, only. There is
no minimum frame rate.

3)   It is worth emphasizing that systems that does [cue s/does/do] not
support and
   understand the max-fps parameter are free to produce streams as
   before, within the bounds specified by the existing parameters.

4)  You write:

      Editorial note: To be decided whether the stream property (sender
      capability) usage of max-fps is useful for SDP usage, i.e. with
      sendonly and for declarative usage.

I do not see a need for max-fps as stream property, but I am ok with
adding it if doing so makes it align better with existing media
properties.

5. You write:

   The "a=framerate" limitation allows a global maximum frame rate to be
   specified for the video media, this limit applies to all codecs in
   the video media section.  In cases where both "a=framerate" and codec
   specific limits are specified, the maximum frame rate that can be
   used for a codec is the minimum of the values specified globally and
   specifically for a codec.

This is required only if framerate is bi-directionally binding.
Otherwise, if there is a codec for which no codec specific mechanism
exists and for which I can receive only 30 fps, but for H.264 I can
receive 60 fps, I would like to be able to specify framerate=30,
max-fps=60 and have result in receiving up to 60 fps for H.264.

Cheers,
Charles