Re: [AVT] imageattr and codec parameter sets (with embedded image size info)

[Randell Jesup <rjesup at wgate.com>]

Kyunghun Jung <kyunghun.jung at samsung.com> writes:
>Then we might also need to comment on MPEG-4's config, which does similar
>roles as sprop-parameter-sets of H.264.
>
>In addition, config includes image size information too. P. 38 of 3GPP TS
>26.234 says:
>
>
>
>The frame size field in SDP is needed by the client in order to properly
>allocate frame buffer memory.   For MPEG-4 Visual streams, the frame size
>shall be extracted from the "config" information in the SDP. For H.264
>(AVC) streams, the frame size shall be extracted from the
>sprop-parameters-sets information in the SDP. For H.263 streams, a PSS
>server shall include the "a=framesize" field at the media level for each
>stream in SDP, and a PSS client should interpret this field, if present.
>Clients should be ready to receive SDP descriptions without this
>attribute.

a=framesize is not defined (that I know of) for H.263, nor is it generic.
It appears to be specific to 3GPP and not defined by any IETF RFC or draft.
The paragraph above doesn't specify the interactions between a=framesize
and H.263 fmtp lines ("CIF=2", etc).  Does a=framesize override the fmtp
preferences?  Must the value in a=framesize be listed in the fmtp, and what
happens if it isn't, or is that invalid?

>We might need to check whether other bitstream of config or
>sprop-parameter-sets does not change after the size information is
>removed,

I don't think you can remove the size fields from parameter sets, but I'd
have to check the spec to be sure.

-- 
Randell Jesup, Worldgate (developers of the Ojo videophone), ex-Amiga OS team
rjesup at wgate.com
"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)

_______________________________________________
Audio/Video Transport Working Group
avt at ietf.org
https://www.ietf.org/mailman/listinfo/avt