RE: [AVT] Interop issue with H263-1998

[Gary Sullivan <garysull at windows.microsoft.com>]

I don't think I have seen a direct reply to this message.  Here is my attempt to answer Guido's question:

RFC 2429 did not have any SDP specification in it (in fact the string "SDP" is not found in RFC 2429).

It is true that RFC 2429 defined an RTP payload packetization scheme that was capable of carrying H.263 data either with or without the various optional H.263 features.  However, in practice, RFC 2429 depended on some externally-defined method (not specified in the RFC) of figuring out which such features would be used in the bitstream.  One such externally-defined method was/is H.245, which supports some pretty elaborate capability declaration expressions for such feature capability negotiation.  But the SDP definition found in RFC 4629 is for scenarios that do not use such an H.245 capability exchange protocol.  I don't actually know where the SDP definition for H.263 was specified before RFC 4629 existed.  However, I am sure that it was not OK to send a fancy combination of obscure H.263 optional features in a bitstream using SDP before RFC 4629.  My understanding is that the majority of H.263 usage is still the "baseline" (no optional modes) configuration, and that is really all that anyone can assume is found in an implementation unless they have some way of knowing otherwise.

As far as I know, someone can hypothetically still use H.263 with H.245 (without using SDP), and such use would be considered in conformance with RFC 4629, regardless of which optional modes were being used.  I believe that the wording "current implementations will not send any optional parameters in their SDP..." in RFC 4629 only applies to when SDP is being used.

Best Regards,

Gary Sullivan


+> -----Original Message-----
+> From: Franceschini Guido
+> [mailto:guido.franceschini at telecomitalia.it]
+> Sent: Tuesday, August 21, 2007 8:49 AM
+> To: avt at ietf.org
+> Cc: Paltro Pier Carlo
+> Subject: [AVT] Interop issue with H263-1998
+>
+> Dear all,
+>
+> I have an issue with the definition of the H263-1998 media type.
+> In the RFC 2429, no optional parameters are defined,
+> implying that any valid H263+ stream could be streamed.
+> In the RFC 4629, that obsoletes 2429, various optional
+> parameters are specified, which allow specifying the
+> (decoder) support to the various annexes.
+>
+> What confuses me is the following statement in RFC 4629,
+> concerning H263-1998
+>
+>    Interoperability considerations:
+>
+>       These are receiver options; current implementations
+> will not send
+>       any optional parameters in their SDP.  They will ignore the
+>       optional parameters and will *** encode the H.263
+> stream without any ***
+>       of the annexes.  Most decoders support at least QCIF
+> and CIF fixed
+>       resolutions, and they are expected to be available
+> almost in every
+>       H.263-based video application.
+>
+> Indeed my understanding would be quite different, and I
+> would have written instead:
+>
+>       These are receiver options; current implementations
+> will not send
+>       any optional parameters in their SDP.  They will ignore the
+>       optional parameters and will *** encode the H.263+
+> stream with possibly all ***
+>       of the annexes.  Most decoders support at least QCIF
+> and CIF fixed
+>       resolutions, and they are expected to be available
+> almost in every
+>       H.263-based video application.
+>
+>
+> Any clarification would be welcomed
+>
+> Best regards
+> Guido Franceschini
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