Re: [clue] Incoming liaison statement from MPEG
Stephan Wenger <stewe <at> stewe.org>
2012-06-01 17:17:50 GMT
The statement was sitting in my inbox for a few days, and I have forwarded it to the secretariat for posting only this morning. Therefore, it is not yet on the tracker, but should be on the tracker sometime soon.
Color primaries, as one example, can actually being sent in SDP today, as part of the VUI in the sequence parameter set of H.264. And, color primaries are an interoperability point, at least for high quality applications (such as video contribution).
If your receiving box does not understand, or cannot meaningfully process color primaries as sent, then you may get a picture but it will look odd… There is also other stuff in the MPEG doc that is even more needed for interoperability; for example, association
of audio channels inside the codec bitstream with a speaker location.
The key point of the MPEG doc is that they are out farming generic codec things from the audio/video specs into this MPEG-A format, and we (as we are not using MPEG-A) will probably have to find a way to either encapsulate MPEG-A XML for cap exchange,
or translate the code points to SDP-ish things.
/* Font Definitions */
panose-1:2 4 5 3 5 4 6 3 2 4;}
panose-1:2 15 5 2 2 2 4 3 2 4;}
panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
font-family:"Times New Roman","serif";}
<at> page WordSection1
margin:1.0in 1.25in 1.0in 1.25in;}
I did not see the liaison statement yet in MMUSIC, so I hope it will be available in time for us to review.
From the example of color primaries I am not sure why we need to have this in SDP. if this is something that is sent as part of the payload do we
need to send it also in SDP?
MPEG is working towards codec independent code points, and has sent to MMUSIC a liaison statement asking for our input. Especially the audio stuff may also
be relevant to CLUE, so I copy CLUE here as well. No deadline is provided, but I note that MPEG meets two weeks before the Vancouver IETF meeting and the text they sent us is already a CD, so our time to influence their decisions (if we choose to do so) is
MPEG has observed that many code points relevant for audio and video are generic in the sense that they can be applicable to many video or audio codecs. Recent
MPEG (and joint MPEG/ITU) video coding standards have occasionally copy-pasted whole sections of code points concerning things like color primaries. They want to avoid this in the future. So they farm out stuff that is historically located in video/audio
codec specs, but are likely to be common between different codecs.
My hunch is that the code point in their draft standard could be translated to SDP-ish syntax. At this point, it is XML-ish.
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