[Live-devel] question about fmtp fields for MJPEG RTP

[Ross Finlayson]

>I work in Elphel, Inc 
>(<http://www3.elphel.com/index.php>http://www3.elphel.com/index.php), 
>we make high resolution network videocamera, what send videostream 
>over RTP/RTSP in MJPEG and Theora format.

I assume you're familiar with our Elphel server application code: 
http://www.live555.com/Elphel/

>I have question, about dynamic payload type for MJPEG in live555 library.
>
>RTP MJPEG RFC format with payload #26 have limitation for image size 
>- each size of image must be less than 2040 pixels, and larger size 
>not supported. In current live555 code exist hack for this 
>limitation - if width or height in MJPEG header == 0 - used 2048 
>size (what in general not correct, but ok for 3MPx sensors with 
>2048x1536 image). We start use 5MPx sensors, and get again this 
>problem.
>In SDP parser (of live555 library) exist parser of field 
>"a=x-dimensions:WW,HH", but this data used only for container - not 
>when we restore JPEG headers from MJPEG packets; and also, in code, 
>in this time we can't get access to this properties 
>(MediaSubsession::videoWidth(), MediaSubsession::videoHeight() ) of 
>subsession from JPEG packet implementation class.
>
>I ask about add support for this in live555 - use width and height 
>from subsession description, when we make JPEG headers from MJPEG 
>(JPEG images have limit to 65526 pixels, not in 2040, so all must be 
>ok with JPEG headers).
>
>And also, if this feature possible - may be, in live555 can be used 
>for image size not only this extension ("a=x-dimensions:..."), but 
>attributes from SDP "a=fmtp: width=WW; height=HH" attributes, like 
>in drafts of RTP Theora, or RTP JPEG2000? In general, it's easy, if 
>we can get access to subsession description from JPEG header class.

I'm generally reluctant to support attributes (like "x-dimensions") 
or payload formats that are not official IETF standards, or on the 
standards track.

It wasn't clear (to me) from your message exactly what it is that you 
are asking for.  Are you asking it/when we will support the JPEG 2000 
RTP payload format 
<http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-jpeg2000-12.txt>? 
Or are you asking that we support a non-standard SDP attribute with 
the RFC 2435 MJPEG RTP Payload Format?  (If it's the latter, then I 
would be very reluctant to do this.)
-- 

Ross Finlayson
Live Networks, Inc.
http://www.live555.com/
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