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

[Spectr]

Hello.

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


-- 
With best regards, Spectr.
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