[vlc] Re: H263 over RTP

[chris.2.dobbs at bt.com]

Hi Ross,
Thanks again for info. I did use your code to stream h263 but I wanted
to understand how it was done and as I like the pain that was what I
did. Finally got it working and in the process discovered something you
may be interested in.

During my exploits with ethereal to check my packets againsed the
reference model live555 packets, I think I 'may' have found a tiny
little bug in your code - or I have simple misunderstood something.

To discern between overflow packets i.e packets that are part of a frame
spanning several packets, we look for the occurance of '0000' in the
bitstream, these 2 bytes are then discarded. This all works fine and
dandy in your code but NOT when it comes across a sequence of '000000'
i.e 3 bytes of zeros, the 3rd zero seems to have been added to the end
of the current packet instead of (I think) prefixed to the beginning of
the next packet.

So, for example, say the bitstream snapshot looks like this is:
....Ad 13 22 b1 00 00 00 12 22 11...

The current packet should have ended with "ad 13 b1"
The next packet (pbit set to 1) should start with "04 00 00 12 22 11"
(04 00 being the h263 header as I'm sure u know!)

Your code seems to show this however:
Current packet ending with "ad 13 b1 00"  - the spurious '00' being
taken as part of this frame
Next packet starting with "04 00 12 22 11"
Thus a zero data byte has been placed in the wrong reference frame.


No big deal I know but VLC does throw a few errors when I play your
stream so maby this is it?

The packet I noticed this on as a start of frame packet (pbit=1 and had
an eof frame marker.
Hope this is useful for you and thanks again or a great product.
Regards,
-Chris

-----Original Message-----
From: vlc-bounce at videolan.org [mailto:vlc-bounce at videolan.org] On Behalf
Of Ross Finlayson
Sent: 08 March 2007 05:08
To: vlc at videolan.org
Subject: [vlc] Re: H263 over RTP

>Hi, Chris
>      There are three RFCs about h.263 packet, that is RFC 2190,
>RFC2429 and RFC4629. Doe vlc support all these three RFCs?

VLC supports the RFC 2429 and RFC 4629 payload formats (which are
essentially the same; the only difference being that RFC 4629 defines
some additional optional parameters).  More precisely, VLC supports the
"video/H263-1998" and "video/H263-2000" MIME types.

Note that the RFC 2190 format is now obsolete, and no new
implementations of H.263 RTP streaming should be using it.

(By the way, the "LIVE555 Streaming Media" software implements the
*transmission* of H.263 RTP streams, as well as reception.  if all these
people recently who have been trying to build H.263 streamers had just
used the LIVE555 software, they would haved saved themselves lots of
flailing around...)
-- 

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

--
This is the vlc mailing-list, see http://www.videolan.org/vlc/ To
unsubscribe, please read http://www.videolan.org/support/lists.html

-- 
This is the vlc mailing-list, see http://www.videolan.org/vlc/
To unsubscribe, please read http://www.videolan.org/support/lists.html