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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Hi Olle,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Maybe you missed Duane’s post
as the mailing lists switched around…<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> I can add that we often pass multi-packet
images through asterisk on a LAN with no problems. I think they’d have to
be in excess of 20 packet images and therefore more than 35kbytes… that’s
a big video frame. I think the fragmentation methods talked about by Duane
appear below Asterisk’s radar for RTP, Ast just sees the packetization as
payload. If your friend is seeing large frames lost then Ethereal has some
good(ish) support for H.263 – though there is a bug in the H.263 disector
that shows the timestamps as bad at the end of an image. <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Don’t forget about the packet
swapping issue I’ve raised before: we have a couple of customers that
have ISP connections that will switch packets around if packet n+1 is sent too
close to packet n and where packet n+1 is smaller than n (we usually see the
swap if packet n+1 is less than around 700 bytes on the wire). The packet swap
will show as lost frames in the target video system. Ethereal will show these
problems if captured on Ast box (do a Stats->RTP->ShowAllStreams and then
select the H.263 stream and analyze).<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Sequence numbers should
increment even with packets that are from the same video frame.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> Timestamps must stay the same for
each encoded image.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> I’m not sure what you mean
about the format drivers assuming a wrong size for two frames???<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>John<o:p></o:p></span></font></p>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span lang=EN-US
style='font-size:10.0pt;font-family:Tahoma;font-weight:bold'>From:</span></font></b><font
size=2 face=Tahoma><span lang=EN-US style='font-size:10.0pt;font-family:Tahoma'>
asterisk-video-bounces@lists.digium.com
[mailto:asterisk-video-bounces@lists.digium.com] <b><span style='font-weight:
bold'>On Behalf Of </span></b>Duane Storey<br>
<b><span style='font-weight:bold'>Sent:</span></b> 16 May 2006 22:24<br>
<b><span style='font-weight:bold'>To:</span></b> Discussion of video media
support in Asterisk<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [asterisk-video] How
do you send large frames?</span></font><span lang=EN-US><o:p></o:p></span></p>
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<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>Hi,<br>
<br>
Video frames are typically split into smaller chunks via fragmentation of the
video data itself. For example, H.263 has two packetization modes (RFC
2190 and RFC 2429). In these RFCs, it describes how you can split one
frame into multiple UDP packets. H.264 is a little nicer since it was
written with networks in mind -- each H.264 "chunk" is called a NAL
(network abstraction layer) unit. Encoders can output small NALs
directly and keep the packet less than MTU. <br>
<br>
Duane<o:p></o:p></span></font></p>
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<p class=MsoNormal><span class=gmailquote><font size=3 face="Times New Roman"><span
style='font-size:12.0pt'>On 5/16/06, <b><span style='font-weight:bold'>Olle E
Johansson</span></b> <<a href="mailto:oej@edvina.net">oej@edvina.net</a>>
wrote:</span></font></span><o:p></o:p></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>(retransmitting this for the mail archives)<br>
<br>
Friends,<br>
<br>
I am still a student in the video area... One question I have is how<br>
you send large video frames over UDP/RTP?<br>
UDP fragmentation? Or do you use the multiple RTP frame function - <br>
where you use the same seq number?<br>
Or any other trick?<br>
<br>
I got an error report from a friend that we somehow cancelled or cut<br>
large frame updates.<br>
<br>
Also, the format drivers for video seems to make an illegal <br>
assumption about the size of two frames.<br>
<br>
/O<br>
<br>
<br>
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