[streaming] Re: Reliable streaming format for wireless links

[Romuald CARI]

Niall Donegan a écrit :

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>I'm setting up a server to stream the input from a Hauppauge PVR-150
>card and it works very nicely here over the wired network. The command
>I've using for vlc is:
>
>vlc pvr:/dev/video0:norm=pal:size=720x576 -I telnet --sout udp:239.0.0.1
>- --ttl 1
>
>which pipes the mpeg2 output straight over vlc.
>
>The problem is that when I start to use a wireless link (2x Linksys
>WAP54G in bridge mode) there is random errors showing up in the video
>stream.
>
>I know the problem is that udp doesn't garrentee packets will get there
>which hasn't been a problem on the wired network, but what method or
>protocol would be more appropriate for multicasting over wireless?
>
>Thanks.
>
>
>- --
>Niall Donegan
>niall\at\moybella\dot\net
>Public-Key: http://moybella.net/~niall/public.gpg
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>  
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UDP + Wireless create creepy things.
The problem is that in UDP broadcast / multicast, packets are send once 
for all with no transmission check. Wireless protocols can not guarantee 
that all UDP datagrams will be transmitted properly. The only way to get 
a "secure" transmission over wireless links, I think, is to establish a 
TCP connection, using HTTP protocol for example, and to set a huge 
buffer time on the client side (10 seconds maybe). The HTTP protocol, 
because it uses TCP will handle the errors and resend the data as much 
as necessary, so you should not see those creepy things in your image. 
You can not create "secure" multicasting over wireless networks, there 
is no way to guarantee that yout clients will get all the data.

You could try to reduce the stream bandwidth and create unicast TCP 
connections to your clients using HTTP, good luck !

Romuald

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