[vlc-devel] Re: New Patch for RTSP offset feature.

[Marian Durkovic]

On Wed, Oct 11, 2006 at 07:53:19AM +1000, Rob Casey wrote:
> > Talking about Amino - well, proper support of standars has 
> > never been the case with them. When one of our local service 
> > providers tried to convince them to support TS in RTP (since 
> > TS in raw UDP is utterly flawed in principles), they simply 
> > didn't care any bit.
> 
> The thing is that it's not just Amino at fault here. I've seen the same
> with a number of IPTV STB manufacturers and unsurprisingly invariably it
> comes down to the numbers where developing a client around raw UDP
> rather than RTP is more acceptable in implementation and maintenance
> cost.

Rob,

   since I'm one of the authors of RTP reordering code for VLC, I really
don't understand what extra costs could be involved. I'm not speaking
about separate audio/video streams delivered over multiple RTP streams,
which require RTCP synchronization etc. I'm just saying that the TS 
payload should not be placed directly into UDP packets but a 14-bytes 
RTP header needs to be added in between. This RTP header contains sequence
number, which _must_ be used by the client to restore correct order of
packets and drop duplicates. 

   The current STB implementations seem to believe that IP multicast will 
deliver packets in correct order and only once. While this naive approach
might work in a very limited environment, once you add some redundancy to
the network and/or high-speed interfaces, it immediately fails.

   Working implementation of RTP reordering for client side is part of VLC
for almost 1 year now:

https://trac.videolan.org/vlc/log/trunk/modules/access/udp.c

   I'm quite surprised that the STB manufacturers refuse to implement this.
Maybe they need to found out the hard way - when one of their major
customers upgrades his networks and suddenly all IPTV streams break.



	With kind regards, 
     
  		M.

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----   Marian Durkovic                       network  manager         ----
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