[vlc-devel] receiving HVDTS MPEG2 strams: UDP makes artifacts, RTP is OK.

[Rémi Denis-Courmont]

Le lundi 14 décembre 2009 19:01:42 Claudio Allocchio, vous avez écrit :
> >  this is most probably due to packet reordering happening somewhere on
> > the path between the server and you. 10G interfaces on Juniper M160
> > routers are famous for this.
> 
> it is true that there are plenty of M160 and 10G interfaces between
> Internet2 and GEANT and GARR... but we have the same result over a pure
> LAN connection, too.
> 
> It might be related to the amount of packets, of course, as 28Mbps can
> cause packets reordering also in switches.
> 
> However, when we use just DVTS to DVTS (DVTS also as receiver) we run UDP
> at 30Mbps, and we never have a single video glitch for hours.

There are a few potential differences though.

First, VLC does _not_ attempt to correct packet ordering based on the 
continuity counter. Instead, it assumes a discontinuity means a packet loss, 
which in most cases: file storage, DVB reception, simple IP networks. I don't 
know how DVTS handles this.

Second, VLC tries to set rather large socket receive buffers. However most 
operating systems will pad the limit to a much lower value for security 
reasons. Hence, at outragous rate, buffer overflow and then packet loss is 
likely to occur (Windows seems more prone to this than Linux, but this is 
entirely empirical).

-- 
Rémi Denis-Courmont
http://www.remlab.net/
http://fi.linkedin.com/in/remidenis