[vlc-devel] Re: Synchronisation between players for network streams.

hornsby adrian_hornsby at yahoo.co.uk
Thu May 27 14:46:50 CEST 2004


do you think it could be possible to synchronise 3 players together with 3 
different streams but from VLS ? what would be needed in your module for 
that ??

On Thursday 27 May 2004 15:34, Gildas Bazin wrote:
> Hi all,
> I just added a new module called "netsync" which allows several players to
> be kept synchronised (relatively precisely) when playing the same network
> stream.
> The original aim of this module is to avoid an echo effect when you have
> several VLC players which are playing the same stream in the same room.
> I'm not actually sure that this module is that helpful because VLC already
> keeps a very good synchronisation with the server that is sending the
> stream (at least in case of MPEG TS). But theoretically this
> synchronisation is not precise enough because it can vary by a small fixed
> delay (because of some caching on the network stack of the hardware or OS
> or even induced by VLC itself). So basically I wanted to experiment a bit
> with this.
> This module is still quite basic so right now you have to start a "master"
> VLC player (which will be used as the reference clock) like this:
> "vlc --extraintf netsync --netsync-master udp://@blabla"
> Then start the "slave" clients with:
> "vlc --extraintf netsync --netsync-master-ip=yourmasterip udp://@blabla"
> In the few tests I've done, I haven't really noticed any improvements in
> the synchronisation when doing udp multicast streaming (ie. the
> synchronisation was already really good without netsync). But admittedly,
> high bitrate streams (video+audio) shouldn't really be affected by caching
> issues in the OS/hardware. There seems to be a small gain however when
> running low bitrate audio only streams.
> Netsync has the advantage though of harmonising the caching parameters of
> all the VLC players on the master's one. So for instance if all the players
> don't have the same caching value (--udp-caching/--http-caching) this won't
> matter.
> The other big advantage is for http streaming (with VLC). HTTP streaming
> doesn't maintain a very good synchronisation between all the clients
> (because it is using PULL streaming). So here netsync is actually very
> useful.
> Anyway, just wanted to share the few thoughts I had on this.
> --
> Gildas

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