[vlc-devel] Synchronisation between players for network streams.
gbazin at altern.org
Thu May 27 14:34:02 CEST 2004
I just added a new module called "netsync" which allows several players to
be kept synchronised (relatively precisely) when playing the same network
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
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
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
Anyway, just wanted to share the few thoughts I had on this.
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