athomason/xmms-syncup

xmms-syncup allows instances of the XMMS media player running on one or more client machines to play synchronously with a designated server player

xmms-syncup is a C language plugin to the XMMS media player that provides
real-time synchronization of audio playback.  This is useful in environments
such as dorms, houses, or work environments where multiple networked computers
have independently driven speakers.  

xmms-syncup works by periodically querying the server as to which file it is
playing, and how far it is into it (XMMS provides millisecond resolution for
the playback cursor, though in practice this is reliable only to 10ms,
depending on the sound system in use).  xmms-syncup uses heuristic algorithms
to set the local player's cursor to match the server's as closely as possible.
This is obviously dependent on the ping times between the machines; however, we
can reasonable assume that machines whose speakers are close enough to be heard
by one listener will have short ping times (our 100baseT ethernet has sub-1ms
ping, more than sufficient).

Since queries to the server are frequent, clients recover quickly from song
changes or manual seeking on the server.  Any clock skew (noticed e.g. when
using ALSA and OSS on different machines) is also corrected for inherently.

xmms-syncup is not a streaming server and does not provide for file sharing:
file paths in the server's playlist must be valid on all hosts.  We have found
NFS to be an acceptable solution for file distribution.  Alternatives (Samba,
AFS) would likely work as well.  The playlist itself is shared, however: if the
client detects that its playlist differs from the server's, it clears the local
list and requests a copy from the server.  In practice, this means that changes
made in the server's player are propogated quickly to the clients.

xmms-syncup has achieved acceptable stability and performance for our small
workgroup.  We primarily are interested in using SourceForge's hosting and bug
tracking facilities for xmms-syncup.  Since Future development will likely be
limited to tuning parameters and increasing configurability through the GTK
GUI.


Heritage: xmms-syncup is based on the GPL'ed xmms-netamp plugin which slaves
XMMS clients to a Winamp server.
http://axelbrown.com/xmms/xmms-netamp-0.2.1.tar.gz

Requirements: 1) the server must be running the GPL'ed xmmsd plugin
(http://xmmsd.sourceforge.net) to provide state information about its player to
clients.  If there is demand, a drop-in replacement server for xmmsd may be
written to provide the necessary features for xmms-syncup.  2) Synchronization
is greatly improved by running NTP or equivalent to maintain consistent system
clocks.

Portability: xmms-syncup has no more compilation dependencies than xmms itself.
These are primarily glib and gtk.  xmms-syncup has been developed and tested on
the Gentoo/x86 and FC3/amd64 Linux platforms.

Pitfalls of alternate solutions:

1) Manual solutions (hitting "play" on the count of 3) are inconvenient and
error-prone

2) Streaming solutions attempt to minimize gaps in playback, and so use
variable client buffers that are not synchronized between clients

3) Hardware solutions (such as the SqueezeBox) require additional investment 

4) The most mature software solution for *NIX is the SlimServer, which requires
a custom player and has poor configuration options for synchronization

In contract, xmms-syncup is lightweight, robust, and compatible with one of the
most popular media players for Linux.