CMPlayer

Wed May 12 19:01:51 DST 2004

Software:

CMplayer is a patch for MPlayer which lets you synchronise several players running on several computers (hence the name, Cluster MPlayer; but I may change it in the future) connected to a dedicated LAN.

So, every host will load a movie from its internal storage media, and all of them will be played at the same speed, i.e., all of them will start at the same moment and after some time, all of them will have played the same number of frames at a fixed framerate.

Applications could be:

• CAVE
• Videowall

Requeriments:

• All of the movies will have the same framerate.
• The movies will have no sound track. By now, I don't need sound, so I have not coded anything for sound tracks synchronisation. Sorry...

How it works:

First, you need to get the system clocks of all of your computers synchronised. I'd sugest to use NTP for this purpose.

According to my experiments, using NTP, gettimeofday() returns differences below 40 ms; which is good enough for the usual 25 fps movies:

    # sec:usec = 1069231417:653136
    # sec:usec = 1069231417:653433
    # sec:usec = 1069231417:656074
    # sec:usec = 1069231417:653073
    # sec:usec = 1069231417:653663
    # sec:usec = 1069231417:653664

Then, you need a modified mplayer which can:

• Start playing at some exact time; and this "start time" will be received at the same instant in all of the computers.
• Synchronise the reproduction to internal system clock.

So, in short, cmplayer project patches mplayer so it will be able to behave this way.

The cmplayer session:

We will use a computer as "master". This computer will take care of

• Act as master for NTP time synchronisation.
• Start mplayer on every "slave" computer.
• Check if all of them started properly.
• Send the "start" command to every "slave".

    master                          slave1  slave2   ...  slaveN

    runs "cmplayers"

    runs remote mplayer --- rsh --> mplayer1    mplayer2    mplayerN

        |                               |           |           |
        v

    [cmplayers waits]  <-- ["ready" tcp/ip packet ]
        |              <----------------------- ["ready" tcp/ip packet ]
        |              <------------- ["ready" tcp/ip packet ]
        |                               |           |           |
    we have N answers                   |           |           |
    so cmplayers exits                [wait]      [wait]      [wait]
        |                               .           .           .
    runs cmplayerc                      .           .           .
        |                               .           .           .
        ---[ "start" TCP/UDP bcast ] -->----------->----------->
                                        |           |           |
                                <------             |           |
    [ OK || "Too Late" answer ] <-------------------            |
                                <-------------------------------
        |                               |           |           |

    cmplayerc exits                   [play]      [play]      [play]

• cmplayer source code

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  See also:

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  e-mail:

  • spd@daphne.cps.unizar.es

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