[mythtv-users] Basic concepts question

Joseph A. Caputo jcaputo1 at comcast.net
Tue Jan 20 09:55:06 EST 2004

On Monday 19 January 2004 22:37, stan wrote:
> On Mon, Jan 19, 2004 at 09:10:57PM -0500, J. Donavan Stanley wrote:
> > stan wrote:
> > >Can anyomne point to some docs, or provide me with help in
> > > understanding what functions are done by what peices of MythTV?
> > >
> > >What is done by a "master backend"/ What is done by a non master
> > > backend?
> >
> > A master backend controls one or more slave backends.
> OK, so what does the master backend do that the slave's don't do?

The master backend controls the scheduler.  Slave backends are 'dumb'; 
they just record what the master tells them to record.  Each backend 
records to its own locally-mounted directory (though that directory can 
be an NFS mount if you want all your video storage in one place, and 
have the bandwidth).

> What if I don't ave suficent backend CPU to decompress the files, and
> do the other things it needs to do> Or I don't have suficent network
> badnwith to stream over? BTW how much _is_ that?

Your frontend needs enough CPU to play back the files; a general rule of 
thumb is a bare minimum of 500MHz to play back a single stream.

Your network needs enough bandwidth to stream the file in real time.  
For MPEG-4 or MPEG-2 files, it's easy to calculate how much bandwidth 
you need from the bitrate of the recording.  For RTjpeg, it's not quite 
so cut-and-dried, but easy enough to approximate if you know the size 
and length of the recording.  Some folks have been able to do a single 
playback stream over 802.11b if they set the capture resolution & 
bitrate low enough.  802.11g (if you have the hardware & drivers) is 
likely good enough for a playback stream or two, but if you plan on 
having multiple backends & frontends, you really should go with at 
least 100Mbit wired ethernet.  Also, if you have any backends (master 
or slave) that record to an NFS-mounted directory, you'll have to 
account for that in you network bandwidth calculations.


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