[mythtv-users] Newbie Questions
mark at hethos.org
Fri Dec 15 22:53:43 UTC 2006
On Saturday 16 December 2006 06:12, dat220 at tappin.ca wrote:
> >> 1.) Digital vs. Analog Cable
> Why no HDTV? Shaw has a HD tuner available. So you are saying MythTV
> can't record HD content?
Myth can do HDTV, but it can't do decryption. As I understand it, the output
of cable boxes for HD tends to be encrypted. You can of course get it from
the analog outputs, but it is then no longer HD.
(I don't know so much about cable since I live in the wonderful land of
Australia, we use DVB cards, that pull an MPEG2 stream off the air. We get
HDTV off the air unencrypted as well. Since it comes down in mpeg2 straight
off the card, there is very little CPU usage, the backend just streams it
onto the disk).
> > 3.) Front End vs. Back End
> So the front end box sits next to your TV and you stream the recorded
> content from the backend? I am bit confused as to where each component
> (tuner cards, TV out cards, disks etc are placed).
Mythtv has what I would call a "network transparent architecture". You can
have multiple "backends" and multiple "frontends". A backend in this case is
a machine with a tuner (and some disk space). In my case I have a 1Ghz
celeron with a boatload of disk space in what I guess you'd call the
basement. But potentially you can have as many backends as you have tuners.
Also the one machine can be a backend and a frontend, but you then don't have
the separation of tasks (and the resultant advantages). In any case, any of
your machines can utilise the tuners of any of the other machines. Usually
there is a "masteer backend" which runs scheduling, and downloads your
From the backend in the basement, I have a PC hooked up to the TV upstairs
(via 100mbps ethernet). This machine is soon to be replaced with a diskless,
fanless, solid state machine that boots via the network. And herein lies the
advantage of the seperate frontend/backend. The backend has to be fast enough
to stream the content to disk, and over the network, but it's video
performance is irrelevant. The frontend doesn't need to have much in the way
of I/O performance, but it's video performance must be ok (or it needs
accelerated MPEG2 decoding). The backend (Which is louder) is on all the time
recording TV shows (it's also my internet gateway, so it's on anyway).
Another advantage is that my UPS is hooked up to this machine. My UPS is
ugly, and I wouldn't put it in my living room. The machine in my living room
can potentially be the size of a cdrom drive, boot in hardly any time, whilst
also being perfectly silent. Thanks to the VIA EPIA line of boards, and
I also have some other frontends, including a laptop. So I can wander out on
the back deck and stream tv off the backend. (wireless isn't always up to the
bandwidth of this).
I hope that my description of the backend/frontend system gave you a better
idea of how it works (rather than confusing you more) ;-)
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