[mythtv-users] High level system architecture questions

[Michael T. Dean]

Ben Bargabus wrote:

>Hello again,
>So as I'm planning my hardware purchases for my first system I have some
>questions about how this system is intended to be used, best used, and
>most commonly used (maybe all three are the same but most likely not).
>The vision I have in my head based off of the reading I've done on this
>list and in HOWTOs goes something like this...
>
>dss receiver   dvd changer
>    |            /
>    |           /
>    |          /
>    |         /
>    |        /
>    |       /
>    |      /
>MythTV Backend
>      |
>      |
>      |
>   Network
>      |
>      |
>MythTV Frontend
>      |
>      |
>     TV
>
>
>Using that system I imagine myself sitting in front of my television and
>making requests to the mythtv frontend (via my remote control) that
>access information on the mythtv backend.  In some cases this would be
>prerecorded content but may also be live broadcast from my DirectTV
>receiver or a movie from my dvd changer (I'd have a connection to the
>low speed data port on each of these from the mythTV backend to control
>them).  Is this possible, intended, common, best?  A second viable
>option I can imagine is something like this...
>
>dss receiver#1  dvd changer
>    |            /
>    |           /
>    |          /
>    |         /
>    |        /
>    |       /
>    |      /
>MythTV Backend
>      |
>      |
>      |
>   Network    dss receiver #2
>      |        /
>      |       /
>MythTV Frontend
>      |
>      |
>     TV
>
>In this scenario the first dss receiver would be used solely for
>scheduled recording whereas "live" tv viewing would be done via dss
>receiver #2 (also contolled via low speed data port).  Is this more
>realistic/less problematic or unnecessary because my first scenario is
>fine?
>  
>
Right, what you described is basically how it works.  In the first 
diagram, you have a dedicated backend and a dedicated frontend.  In the 
second diagram, you have a dedicated backend and a frontend/backend 
combo.  A third diagram could have a dedicated backend and dedicated 
frontend, but you could put both DSS receivers on the single backend 
(just put an extra tuner card in the backend).  (And, of course, there's 
the fourth diagram with a frontend/backend combo with the two DSS 
receivers connected directly to it--this is what I'm doing, primarily to 
limit the number of computers I have to keep running at all times (I 
currently have four with only one of them doing Myth things).)

One note, though, when it comes to your (standalone/set-top) DVD 
changer, you probably don't want to hook it into your Myth backend.  In 
order to integrate it into a Myth system, you'll have to connect it to 
an input on a tuner card.  Therefore, you would either have to have an 
extra tuner card (i.e. one more than the number of satellite receivers 
you have) or only watch DVD's when both tuners are not in use (i.e. when 
only recording one show or none).  Also--and probably more 
importantly--you lose much of the benefit of DVD.  All (non-high-def) 
tuner cards accept NTSC/PAL input.  Since NTSC/PAL are interlaced 
formats, piping DVD output (which can be progressive--depending on your 
DVD and DVD player) through the tuner card would eliminate the potential 
for progressive playback (assuming you have a nice-enough TV that 
progressive is an option).  Also, the MPEG-2 (lossy-format) encoded 
video would be decoded by your DVD changer, piped to your tuner card, 
encoded by your Myth box into another (lossy) format (i.e. MPEG-2 for a 
hardware encoder or RTJPEG or MPEG-4 for a software encoder), then 
decoded by your Myth box and output to the TV.  Therefore, you will lose 
quality--even if you can't do progressive display with your TV.  And, 
finally, there's the annoyance factor...  Since Myth would treat the DVD 
playback as just another "LiveTV" channel, it would buffer it (to allow 
you to pause, rewind, etc.).  Therefore, there would be a couple of 
seconds of delay between the time you pushed a button on your DVD remote 
until it "took" (i.e. when navigating DVD menus).  (Note that Myth has 
no provisions for piping data directly to TV without a buffer, and there 
are no plans to add this functionality.)

Therefore, your best bet for DVD's is to a) get a DVD-ROM or DVD writer 
for your Myth frontend and let it play the DVD's (this is the approach 
I'm using, and I think the output quality--especially when using 
post-processing--rivals, or possibly surpasses, that of even high-end 
DVD players) or b) connect the DVD-changer directly to the TV and use it 
for direct playback (meaning you'll need a slew of remotes to work the 
system and you have all the input-switching rules you have to teach 
people when they come over.

HTH.

Mike