[mythtv-users] High level system architecture questions

Ben Bargabus ben_b at ppdonline.com
Thu May 26 00:32:06 UTC 2005


Thank you for taking the time to reply, I have some comments and
questions embedded below...


<snip>
> 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.


My main goal in looking at MythTV is to create a multimedia network,
emphasis on the network.  I'd like all the source to be centralized and
have the thinnest possible clients at each point of media consumption. 
Ultimately I'd like to have a master backend and multiple slave backends
in my "media server room" along with six DTV receivers, two 400 disc DVD
changers, and a really healthy RAID box. (at some point I plan on
bringing HDTV into the mix but I'll avoid that end of the discussion for
now as it seems that the technology, on MythTV's end, is not mature
yet)  I'd like the settop boxes to be minimal, most likely diskless,
machines that simply request data from the backends and perform whatever
sort of decoding is necessary (via something like the PVR-350).  I would
have a DVD-ROM of some sort in each so that if I wanted to watch a DVD
not in the changers I could without walking all the way to the server
room and back but would primarily rely on the backends for all source
media.


> 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).


I'm fine with the idea of having multiple PVR-250s or even multiple
slave backends.


> Also--and probably more
> importantly--you lose much of the benefit of DVD.


This relates to another question I have.  With a DTV receiver connected
to the backend is the output decoded by the receiver, encoded by the
PVR-250, sent across the network, and decoded by the PVR-350 in the
frontend?  Is this the only solution if the receiver is connected at the
backend (obviously the specific hardware could change but I'm talking
about the decode, encode, decode sequence)?  I'm well versed in
computers but not very well in video so please excuse my ignorance for a
moment, is this because the output from the receiver is analog? (if it
were digital it seems that it would be much easier to just divvy it up
into packets and send it on its way)  Even if analog why not just a good
ADC on one end and DAC on the other?  Is this a
bandwidth/storage-capacity issue (and thus really relying on the
compression of MPEG)?


<snip>
> Therefore, you will lose
> quality--even if you can't do progressive display with your TV.


Is this noticeable?  highly noticeable?  Does this manifest as
pixelation or artifacts etc...


> 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).


Does this also apply to changing channels on "live" TV?  For example, I
change the channel on my DTV receiver connected to the backend of my
system, do I now wait several seconds for the content to appear?  That
seems like an unacceptable delay, if I were surfing through channels and
each press of the channel changer took several seconds to respond.


> (Note that Myth has
> no provisions for piping data directly to TV without a buffer, and there
> are no plans to add this functionality.)


Is this open source?  What language is it written in?  If I get
energetic enough I may fix that.  (I'm a programmer)


Thank you for your response, I look forward to your further feedback,
Ben.


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