[ale] Lowest Power MythTV back-end?

[Phil Turmel]

On 11/20/2013 08:57 AM, JD wrote:
> On 11/20/2013 07:33 AM, Boris Borisov wrote:
>> Somebody in myth wiki reports for:
>>
>> Intel Atom N270 & Intel chipset
>>
>> Results are: 
>> Excellent with SD, and the menus perform great at 1080p.  Video at 1080p is un-watchable.

The key here is un *watchable*.  Wimpy processors make crappy *front*
ends, unless you have a well-supported GPU doing the work.

> Thanks. I read something like that in the Myth-Wiki.
> 
> There is a HUGE difference between SD and HD recording. I don't have any SD
> recording devices that work anymore after the digital TV transition. Thank you
> congress and the FCC.  My "cable ready" TVs are, oddly, NOT cable ready anymore
> even with QAM tuners. December 1st, Comcast has announced (got a letter) they
> are encrypting all remaining QAM channels. BTW, I dumped cable last year.

I use Hauppage gear with great success.  The long-retired analog
(PVR-500) was great because it did all of the encoding in the card (with
dual tuners).  I set that bandwidth to ~1.5Mbit/s for decent quality in
SD.  (DVD 480p is usually around 6Mbit/s for comparison.)

I'm now using a Hauppage HVR-2250.  It still has the analog encoders if
I ever want to transcode old VHS tapes, but the twin tuners work great
with digital broadcast TV.  Most primetime Hi Def programs use 12 to 18
Mbit/s.

My old Pentium-D backend typically spends only 2-4% CPU when recording
two streams.  All the work is simply moving data onto the hard drives.
Modern hard drives handle ~100Mbyte/s, so they're just loafing along as
well.

> Found a blog from 2011 where someone was using an E8400 with 2 digital tuners
> and 1 front-end. He was using a cheap NAS.
> http://www.mlaronson.com/low-power-mythtv-architecture/arch-diagram  Claims it
> handles recording 4 hidef streams while one is played. Seems like a start,
> though I wonder how he can record 4 streams with only 2 tuners?

Digital broadcast TV has subchannels.  Once tuned to any part of a
channel, getting all the subchannels is just a demultiplexing operation.
 MythTV asked me how many simultaneous streams to support per tuner when
I configured the 2250.  Although they show up as many more "recorders"
than you actually have, MythTV knows how to juggle the shared tuners.

> I have these CPUs/MBs available:
> * AMD E350 - only 2G RAM; sips power 16W, quiet (no fans).
> * C2D E6600 - only 2G RAM; sucks power, very noisy (newer PSU needed)
> * C2D E8400 - plenty of RAM, good with power, reasonably quiet

All of the above should be fine as *backends*.

> I would prefer to keep using virtualization so a dedicated system is not
> required, but that has recently run into issues.  Since the tuners are
> networked, doing a build on one system, then just swapping the HDD into the
> other physical boxes should work fine.

Virtualization raises latency a bit, but probably not enough to matter
with networked tuners.  I would expect you to be fine.

The gotcha for some people is the limit on wireless bandwidth.  Peak
bandwith of 54Mbit/s for 802.11g can cause problems if somebody starts a
big internet download while others are trying to watch MythTV
wirelessly.  My permanent front ends are wired ethernet.

HTH,

Phil