Hi Sluggers.
Lachlan & I have four Myth TV FRONT-ends running on a multi-segmented
100Mb LAN from a Myth TV BACK-end Server with four DTV capture cards
(intend to go eight-way DTV card configuration soon). As those of you
that have Myth TV up and running already probably know, the FRONT-end
CPU / motherboard mix is important if not the most important component
to assure excellent live TV and HD Movie reproduction.
Currently our FRONT-ends are VIA based mini-ATX motherboards with VIA
CX700M technology, Integrated VIA UniChrome Pro II AGP Graphics with
MPEG-2 & MPEG-4 Accelerator on-board and 1GB memory DIMM (see http://www.mini-box.com/s.nl/sc.8/category.15/.f
for more information if your interested) which are 1.5GHz CPU fully
fan-less, hence no noise except for the 5.1 || 7.1 Audio components.
All FRONT-ends boot/use mini-Myth via PXE to download FRONT-end start
up code and to communicate to the BACK-end ( a AMD Athlon 64 X2 Dual
Core Processor 4200+ with 2Gb DDR2 memory). The majority of FRONT-ends
use PicoPSU-90 modules < http://www.mini-box.com/picoPSU-90?sc=8&category=13
> so that there is no noisy PSU, only a 12-15VDC 2.5A plug pack and
to keep the footprint and heat print all in a very small. I
especially find useful the USB 4 x 40 LCD character front display on
each FRONT-end which passes motherboard and BACK-end operational
information without disturbing non-technical viewers. Each FRONT-end
(except one) outputs to LCD HD progressive TV displays, some with
integrated optical 7.1 audio. One FRONT-end outputs to a standard
definition + 1080i (interlaced) portable LCD display, natively running
of +12V DC supply plug pack.
Surprisingly my Nokia N800 is a excellent media viewing platform, and
getting better with each passing week.
Our empirical testing shows that our FRONT-end(s) provide A1+
performance for anything less than full 1920x1080 full high definition
spectral representations. A lot of our discoveries used a fabulous
publication "Video Demystified by Keith Jack - ISBN 0-7506-7822-4) and
the use of a dedicated IP-TV box which looks like a mini-MAC and uses
embedded Linux <http://www.galaxymetalgear.com/Products/
3500IPTV.html> purchased to play with a year or so ago, an 500MHz
oscilloscope and other testing tools.
For HD (1080-p : 1920x1080 non-interlaced video in OLD-Speak) every
FRONT-end will need the equivalent of > 2.3GHz CPU (even if dual or
quad core) as Myth TV code is still procedural in essence (I intent to
vary parts of the source code to go the OpenMP option < http://openmp.org/wp/
> using the newly released GCC so that every core is used to its
fullest opportunistic strengths) as a experiment later.
It is hoped that using "OpenMP" on some highly process bound sections
of Myth TV code will allow usage of our current spec'd FRONT-ends,
without having to upgrade to the "just about to be released - if they
haven't already" newer mini-ATX motherboards with 2.5GHz CPU and
extended onboard copper heat piping. That is we would really like to
tune and prune all our FRONT-ends so that "not os new" hardware can be
employed for HD usage.
Being "fan less" or "noise less" by using our DIY heat sinking and or
using what is "off-the-shelf" is a major selection criteria for us.
We, like most people don't like $$$$ going down a black hole. POUM -
Purchase Once, Use Many is a call to arms for most we suspect, as it
should be IMHO.
So, based on our extensive testing (for what we had on-hand) if you
want reliable full blown 1080-p FRONT-end you will require something
of the following parameters (courteously provided by Lachlan Botticciho)
1. Live HDTV requires a 2.0GHz processor and a fast memory bus,
preferable PCI/PCIe capture card(s).
2. Full HD 1080p requires a 2.4GHz processor.
3. You should get graphics cards or integrated motherboards that
will help with MPEG 2 and MPEG 4 acceleration. These take the burden
off the CPU, otherwise your back to "noisy fan" FRONTends.
4. Remember that graphics chips that will do this acceleration
require drivers to support them.
5. The VIA CPU and Graphics chips don’t have the driver support
required currently to support HD acceleration.
6. You can’t get a CPU + Graphics card combo that will handle HD
without a FAN of some description.
7. The Linux OpenChrome drivers do not support MPEG2 and MPEG 4
acceleration in the newer platforms. Still a year or so away apparently.
8. From the various forum’s people who are running HD on a mini-itx
size system are using Low wattage AMD CPU’s with NVidia integrated
GPU’s.
For Combination FRONT/BACK ends; you will get 1080-P HD results using
anything based on 2.4GHz or greater CPU, fast PCI/PCie graphic card(s)
and input DTV capture cards. Interestingly, if your like us and hate
advertisements, then a dual or quad core combination FRONT/BACK-end is
the way to go, just make sure you invest more in raw memory (> 2GB
best) first. You want to avoid Disk I/O swapping, and anything that
detracts from the task of transforming/streaming content.
Our testing of BACK-end DTV capture cards interestingly show that the
best cards are those that have integrated RF amplifier matched
distribution circuitry typically SMD MOSFET based components, which do
not consume too many input db's - this is especially needs to be
considered as we are in a valley where TV reception normally is crap
(< 50dbm). Surprisingly DTV stations (especially ABC & SBS which we
had the most difficulty getting) just made available channels # 300
onwards which provide greater signal strength than the lower UHF/VHF
channels of yesteryear. We have a DTV tuned antenna, and distribution
box right at the antenna input, as well as further along the cable so
our location is rather the "best testing point for very marginal DTV
reception" which is why we have spent so much time and effort testing,
selecting and providing the best performers we where able to acquire.
Apologies for a bit of rambling, but I hope this adds some experience
to the discussions.
Cheers. Grahame
PS: I capitalised FRONTend and BACKend to clarify my discussion as
people (myself included) become confused at times, especially when
writing on a small screen profile of a N800 :)/
MythTV release: 0.21
mythFRONTend version: 0.21.20080304-1
Mini-Myth release: 0.21.0-62
Linux BACKend - Ubuntu 8.04.1 kernel 2.6.24-22-generic SMP--
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