[mythtvnz] Budget Myth spec

[Stephen Worthington]

On Tue, 10 Jun 2008 15:32:03 +1200, you wrote:

>I was just cruising pricespy and couldn't help but notice the price of
>potential myth boxes is suitably small these days.
>
>AMD 4800+ = $99 - retail
>Asus M2N-VM HDMI = $121
>2gb ram = $50
>320GB Seagate = 86.60 or 500GB WD = $112 both 7200 16
>Pick you DVD Writer = $40
>Case as you wish <$90
>Tuner $100-140 depending on what you go with
>all up 589 with 320Gb or just over 600 with the 500.
>
>I don't have any personal experience with the nvidia integrated HDMI
>but anecdotal evidence online suggests its good.
>
>If only I had 2 thirds of a grand to play with... and the time.

If the M2N-VM is similar to my M2NPV-VM, it has an Nvidia 6150 GPU
inside it, which is capable of doing SD video just fine.  As for HD,
we do not know yet as Nvidia have not released Linux drivers that do
H.264 in the GPU yet.  The current drivers do MPEG2 in the GPU, so the
CPU load for doing SD video is very low.  Using the Nvidia Vista
drivers on my Asus G1S notebook (Nvidia 8600M GT), the CPU usage is
also very low (< 5%) as the Vista drivers do do H.264 acceleration,
but whether the same will be true for H.264 on a 6150 chip is unknown.
In the mean time, HD output has to be done by the CPU, and an Athlon
64 X2 4800+ should be fine for that, as would a similar Core 2 Duo.

The other problem you need to consider seriously for a Myth box is
noise.  It is possible to put together a very cheap PC, but low noise
components are usually not quite as cheap.  Most people do not seem to
be bothered by the noise of a VCR operating next to their TV, but the
noise from a PC is noticeable and after a time becomes quite annoying.
I find that even a reasonably low-noise PC like my Myth box is
annoying at times.  I do not find the disk activity noise annoying
(the clicks of head movement), but the fan noise is a problem, and
possibly also the disk rotational noise although it is very hard to
distinguish that from the fan noise to be sure I am actually hearing
it.

So I think the ideal setup is to have a fanless frontend only PC by
the TV (one for each TV), and have the recording done by a
(relatively) noisy standard PC that lives somewhere else.  If you do
that, you would also need to factor in the cost of running aerial
cable(s) to the backend PC and Gigabit ethernet from there to all the
frontends.  I am not sure if anyone has a fanless PC that can do HD
display though - it takes a lot of CPU, or a grunty GPU, and those
need cooling.  There is no need for the frontends to have hard disks -
they can boot from CD or USB stick, or over ethernet.  The backend PC
could be a Linux box that is used for other things as well, as long as
it was set up correctly to give highest priority to recordings and
sending data to the frontends.

Modern DVD writers are *very* noisy as they rotate at extreme speeds.
So you do not want to use one to play a DVD from - you use it to copy
an image to hard disk and play from there.  So if you have an old slow
DVD, it might be better to use that in the Myth box and put the new
one in your old general purpose PC.  Or just temporarily put a CD or
DVD drive in the Myth box for doing installs, and do all the DVD
reading and writing on a fast DVD on your other PC and copy the files
over your Gigabit ethernet to the Myth box.

2 Gibytes of RAM is overkill for a Myth box (1 Gibyte is sufficient),
but RAM is so cheap now that you may as well have 2 Gibytes.

500 Gibytes of hard disk sounds a lot, but an hour of SD recording is
3.2 Gibytes using the hardware MPEG2 encoders in my Hauppauge PVR-500
tuners, and an hour of HD DVB-T is variable but IIRC it is around 5.1
Gibytes.  So more hard disk is better if you can afford it.  SD DVB-T
is much smaller - around 1.2 Gibytes per hour.  But SD programs are
becoming rare - almost all new programs are HD, as are most of the
ads.

To do Freeview DVB-T properly, you need up to three tuners, one for
each DVB-T multiplex, if you want to record from all three multiplexes
at the same time.  Each multiplex broadcasts on one old analogue UHF
TV channel, and sends multiple TV programs in parallel inside the
MPEG2 transport stream it broadcasts.  MythTV 0.21 has the multirec
feature that allows it to record up to 5 programs simultaneously from
one transport stream.  The hardware you are suggesting is easily
capable of recording four or more programs at once while also playing
back another - I do that regularly with my 4 analogue tuners on lesser
hardware (although I do have two 500 Gibyte hard disks).  That
presumes that the CPU is not doing encoding, as is the case for DVB-T
and when your analogue tuner has a hardware MPEG2 encoder.  The CPU
has to work much harder if you buy a slightly cheaper analogue tuner
that does not have the MPEG2 encoding built in - not recommended.