[mythtv-users] What hardware do I need to be able to dual record using Comcast cable?

Dewey Smolka dsmolka at gmail.com
Thu Oct 16 04:56:36 UTC 2008


On Wed, Oct 15, 2008 at 8:23 PM, Adam Rosenfield <adamrose at mit.edu> wrote:
> Hi all,
>
>  I have Comcast digital cable service.  Ideally, I'd like to be
> able to record any channel I can get normally through the Comcast
> set-top box in HD for HD channels,

Any Comcast subscription should give you the OTA stations in your
market in HD via a QAM-capable tuner. The Myth gold-
standard for this is the HDHomerun, which also tunes OTA ATSC from an
antenna. I think it still runs about $150, and is capable of two
simultaneous streams which go into your Myth system via ethernet. CPU
demands for recording are negligible.

The HDHomerun will only get you the unencrypted OTA channels unless
your local Comcast has not yet started encrypting the rest, in which
case you're lucky but don't count on it lasting. You feed the cable
straight into the HDHomerun without a converter box. You need to split
to get both tuners working.

You can also record the same OTA HD channels via firewire from the
converter box but that is only provided that:

A) your local Comcast will give you a compatible box -- you need an HD
box such as the Motorola DCT6000 series, which Comcast is loath to
give you unless you sign up for an HD subscription (an additional
$5-10/mo on top of the $5 they'll want for the box itself. You can get
one without the subscription, but be prepared for some long and
difficult phone calls. It helps if you can mention a few names on your
local PUC or other regulatory body, and bring up your willingness to
ask local regulators about FCC regulations and compliance and so
forth. Google is your friend.

B) The box you get has an operational firewire port -- they guys who
do the Cable install have no idea what you're talking about. Neither
does  the person who answers the phone (who apparently can neither
tell you their full name nor the geographic location of their call
center). If it's not working, you'll have to go through much the same
process as above to get it turned on. Mentioning the head of the local
cable regulatory body tends to get you a manager pretty quickly;

c) You have the patience and fortitude to get it working. Things have
undoubtedly improved, but as of about 18 months ago I was utterly
unable to get firewire working stably or at all consistently from a
DCT6200. There is a lot that can go wrong between having the right
card, the drivers, kernel modules, configuration, crash behavior, and
so on.

D) You'll need a separate box for each channel, and either a separate
input for each box or the cleverness to figure out how to daisy-chain
firewire devices. It can be done, as people who have done it will tell
you, but just adds complication to an already difficult task.

E) You don't mind the fact that your box rental charges will cost you
more than an HDHomerun within about 18 months.


There is also the new Hauppage HD-PVR, which is exciting but still
highly experimental. This transcodes the analog component output of an
STB into H.264, which means for each channel you'll need a separate
STB and a separate HD-PVR. And you'll need a big-ass processor to do
the decoding since consumer video cards do not yet support hardware
decoding. And you'll need to be comfortable enough with both Linux and
MythTV to compile and run the bleeding-edge development Myth code. And
if all of those were true you probably wouldn't be asking.

In short, your best option for multiple channels in HD is the
HDHomerun. Easy, painless, Works more or less out of the box and does
exactly what it says it will.

 > If I'm piping the streams right
> from the STBs, it's all digital, so I only need a digital capture
> card, right?

As far as the HD channels go, yes -- except you're not piping them
from the STB (unless you go with the HD-PVR), you're caturing the MPEG
streams directly off the cable or over the air.. For all the rest you
actually still want a hardware-encoding analog card, although I gather
these are becoming harder to find. A Hauppage PVR500 will let you
capture two simultaneous streams over composite, RF coax, or S-video
from an analog source, such as an STB.

You'll need a separate STB for each input, and you'll also need a way
to control each box -- either directly via serial port (same warnings
as above apply to explaining to Comcast what a serial port is and why
you need one), or via IR blaster. And while the PVR-500 only uses one
PCI slot, you'll need to mount an auxiliary bracket to use both
inputs.

> I doubt my CPU (a Pentium 4) can handle software HD
> encoding, let alone dual encoding.

Recording is trivial to your CPU if you use hardware devices like the
HDHomerun and the Hauppage PVRx50/500 series. The processor is really
only directing traffic. The heavy CPU lifting comes on playback. With
an Nvidia graphics card (even the cheap ones) you can use XvMC to
support the CPU in HD and SD decoding. As a purely anecdotal
benchmark, my BE/FE is a P4 2.5 with an nvidia 5200 card (PCI, not AGP
(don't even get me started on Compaq)).

SD is never an issue. It can record HD with no problem, and plays back
fine as long as no other hefty jobs are happening. Mythfilldatabase,
com flagging, transcoding, etc, cause unwatchable playback, and nice
doesn't really help. On the other hand, I can watch an HD recording in
progress while all channels are recording without incident.

I've also got a FE with an Athlon x2 4800+ (can't remember if it's 64
or not, but running 32-bit). It never has a problem with HD playback,
no matter what else it's doing (although I've never tried to find the
limit).


>
> With that in mind, are there are specific capture cards you would
> recommend?  My motherboard can only handle PCI, no PCI-Express.

Hauppage PVRx50/500 for SD capture. Some models come with IR blasters,
which are fully supported. You may also want to have a look at the
Microsoft MCE Remote (hey, other than music players and exploding
consoles they make pretty good hardware), which has dual IR blasters
(although I have a hazy recollection that may be untrue that both
blasters send the same signal and you have to configure each STB to
recognize its own signal).

HDHomerun for HD capture. The setup is simple, although it helps to
have a windows box on hand when you install it. The auto-scan in
Mythtvsetup is good but it doesn't always catch everything. The
utility exe that comes with it is very useful for mapping channels not
picked up in the auto-scan, and for general diagnostics and
troubleshooting. You'll only use it when you initially set the unit
up.

Check the wiki for specifics, search the archive if you have problems,
and good luck.


More information about the mythtv-users mailing list