[mythtv-users] Firewire or capture card?

Rod Smith mythtv at rodsbooks.com
Thu Dec 24 19:16:31 UTC 2009

On Thursday 24 December 2009 01:02:20 pm steve wrote:
> My existing MythTV setup has crapped out (capture hardware failure) and I
> am starting over.  I want to get the new system set up to handle HD, and
> I'm trying to decide between doing a firewire connection to the cable box
> (SA Explorer 3250HD) and using a capture card.  The firewire option seems
> sensible, but I've been looking at the Wiki page on that and it sounds like
> a "challenging" setup.  Also the reports on the firewire cards flag a lot
> of cases where they don't work, don't support channel changing, don't
> stream video properly, etc.  So would I be better off using a dedicated
> capture card like the pcHDTV 5500?

I use both. Some key considerations include:

- What channels you get depends on your cable provider. Some encrypt
  everything coming off the FireWire port, making it pointless. Others
  send everything in the clear. Many encrypt the pay channels (HBO,
  Showtime, etc.) but leave others, including HD versions of basic cable
  (Syfy, Discovery, etc.), in the clear even if they're encrypted on QAM
  and thus untunable via a regular capture card. Try to find out what
  your cable company does.

- In my experience, FireWire isn't as reliable as a digital tuner. It's
  about 95-99% reliable for me, at least on the channels that work at
  all. Sometimes, though, it flakes out and stops working and requires
  one degree or another of a reset -- powering off the cable box and back
  on, futzing with drivers, or even a full MythTV backend reboot.

- You need support for your specific cable box. MythTV works with mine
  (a Motorola DCX3200-H), but when I set it up I needed to add its IDs
  to a separate tuner program (6200ch.c) and recompile it, then call a
  script that uses that program and runs some basic FireWire sanity
  checks to get it to work even at the 95-99% reliability I mentioned.

- At least some, and maybe all, cable boxes with FireWire ports include
  MPEG encoders, so you can use the FireWire/cable box combination to tune
  analog cable channels. Not all digital cards can do this, and some of
  those that do rely on the MythTV backend to compress the signal (to an
  MPEG-4 .nuv file, in the case of MythTV). Each approach has its advantages
  and disadvantages.

- You tune a cable box by the channel number used by the cable company.
  These numbers probably won't change very frequently. Some cable
  providers, though, juggle the underlying frequencies fairly often,
  so a straight digital tuner card may need to be reconfigured more

- Many regular digital tuner cards can tune multiple channels per
  multiplex, which can be handy if you want to record two shows that
  happen to be on one multiplex or if you want to pad two back-to-back
  shows on one channel. AFAIK, this isn't possible with a cable box and

- PCI (and perhaps PCIe) tuner cards sometimes suffer from interference
  from other computer components, resulting in dropouts. In some cases
  this can be quite severe; my pcHDTV 3000 card was next to useless in
  my original MythTV box, although it works fine in a slave backend.
  External tuners, such as the HDHomerun, are reportedly much less likely
  to suffer from such problems.

Overall, I prefer using my digital tuner cards to using FireWire, but my cable 
company only sends the locals and one or two others (CSPAN-3, for instance) 
in the clear, so an awful lot of my recording is done with my cable box and 
FireWire. I'm not entirely happy with this setup because of the reduced 
reliability and other limitations, but the only real alternative for me would 
be to shell out $200 or so for an HD-PVR.

If you can afford it, I recommend getting both a cable box/FireWire and a 
plain digital tuner card. That'll give you the best of both worlds, and 
you'll be able to record multiple channels simultaneously, so long as at 
least one of them is unencrypted. If you're strapped for cash and can only 
afford one at the moment, find out what channels your cable provider delivers 
in the clear, both directly (clear QAM) and over the FireWire port. If you 
don't get more via FireWire than you do in clear QAM, then IMHO there's no 
point in bothering with FireWire. If you get significantly more channels (and 
you want to watch them) over FireWire, then it's probably worth going that 
route, but be aware that you may run into serious problems that may require 
you to back out or swap your cable box for another model (if your cable 
company offers more than one).

Rod Smith

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