[mythtv] hardware needed to smoothly record a show while watching another

Bruce Markey mythtv-dev@snowman.net
Thu, 12 Dec 2002 15:27:45 -0800

Peter M Schuh wrote:
> Hi-
> I've read through the mailing list and the documentation, but I haven't
> seen any direct answers to this question:
> What hardware does it take to record a show on one channel while watching
> another channel (and preserving the ability to pause the one that's
> being watched)?

If I'm reading your question correctly, it takes two tuner
cards. One to "record a show on one channel" and one for
"watching another channel". MythTV does support recording
with two cards at the same time. However, in the current
version I think you can only watch the show being recorded
on the first card while it is being recorded. I don't
believe you can record just one show and watch the ring
buffer for the second tuner. Anyone, please correct me if
I'm wrong about this.

> Does anyone have this working?  If so, let me know what CPU, RAM and tuner
> cards you have.  Does the hardware MPEG support make enough of a
> difference that one can have a slower CPU (or is it not implemented well
> enough yet).  The docs say that an AMD 1800+ can "almost" do this, but I'm
> curious what actually does do it.

The resolution and bit rate affect how much CPU is needed.
The example in the docs is based on 640x480 at 3300bps.

I have a test machine with a 1.2GHz AMD, GForrce4 440MX,
and two WinTV cards. With this setup, I can record two
shows while watching a recording without pegging the CPU by
using a resolution of 352x480. By using a lower horizontal
resolution, the picture is a little blurrier (but not twice
as bad ;-). Each encoding takes about 35%-45% CPU. Decoding
at this resolution takes (surprisingly) less than 2%. At
the MythTV default setting of 480x480 decoding takes ~17%
CPU. I'm guessing the hardware scaling is optimized for
352 which matches a standard. Again, clarifications welcome.

I'd infer that any CPU over 2GHz should be able to handle
two recordings at 640x480 and one playback at the same time.

--  bjm