[mythtv-users] Dual HDTV Tuner Requirements

[Brad Templeton]

On Sat, Mar 05, 2005 at 01:05:19AM -0500, Jonathan M. Cooper wrote:
> I've been reading that HDTV decoding takes a substantial amount of
> processing power.  I was wondering if anyone has gotten 2 or more HDTV
> tuner cards working with myth, and, if so, what the CPU and memory
> requirements would be.  I'm considering replacing 2 UltimateTV boxes
> with myth.  The UltimateTVs each have 2 tuners, so I'd want a setup
> where I could record 4 shows at once (ideally).  That could be 2 boxes
> with 2 tuners or 1 backend with 4 tuners.

While Jarod answered your rought question, your wording belies the
common misconception about what the hdtv tuner cards do.   They
do almost nothing (they are only expensive because they are small
volume.)  They just receive a digital bitstream off the air, and your
PC does nothing but write it to disk.   It takes effectively zero CPU
to do this, you could fill your machine with cards and barely notice it
as it recorded 5 shows at once.

While the pchdtv-3000 also has a raw NTSC capture component (not yet
fully supported in myth) the ATSC tuner does nothing else.  It can't
take HDTV from a cable box or satellite box.  It can't encode mpegs
or decode them.    It can (just recently) receive non-encrypted digital
cable (a tiny fraction of the cable channels, but often including the
local HD ones.)

It's just a radio receiver and demodulator of a pre-compressed,
pre-encoded bitstream.

The UTV, like other boxes, has NTSC tuner cards including an mpeg
encoder for each tuner.   Your HD tuner card won't do this.  In
the future, proper support for the raw NTSC capture will be in
place and you could record NTSC -- but that will take CPU, a fair
chunk of it, to record to mp4, and so you probably would not be able
to record 2 mp4s, for example, and also watch hdtv, though right
now I have not heard anybody benchmark what it takes to do this.