[mythtv] Poll: what CPU with Dual Tuners/PIP?

[Bruce Markey]

Larry Matter wrote:
...
> I did see a comment in the documentation that you need roughly 1GHz per
> tuner, but as was recently discussed, processor clock speed is not the
> best  measure of performance.  The 2GHz Athlon's aren't cheap so I was
> hoping I might be able to get by with, say, an AMD 2100 (1.73GHz) which
> seems to be where the price break is.

The biggest factor for CPU usage when recording with the
mpeg4 codec is the resolution you use for recording. The
bitrate also has a small impact. The assertion of 1GHz
per tuner is based on 640x480 with enough headroom to
avoid jitter. Realize that the max resolution of T... a
leading commercial recorder is 544x480. With the quality
of NTSC signals, you can throttle back the horizontal res
and without noticing much quality loss.

I have two tuners on a 1.2GHz AMD system and can record two
shows at 352x480 (the low quality modes for the two leading
products =) with little or no noticeable jitter. For one tuner
720x480 works just fine but is overkill in most cases.

So, 1.73GHz AMD may be on the borderline of 2 @ 640x480
but should do well at 544x480 and should certainly do 480x480
unless there is something else terribly wrong.

As for benchmarks, there used to be things like MIPS and
SPECmarks to compare different types of CPUs. However, the
vendors would cheat and design their chips specifically to
do well on the tests ;-). There are no common benchmarks
that the general public can use to understand the relative
performance (whatever that is ;-). Since we're talking about
the Intel instruction set only, there is a relationship
between a class of chips and there clock speed. There are
differences in the characteristics of different chips and
therefore performance is not linear. However, even if there
were a benchmark that was considered "accurate" (whatever
that means ;-) it still wouldn't reflect the specific
characteristics of mpeg4 encoding.

So, we can only estimate loose approximations and the only
scale I know that others will understand is clock rate. I'll
contend that a 1.7Ghz AMD CPU is somewhat faster than a
1.4GHz AMD CPU and accept the fact that it is not precisely
21.4% faster 8-).

--  bjm