[mythtv-users] best method to performance tune?

[Bruce Markey]

Brian A. Vance wrote:
> It's probably safe to say that the primary goal of most MythTV'ers is to
> squeak the best possible performance out of the hardware they currently
> have.  So the question is this... 

You may be right that this is a common goal but it baffles
me ;-). The goal should be to get good enough quality that
you will enjoy watching the recordings. This can be done with
a cheap CPU but that's another topic.

> What is the best way to find optimal settings?
> 
> (I realize 'optimal' is an ambiguous term and depends on personal
> preferences.. i.e. resolution, clarity, sound quality, file size, etc..)

See http://www.mythtv.org/docs/mythtv-HOWTO-18.html#ss18.4
This was added to help with this process.

> - Do you start at the lowest possible settings for each compression type
> and just slowly bring resolution/quality up until your hardware just
> can't keep up? 
> (This can get very tedious as it's tough to make a determination on
> quality without taking a large sampling.  i.e 30 mins on different
> channels)

Start from an educated guess then move from there. If you
use LiveTV and watch the output of "top" you can test a
resolution in just a few minutes rather than recording a
half-hour show. Remember, LiveTV is really record and play-
back at the same time.

> - Are there ways of gathering dropped frame rates other than counting
> messages from the console?

The delaying to next trigger message are for the audio being
so far out of synch that it needs to reset. There are no
messages for individual dropped frames.

> Right now I just seem to be making stabs in the dark.  Seems that
> without making a huge matrix and keeping track of quality levels for
> each setting, my attempts are futile!
> 
> What are people's preferred methods?  Are there general guidelines when
> picking settings?

Yes ;-). My rule of thumb is to choose the highest resolution
from 18.4 where the CPU "idle" time in "top" averages at least
10% during record and playback (or live tv). Average of 90%
means that at some moments 75%, other times 105%. It is when
the CPU is pegged that frames are dropped. Some frame dropping
is tolerable as long as there are at least 24fps. So generally,
if there is an average of 10% idle time you won't notice
stuttering.

--  bjm