[mythtv-users] Is there a good guide on recording profiles somewhere?

Bruce Markey bjm at lvcm.com
Tue Aug 31 16:29:59 EDT 2004


Cory Papenfuss wrote:
>> I've noticed a lot of people using high bitrates with the PVR-x50's, 
>> but I'm using a pretty low bitrate and getting what I consider to be 
>> excellent results.  I will admit that I'm coming from about 5 years of 
>> having only watched TV after recording everything to VHS in EP mode, 
>> so I'm not the best judge of quality (anything beats an EP VHS 
>> recording :).  Also, I have a satellite signal piped to the PVR-350 
>> via S-Video (but I'm using nVidia GF4MX440 for output for OpenGL and 
>> Xv support), so signal noise/bad signal quality aren't a problem.
> 
> 
>     I've also noticed that a lot of people have seemingly ridiculously 
> high bitrates/resolutions.  Of course you can't argue with, "It looks 
> better," but I don't trust myself to make such subjective observations.  

Agreed. I think it's a normal reaction for people to see that
they don't really like the picture at a medium res/reasonable
bitrate so they max out the only "quality" factors that they
are aware of. However, this is just more bits of the same bad
picture. The problems are more likely finding the black level
cutoff and max luma without blooming for the signal before
digitizing, chroma level alignment, signal quality and the
effects of noise on compression, etc. That plus any playback
issues as you pointed out such as the tv-out characteristics,
black level and blooming on the output device (TV set), scaling
of the image in an xv window inside an X session scaled inside
a tv-out raster. These all contribute to a disappointing image
and the reaction is to turn up the recording resolution in hopes
that it might make the picture better. 

I agree with your conclusions about the limited effective horizontal
resolution. Kell factor (http://www.ntsc-tv.com/ntsc-index-04.htm)
which will be different on different sets and other limitations
prevent higher resolution recording from looking appreciably
different than medium res (if that wasn't the case, then why not
record at 2048x480 ;-). Even if a higher res was slightly better
than medium res, it isn't much due the the law of diminishing
returns. Because of the poor trade off of a lot of disk space for
a little (if any) quality, commercial DVRs max out at 544x480 for
their highest quality.

>     "Poor quality" describes a multitude of sins.  I suspect that a lot 
> of quality problems people see are bad TVOUT on their vid cards.  My old 
> NVIDIA sucked mightily.

Exactly.

>     I still have yet to figure out recording profiles.  I managed to 
> make another table (localhost.localdomain), and now that's all it uses.  
> Sooner or later I"ll get tired of the condition of the box and redo it 
> from scratch... originally built in December '03 on RH9.  Three 
> different motherboards on the same install, but it's just never broken 
> to where I needed to do anything with it!

Now the myth user question which is why I'm replying ;-) The
initial sets for profiles for hardware encoders, software
encoders, etc. are used by default for every card of that type.
The abstraction is that you may want to record "Nova" at High
Quality (it really should say High Resolution =). If you have
a mix of cards, it is recorded with the profile for the card
type this is used so that it will be high for software or high
for hardware.

Say someone had two fast backends with software encoders and
a card 3 on a slow machine with a software encoder. If Nova
somehow got assigned to machine 3 it would not be able to handle
it. The "Create new profile group" would allow this user to
use different settings for the one slower machine.

If you have one machine and created as profile group for
localhost.localdomain (BTW it probably shouldn't allow localhost
because each machine would think the custom settings were intended
for itself) then your one machine would always use the custom
group and never the default group for the card type. In short,
you gain nothing, just move the effective profiles to a different
group name.

--  bjm



More information about the mythtv-users mailing list