[mythtv-users] colour "sharpness" question

Michael T. Dean mtdean at thirdcontact.com
Thu Oct 19 17:42:18 UTC 2006

On 10/19/06 09:25, Brian Wood wrote:

>  On Oct 19, 2006, at 12:40 AM, Michael T. Dean wrote:
> > Higher bitrate means bigger files, which means fewer hours of TV
> > fit on your system. With a hardware encoder (i.e.
> > PVR-x50/PVR-500), there's (practically) no other effect on system
> > resources.
> >
> > Note, though, that with the PVR-x50's/500's, having an average
> > bitrate over 6000kbps is probably a waste. As a matter of fact,
> > you're likely to hit the electronics' quality ceiling by 4500kbps
> > or so (assuming a good quality input signal). Just make sure you
> > have a reasonable maximum bitrate (about 133% the average bitrate).
> > The default for PVR's is 4500kbps average and 6000kbps max.
>  You might find this informative:
>  http://www.mediachance.com/dvdlab/tutorial/bitrate.html

Which, I'm sure you'll agree, is an excellent resource if it's not taken 
too literally.  Everything on the chart is exactly right as long as the 
bitrate values at the bottom are fuzzed out.   The chart doesn't factor 
in signal quality (a dirty signal will require more bitrate than a clean 
signal), variable bitrates (as discussed in the text, so read the text, 
too), encoder quality, and, most importantly, decoder/filter/other 
electronics' quality (that's the NTSC signal decoder used during 
capture, not an MPEG-decoder used during playback).

Also, since NTSC's resolution is limited, even if you use 720x480 
capture resolution (which is a good idea for DVD archiving purposes), 
you aren't getting same same quality as you would see in a 720x480 DVD 
(even if that DVD contains interlaced video).  Now, if you can keep the 
signal from ever becoming NTSC (which is impossible with a PVR-x50), ...

 From my experience (and from my interpretations of some good writeups 
by Cory Papenfuss), I still stand by the 4500/6000 being a good bitrate 
for PVR-x50's.  However, if you're mastering DVD's from original 
sources, that chart--and the bitrate values it shows--is probably 
exactly what you'll need.  :)

But, it doesn't hurt anything--except available storage--to use more 
bandwidth than required.


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