[mythtv-users] quality

Michael T. Dean mtdean at thirdcontact.com
Tue Sep 12 14:03:12 EDT 2006

On 09/12/06 12:27, Sergei Gerasenko wrote:

>I'm running MythTV 0.18 on a box with an nvidia card, a 19" Dell 1950FP
>LCD and a PVR-150. When MythTV is running full screen (1280x1024),

First, you shouldn't use 1280x1024.  You need square pixels for 
everything to work properly in Myth.  So, if you have a 4:3 display, you 
should use one of 640x480, 800x600, 1024x768, 1280x960, ...

Of course, on a 1280x1024 LCD, sending one of these resolutions will 
result in the LCD scaling everything--which could negatively impact 
quality.  So, basically, the LCD you have isn't ideal for Myth.  Using 
it at 1280x1024, you probably won't see much in the way of issues, but 
just keep this in mind:  you have various tradeoffs to consider.

> the
>quality is kinda bad. From a distance, it looks pretty decent though. I
>understand that the "native" resolution of the PVR card is 480x480.

Basically, the problem isn't so much the PVR.  It's the signal it's 
being fed.  NTSC (the US standard for TV signals) is > 50 years old 
(from 1953 in its current form (allowing color TV)).  PAL (the standard 
used by pretty much everyone else) is about 40 years old (from about 
1967).  Once a signal goes NTSC/PAL, loss of quality is expected (and, 
since the PVR's only take NTSC/PAL signals...).

> If
>I'm planning to watch TV mostly on the LCD, what's the best way to
>increase the quality? Reduce the gui size? 
Go to a digital broadcast form (i.e. ATSC or, for you, probably DVB).  
High-definition digital is your best bet.

Other things you can do include:
    - Use a different resolution.  While the electronics of the PVR-x50 
and the signal prevent much quality difference at > 480x480 capture 
resolution, some cards have problems with other resolutions (i.e. at 
least some versions of ivtv drivers gave very poor quality for 
PVR-150's/PVR-500's at any resolution other than the max--i.e. 720x480 
(NTSC) or 720x576 (PAL)).
    - Modify the recording bitrate.  You should have long surpassed the 
maximum quality at about 6000kbps with a max of 8000kbps or so, but 
probably will get pretty much the same quality at about 4500kbps 
average/6000kbps max.  Both of these bitrates assume a recording 
resolution of 720x480 (NTSC) or 720x576 (PAL).
    - Check/improve signal quality.  See 
http://www.gossamer-threads.com/lists/ivtv/devel/17953#17953 .
    - Others that I can't think of right now...  Meaning trial/error are 
your (soon to be much hated) friends.


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