[mythtv-users] Capture sharpness

Jay Mallar jaymallar at gmail.com
Sun Nov 25 19:35:16 UTC 2007


Rod Smith wrote:
> On Sunday 25 November 2007 13:41:17 Jay Mallar wrote:
>   
>> I'm using a PVR-250 to capture TV via my DirecTV STB.  On my TiVo, I get
>> much better capture quality in terms of picture sharpness than I do with
>> the PVR-250.
>>
>> I can't seem to find anything that will allow me to control the
>> sharpness of the capture, is there a way to modify this?  or is this
>> just an indication that PVR-250's aren't as good as the Tivo captures?
>>     
>
> There could be any of several factors at work here; you've not provided 
> information on this critical information:
>
> - Is your TiVo a standalone (SA) unit or a DirecTiVo? If the latter, it will
>   produce better quality because it records the digital bitstream directly,
>   whereas MythTV records the decoded analog output from a set-top box, which
>   imposes an extra digital->analog->digital conversion cycle.
>   
My TiVo is an SA, a Phillips PTV-300 (rather old one).  It's also 
connected to another DirectTV STB (the same type, a SAT-B3) - the same 
way my PVR-250 connects.
> - What inputs are you using? S-video is better, composite is middle, and
>   coaxial (RF) is worst. If you're using S-video for your TiVo and RF for
>   MythTV, that could explain it.
>   
I'm using coax from the STB to the PVR-250 and the same for the PTV-300.
> - What are your quality settings? (Resolution and bitrate, mainly?) These
>   impact quality. SA TiVos also have quality settings, although they're
>   expressed as Best, High, Medium, and Basic, IIRC, and I don't know the
>   precise mapping of those to resolutions and bitrates.
>   
I've tried everything and nothing seems to improve sharpness here.  I've 
gone up to the max for min and avg bitrate.  The only thing these 
settings seem to affect is pixelation, especially for high-speed 
motion.  Right now I'm using 720x480 MPEG-2 PS at 4:3 set to 2200/9800.  
I've tried all of the settings on 
http://www.mythtv.org/wiki/index.php/Recording_Parameters and nothing 
seems to make much of a difference in sharpness.  I'll be glad to change 
it to something else if you have something better.
> - What type of DirecTV receiver(s) do you have? I've seen claims that they
>   vary in video output quality, so it's conceivable that you've got one with
>   better quality feeding your TiVo and one with worse quality feeding your
>   MythTV box.
>   
My PVR-250 and my PTV-300 are both connected in the same way, to Sony 
SAT-B3 via coax.  The signal is split off from my dish via a multi-switch.
> - Have you checked your cables? Loose or low-quality cables can cause
>   problems. (That said, the high-priced premium cables sold by many retailers
>   are overpriced scams, IMHO. Just be sure you're not using something very
>   old, frayed, or designed for the wrong purpose.)
>   
I've tried several cables, with no effect.
> These issues aside, I've never done a direct comparison of a TiVo to a 
> PVR-250, so I can't promise that the latter can equal the former in image 
> quality. I'd be surprised if the differences were huge, though.
>   
In my case, the difference is quite noticeable when comparing the two 
back to back (I have an A/B switch and can easily go back and forth).  
However, just looking at the PVR-250 captures, it's easy to tell the 
picture isn't sharp, especially in the details, even without comparing 
it to my TiVo.




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