[mythtv-users] Re: Hardware MPEG2 vs bt878

[Cory Papenfuss]

On Thu, 29 Sep 2005, Baudouin, Andrew wrote:

> Actually, believe it or not...
>
> All things equal a framegrabber will result in superior quality on-disk.
> The problem lies with the quality of the tuner on the cheap framegrabbers.
> It's clearly below that of the more expensive hardware cards.
>
> To preserve quality ideally you'd like to have the raw video on disk and
> compress it as you see fit rather than go straight into MPEG2.
>
>
 	"Everything" is not equal in this case.  The BT878 chip has 
inherently lower resolution for composite inputs (e.g. anything coming in 
via the tuner) than the SAA7115 or the CX--- that the PVR-[123]50's use. 
That has a much larger effect than the MPEG compression artifacts.  The 
MPEG artifacts can be effectively eliminated by cranking up the bitrate to 
lots... it'll still be more space efficient than RAW captures.

 	Since he's planning to use svid in an presumably an external 
demodulator, the difference may be less.  The lower resolution is the lack 
of comb filters... that's not used for s-vid inputs.  There are still some 
(optional) filters in the signal flow path.  One would have to ensure they 
were off.   The CX--- chip still has 10bit vs. 8bit for the BT878.

-Cory

-- 

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* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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