OT: Composite/Component [was Re: [mythtv-users] Re: Image quality, what effects it?]

[Rudy Zijlstra]

Jay R. Ashworth wrote:

>> 	?  I was basically referring to the quantity of data that had to be 
>>passed.  If it were true RGB (which it's not... probably a factor of 1/2 for 
>>4:2:2), 720x480 * 30fps * 3 colors * 8bits/color = 31MBps... that's a lot of 
>>data for a PCI bus.  Even with a 1/2 reduction for YUV and 1/2 D1 of 352x480, 
>>that's 7.5 MBps... still plenty.  Trying to do HDTV would require 
>>proportionately more.  That pretty much means it would have to encode to MPEG2 
>>(or MPEG4) on the fly to stream over the PCI bus.  Lots of embedded CPU power 
>>necessary for that... 4x-8x hauppauge I suppose.
>>    
>>
>
>Yeah.  The PcHDTV card is probably doing that.
>
>  
>
No, it is not. It is receiving a 2, 4,  8 or 16 VSB modulated MPEG-2 
Transport stream according to the ATSC standard and selecting the wanted 
PIDs out of it.
SW support is only for 8-VSB (the only modulation currently used on 
ATSC), which limits the TS to 19.4 Mbit/s. This means the card is 
specific for terrestrial ATSC. On a cable the signal is likely to be 
re-modulated in QAM-64. QAM-256 might also be used. Most cable companies 
use QAM for digital modulation and will not support 2 different 
modulation schemes at the same time. Also the ATSC standard (at least 
when last I looked at it) does not mandate any particular modulation 
when used over cable. For terrestrial use VSB is mandated. Sattelite 
uses QPSK (QAM-2) modulation.

Rudy