[mythtv-users] Preparing for HDTV in 2005

[Michael Hartman]

Sorry for not having this thread follow the official thread. I
subscribed to the digest and I can't hit the "reply" button :(

>> You can rule out recording from the component/S-video ports. Doing
>> MPEG2 HD encoding real-time in a consumer device is not really
>> feasible at this time.
>
>That would surprise me, since the pvr-250 seems to have no trouble with 
>480p..  twice that wouldn't be very hard for a company to do.  S-video 
>(and component) is nowhere near hdtv quality.  I'm talking about a card 
>that would look to the box as if it was an HDTV (say, via a dvi input
>port)
>
>But you're right, it might be too costly to implement on a consumer 
>level, for not enough quality savings due to the reencode.

Well 480p is a whole lot less bandwidth compared to 720p or 1080i. 
Don't forget that it is not only the lines that are increasing in size:

440x480p = 211,200 (pixels/screen) * 60Hz(progressive) =  
   12672000 pixels/sec

1280x720p = 921, 600 (pixels/screen) * 60Hz (progressive) = 
   55296000 pixels/sec

1920x1080i = 2,073,600 (pixels/screen) * 30Hz(interlaced) = 
   62208000 pixels/sec

As you can see, higher HD rates require at least 5 times the bandwidth. 

>> Besides, even if you could do real time encoding, you would not
>> really want to since the quality of the re-encoded stream would be 
>> sub-par.

>How (other than the resolution) is this different than using a pvr-250? 
>      Quality is quite good even at 480p, if I understand its users 
>correctly.

Well, what are you recording with the pvr-250? Was it content that was
previously encoded with MPEG2? If so, what bit rate did the origional
stream use? Something lean line 2Mbit/sec? Artifacts that arise from
MPEG2 decoding do not compress well. 

I'd rather keep the stream digital until it goes to the display device. 

>> One solution would be to have the set-top box output the un-modulated
>>  MPEG2 data somehow. How would it do this? Firewire. In fact, the FCC
>> has mandated that all set-top boxes made after April 2004 include
>> firewire ports.
>
>Wrong.  The FCC regulation applies only to HDTV-capable CABLE boxes. 
>Satellite companies are unaffected.

Sorry, I only subscribed two days ago to this list and didn't read the
entire thread. 

>> Mostly hardware companies are just putting firewire ports on their
>> stuff to make the FCC happy. I would imagine that getting your new HD
>> plasma TV to work with your HD dish box via the firewire port would
>> be an exercise in futility.
>
>the firewire ports weren't meant as an interface to the tv (that's not 
>what firewire is for) -- that's what DVI and other 1080p-compatible 
>ports are for.  firewire only gives you 480p, anyway, and not HD.

Wrong. I work in the cable TV industry. I design the hardware. This is
exactly why the FCC put firewire ports on the set-tops. It was meant to
transfer MPEG data to the TV so it could decode it. Don't forget that
the FCC also mandated that ALL TV's made after July 2007 will have DTV
tuners. DVT tuner not only means a VSB demodulator, but also a MPEG2
decoder. 

I'm not sure why the FCC picked firewire over DVI, but they did.  It may
have been do to the fact that Silicon Image almost has a monolopy on the
signaling chips that DVI.  Another reason could be that when the FCC
looked into making rules years ago, DVI did not exist but firewire did.  
 
>> BTW - does anyone know if any of the VIA EIPA mini-itx boards can do 
>> real time HD mpeg2 decoding?
>
>Doesn't this dispute the first sentence you wrote?

No. Don't confuse decoding with encoding. Decoding is a much easier task
compared to encoding. Compare what kind of PC was required to do a full
MPEG2 software decode when DVDs came out. The same caliber machine has
no chance of doing a real-time MPEG2 software encode. 

I get the impression from the pcHDTV specs that it outputs MPEG2
compressed data. Something has to decode that data to display it. Either
a dedicated processor (nvidia cards) or software decoder. I'm wondering
if the EPIA has the horsepower to do a software MPEG2 decode of an HD
stream.