So, before we get into another syntax pissing contest and i am told I am talking out of my ass again, what exactly do you mean by "genlocked, synchronous 29.97 resolution with a 1:1 pixel-mapped input/output characteristic"?
If you mean that the signal is encoded by the video card to the television exactly as it would have been by the original broadcast, (i.e. field interlaced, correctly timed with the picture the exact same size as it would have been originally) then yes, the g400 can do that.
I'm not trying to be belligerent, just trying to clarify the common misconceptions about tvout cards and why the concent of a "perfect" output is for the most part impossible with consumer cards.
When I'm saying "perfect," I'm talking about an end-to-end system with pixel-clock synchronization every step of the way. The system would have to do the following:
- Cable company sends "broadcast" quality video down the wire.
- Capture card synchronizes (via a PLL) to the color-subcarrier and samples the pixels at an integer multiple of it. (i.e. genlocked capture for 1:1 pixel mapping and synchronous sampling)
- MPEG encoding/decoding is done buffered and stored to the drive.
- Playback would have to decode the MPEG, with enough buffers and time-base correction to insert any missing fields.
- Decoded fields would be put into the framebuffer phase-locked with the original color subcarrier frequency captured (which doesn't really make sense in a time-shifted world, since the notion of time is now defined to by the computer's internal clock)
- After this field is decoded and put into the vid card's framebuffer memory, the decoder would trigger the vid card to issue another field via a VSYNC.
- This RGB data would then be encoded according to the NTSC spec, with the color subcarrier phase-locked to the horizontal sync at frequency 262.5 time x the horizontal frequency of 15.73kHz)
- The vid card would then wait until the next field was decoded before scanning again... unless the decode was never accomplished. In that case the TBC-portion of the system would have to generate the missing field.
In a real system, everything is clocked together... in a general-purpose computer like that, it cannot be guaranteed. Thus, many things run at their own clock (close, but not phase-locked and often not even frequency-locked).
That's not necessary... I believe you. I do not agree that "cannot visually see a difference" equivalent to "perfect," however. My own card that I build for VGA->NTSC was as close to perfect as one could get (or so I thought). A few months back I had a discussion with another guy on here who corrected me on the fact that my HCLOCK was (strictly-speaking) not phase-locked to the multile of the color subcarrier... thus it wasn't perfect. Nevermind the fact that I can get higher resolution on my TV from my computer than through a high-quality DVD player... it's still not "standards-compliant" and "perfect."You can't get perfect,
But I can. When I get a moment today (i.e. get a moment when somebody is not watching something), I will do a capture and take some stills describing exactly what I am talking about above and post links to the pics here.
I grow weary of this.... :)
-Cory
************************************************************************* * Cory Papenfuss * * Electrical Engineering candidate Ph.D. graduate student * * Virginia Polytechnic Institute and State University * *************************************************************************
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