[fackben]

I have a bunch of questions about viewing HDTV broadcasts on a computer.


1) Assuming I use a typical PC DTV card, for example the MIT MyHD card, I was wondering if a computer display is capable of displaying a 1080i (1920 X 1080) signal without scaling it and losing image quality? I'm also assuming that the maximum resolution that my monitor can run at is 1600 X 1200. If the image is scaled, how is the image quality affected?


2) Assuming my monitor is set at 60Hz, and mpeg2 video is 30 frames per second, does this mean that the monitor shows each frame exactly twice?

To complicate the question, now lets say my refresh rate is set at 85hz. Tell me if I'm wrong or not, but I'm assuming that each frame will appear on the monitor appear 2.83 (approx 85 / 30) times. A computer cant show certain frame only .83 times. So what actually happens?


3) Does the "raw" mpeg2 data being broadcast have any information about how it will be displayed? If there was such a thing as lets say a HDTV 720i broadcast standard, would it take any less bandwidth than a 720p broadcast?


Thanks,

 

[kwerner]

I don't have answers for you, but you might search through the HTPC forum or ask your question there...
http://www.avsforum.com/avs-vb/forum...?s=&forumid=26

 

[Dub Egbert]

Quote:

Originally posted by fackben I have a bunch of questions about viewing HDTV broadcasts on a computer. 1) Assuming I use a typical PC DTV card, for example the MIT MyHD card, I was wondering if a computer display is capable of displaying a 1080i (1920 X 1080) signal without scaling it and losing image quality? I'm also assuming that the maximum resolution that my monitor can run at is 1600 X 1200. If the image is scaled, how is the image quality affected? 2) Assuming my monitor is set at 60Hz, and mpeg2 video is 30 frames per second, does this mean that the monitor shows each frame exactly twice? To complicate the question, now lets say my refresh rate is set at 85hz. Tell me if I'm wrong or not, but I'm assuming that each frame will appear on the monitor appear 2.83 (approx 85 / 30) times. A computer cant show certain frame only .83 times. So what actually happens? 3) Does the "raw" mpeg2 data being broadcast have any information about how it will be displayed? If there was such a thing as lets say a HDTV 720i broadcast standard, would it take any less bandwidth than a 720p broadcast? Thanks,

I think you might be assuming your PC video card has something to do with the display of HD. It doesn't - the PC HDTV card drives the monitor directly (the display plugs into the HDTV card and not the video card). The computer video card also plugs into the HDPC card for display of video in a small (non-HD) window. Additionally, the video card settings that you quote are not limitations of your display.


Your computer display is probably better than any HDTV on the market. Without scaling, it will do a fine job of displaying 1920 x 1080 (assuming the display is not some old dog).


The vertical and horizontal scan rate is set by the HDTV card, e.g. 34 hz x 60 hz for 1080i, 45 hz x 60 hz for 720p and 31 hz x 60 hz for 480p - numbers are approximate). You, the user, selects the resolution in the HDPC card setup. The vertical scan rate (refresh rate) is 60 hz which is the rate required for all three forms of HD, i.e. a new picture every 1/60th of a second, or in the case of 1080i, a new frame every 1/60th of a second.


I use the AccessDTV HDPC card with a 21" monitor and also have a Mits 73909 HDTV and find the quality of the HD pictures essentially the same but with the AccessDTV having a slight edge.

 

[vruiz]

Quote:

Originally posted by fackben 1) Assuming I use a typical PC DTV card, for example the MIT MyHD card, I was wondering if a computer display is capable of displaying a 1080i (1920 X 1080) signal without scaling it and losing image quality? I'm also assuming that the maximum resolution that my monitor can run at is 1600 X 1200. If the image is scaled, how is the image quality affected?

CRT computer monitors do not do any scaling. They are multisync display devices, meaning they will sync and display any signal at any resolution that's within their specs. CRT computer monitors actually have better resolving capabilities than most consumer HDTVs currently in the market. The only limiting factor is the size. HDTV signals do look great on them.

Quote:

2) Assuming my monitor is set at 60Hz, and mpeg2 video is 30 frames per second, does this mean that the monitor shows each frame exactly twice? To complicate the question, now lets say my refresh rate is set at 85hz. Tell me if I'm wrong or not, but I'm assuming that each frame will appear on the monitor appear 2.83 (approx 85 / 30) times. A computer cant show certain frame only .83 times. So what actually happens?

Again, your monitor is not "set" at any refresh rate. Resolution and refresh rate are set by the computer video card, and the monitor will display almost any resolution and refresh rate that it's sent. In the case of HDTV signals, the HDTV card will be the one dictating what the monitor will display, depending on the signal being received (1080i or 720p), and regardless of the resolution that your main video card is set at. HDTV signals are always 60Hz, 30fps for 1080i and 60fps for 720p.

Quote:

3) Does the "raw" mpeg2 data being broadcast have any information about how it will be displayed? If there was such a thing as lets say a HDTV 720i broadcast standard, would it take any less bandwidth than a 720p broadcast?

Sure. The encoder at the originating transmitter dictates what type of signal is sent, and and the HDTV card will receive it and display it natively, or convert it to the format of your choice for display on non-multysinc devices (such as most HDTVs that can only accept 1080i).

 

[vruiz]

Quote:

Originally posted by Dub Egbert The vertical and horizontal scan rate is set by the HDTV card, e.g. 34 hz x 60 hz for 1080i, 45 hz x 60 hz for 720p and 31 hz x 60 hz for 480p - numbers are approximate).

You mean Kilohertz for horizontal scanning rate, not hertz. 480p is 31.5 Khz, 1080i is 33.75 Khz, and 720p is 45 Khz, all at 60 Hz.

 

[Dub Egbert]

Quote:

Originally posted by vruiz You mean Kilohertz for horizontal scanning rate, not hertz. 480p is 31.5 Khz, 1080i is 33.75 Khz, and 720p is 45 Khz, all at 60 Hz.

ooops!

(Happens when you get old and gumpy...)