are games slowed down by tv out?

[rudeboymcc]

hi. i've got a really bad graphics card (mx440) and i've got a tv connected to scart.

say i'm playing a game, and i'm watching the tv, will it be any faster if i only showed it only on one of the displays??

i thought that once the signal is shown on one, it's nothing to show it on the other so i had the monitor and tv showing the same thing, (no reason, just didn;t think i needed to minimise it on one). well?

[Sirber]

Maybe your card is "dual screening". Look in your driver or unplug the TV (svideo wire).

[rudeboymcc]

i'm not saying that it is any slower, i'm asking if it makes a difference. i can't really see a difference myself.

[Joe Fenton]

Do the math - a modern 3D card has a memory bandwidth that is usually somewhere between 2 and 20 GBytes per second. Just take the low end and say 2G/s. Now a typical TVout resolution is 720x480 with 16bit YUV data, so this is 720 x 480 x 2 x 29.94 (NTCS res and freq) = 19.736 MB/s.

So TVout would consume about (20M/s / 2G/s) or (20M/s / 2048M/s) which is 0.977% of the bandwidth. So on a modern card, you are using no more than 1% of the card's memory bandwidth to refresh the TVout channel. If the computer is feeding data to the card for TVout, that consumes some memory bandwidth plus some bandwidth across the AGP bus, but you can see from the first calculation that it's probably going to be small as well.

So, GENERALLY speaking, TVout shouldn't make a difference you would notice. The older the card, the larger the impact.

[rudeboymcc]

thats interesting i didn't know you could calculate video streams like that. wehre did you get the 16bit YUV from?

and 720 x 480 x 2 x 29.94 - the 720 x 480 is the resolution. the 29.94 is the frequency, where does the two come from?

sorry i know this doesn't really make a difference but i'm interested.

[Joe Fenton]

Most older video cards display video data of the form yuyv. This mode has 1 byte of Y (luminance) data, 1 byte of u (chrominance) data, another byte of Y data for the next pixel, and 1 byte of v data (more color data). You get two luminance pixels and 1 color pixel which is twice as wide - this gives you half the horizontal resolution in color, but most people never notice this. So you have four bytes of data for two pixels, or an average of 2 bytes per pixel. That is where the 2 comes from.

To be REALLY technical, the output is 720 x 240 x 59.94 fields in an interlaced format. TVs use interlaced signals at twice the rate. The effective rate is 720 x 480 x 29.97. Then remember that each pixel needs two bytes. Newer cards support other modes like yv12. Yv12 gives half the horz res PLUS half the vert res for color, which works out to an average of 12bits per pixel, or 1.5 bytes per pixel instead of 2.

(Note, I put 29.94 before... it's 29.97 - for NTSC)