TV-out FAQ

[ericball]

Since a TV is one of the ways of displaying MAME and some questions keep coming up, I thought I'd create a FAQ.  This FAQ is divided into two sections; the first dealing with standard TVs, the second dealing with digital TVs and HDTVs.

Comments & corrections welcome, though I would prefer those based on technical knowledge instead of simply personal experience and preference.

**** Standard TV ****

There are two major standard TV signal formats : NTSC (used in North America and Japan) and PAL (used in Europe).  PAL also has several variations (like PAL60), including SECAM (which is 625/50 like PAL, but has a different color signal).  There are variations of NTSC, but they are much less common.  Modern PAL TVs are often able to handle NTSC, while the same cannot be said of NTSC TVs.

Normal NTSC is 525 lines at 29.97fps (59.94fps interlaced), PAL is 625 @ 25fps (50fps interlaced).  This includes vertical blanking; only around 480 lines NTSC / 576 line PAL are really useable (which is what is used by a DVD) and some of those may be lost to overscan.  Some TVs are better than others in handling out of spec signals (too many or too few lines), but I suspect the TV-out on most graphics cards isn't capable of generating anything other than 525/625. 

Note: people who use 800x600 (or higher) for TVout aren't getting any additional vertical resolution.  However, some cards/systems don't seem to be able to go lower than 800x600.  Just be aware that anything above ~480/576 lines will have to be scaled down to <=480/576 for TV out. 

Suggestions to force less than 480 lines are probably to reduce the number of active lines to eliminate any overscan problems.

NTSC horizontal frequency is 15.734kHz, PAL is 15.625kHz (similar to a standard resolution arcade monitor).  Again, some TVs are better than others in handling out of spec signals, but I suspect the TV-out of most graphics cards is very close to the standard and not adjustable.

Horizontal resolution is a function of the pixel clock & blanking ratio.  So a DVD (720x480/576) uses a 13.5MHz dot clock, which gives a total line of 858 pixels.  And that 720 is optimistic and subject to overscan, 704 is more typical for onscreen.  Square pixel NTSC (640x480) has 780 pixels per line or a 12.27MHz dot clock. 

Composite NTSC will top out at 320/455x480 due to aliasing with colorburst frequency (3.57MHz) (and has lower color resolution).  S-Video NTSC limits the color resolution to 3.57MHz, but opens up the pixel clock.  RGB or other component (YUV or YCrCb/YPrPb) will have no restrictions on horizontal resolution other than the capabilities of the graphics card & TV.

In summary - 640x480 (for NTSC) is the best match for TV-out.  (768x576 for PAL?)  However, most modern graphics cards - especially ATI - do an extremely good job of outputting good quality TV pictures, so just go with what looks good.


**** Digital & HDTV ****

Digital TVs (LCD, Plasma, DLP) and HDTVs will be limited both by the connection type and the "native" resolution of the display.

If you connect a DTV/HDTV like a TV (via S-Video or composite TV-out), then it won't look much better than a TV.  (Depending on how much de-interlacing etc the DTV/HDTV has.)  The trick is to understand what the DTV/HDTV is best at and how to take advantage of it.

Okay, one big assumption: we're talking about a true HDTV with 720p or 1080i resolution, not some widescreen TV which has only 480/576 lines.  In that case you are best sticking with 640x480 or 853x480 (1024/576 for PAL?) for 16:9.

HDTV has two 16x9 hi-res modes: 1280x720@60fps (or 720p) and 1920x1080@30fps interlaces (or 1080i).  Not all HDTVs can display both modes, but rather they use scaling to display the other.  Most HDTVs will also upscale other resolutions (e.g. 480i or 480p) to a higher, preferred or native, resolution for display.

If you connect your PC to the HDTV via TV-out then you are, in effect, converting whatever resolution the game is in to 640x480i to send it to the HDTV.  The HDTV then will upscale, and probably deinterlace, that to fit it's preferred display mode.  Some graphics cards may support progressive output, which means avoiding deinterlacing artifacts.

If you connect the PC to the DTV/HDTV with a VGA or DVI cable, then the PC will either scale the game to fit the DTV/HDTV's resolution or the DTV/HDTV will scale the resolution used by the PC to it's preferred mode.  Good for vector games, okay for high res (VGA) games, but not so good for medium and standard res (EGA & CGA) games.

Okay, to summarize:

• DTV/HDTVs will scale and probably deinterlace to suit their preferred display mode.
• The less scaling and other modifications which get done to the signal the better.

Therefore connect the DTV/HDTV via VGA or DVI and have the PC use the HDTV's preferred resolution.