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While setting up a DVD Player once typically involved procedures and settings similar to these, these suggestions are probably not relevant to current  Blu‑ray players. For example they say nothing at all about HDMI, even though it is now ubiquitous.
Consider this webpage to be an archive, retained because it may be historically interesting and may occasionally be informative about technological background relevant to some weird edge cases.
I wanted my new DVD Player to use the same flat screen that I use for my PC. (I don't have a TV, and I didn't want to get one. I don't have space for a larger screen. And I wanted to spend as little money as possible.) First I had to connect up all the wires to share the monitor with my computer. Next, the setup (configuration) of the DVD Player was a little trickier than usual because of the PC monitor sharing. Below are the details of what I did to get it working.
These steps were of course performed on a specific (and now quite old) DVD Player. The DVD Player I once used was an iView‑102DV (also called an IView 102). (This particular DVD Player happened to be region free, but that didn't affect either the monitor sharing or the setup.)
Once I got everything working, I found this setup is not only region free, but plays PAL format DVDs too. (While some region free DVD Players also do internal conversion so the monitor always receives an NTSC‑like signal regardless of how the DVD was recorded, many simply send the unchanged PAL‑like signal from the DVD on to the monitor. Although most newer digital monitors will correctly display this PAL signal, many older or analog primarily‑NTSC monitors won't.) Regardless of the details of exactly how it works in my setup, the bottom line is I can reasonably obtain DVDs from lots of different places, which expands my options (U.K. and Japanese eBay & Amazon, Hong Kong and Korea, etc.).
I also had some issues with the DVD Player itself which did not seem to be closely related to its setup.
Most DVD Players use an On Screen Display (OSD). Usually this works pretty well. But when connecting the video through a switch-adapter and using progressive scan, it can be tricky. You can't change the setup settings until you can see them on the screen, but you can't see anything on the screen until you get at least a few of the setup settings tuned to your environment.
This is a Catch-22 situation!
A possible secondary problem is the DVD Player may link some options to other options, so you sometimes change more than you would prefer. For example resetting a DVD Player to either NTSC or PAL may also change it to interlaced (even though it was previously correctly set to progressive).
It is reasonably possible though, even with less capable equipment. (Some fancier displays will automatically adapt to interlaced-or-progressive, so you need to get fewer settings right before you can see something. Only a few settings are critical for being able to see something on the screen (after which it's straightforward to tune the rest of the settings). These critical settings are S-Video/Component, NTSC/PAL, and interlaced/progressive.
You can change these few things even though you can't see the screen yet.
(Note: Usually interlaced scan or progressive scan will be dictated by your equipment and you will have no choice in the matter. Below there's a fuller description of interlaced and progressive.)
DVD Players may send their video signal out either their S-Video port or their Component Video ports, but often not both at the same time. If one is selected, the other may propagate errors, garbage, or even no signal at all.
You may be able to get around this initially by moving one of the conectors on the back of the DVD Player from the Y Component Video port to the Composite Video port (so the DVD Player's composite‑video output is connected to the switch-adapter's Y component‑video input), then disconnecting Pr or Pb or both.
Once you can read the on screen display —even if it's pink or blurry or torn or flickering— you can set everything you need to. It's unpredictable when this will happen; you might need to proceed with all the steps below before you finally get visual feedback. But be ready for this at any time; as soon as you can see the on screen display, all the rest of the steps will be much easier.
Depending on what country you're in, all TV signals may use either the NTSC format or the PAL format. (There are some other formats, but they're not very common, and not relevant to DVD Player setup.) You need to make your DVD Player send its signal in the same format your monitor expects. Once correct, the N/P setting very seldom needs to be changed again.
Likely your monitor expects signals in the same format TV uses in your country. In theory DVDs may contain information in either an NTSC‑like or a PAL‑like format; in practice though all DVDs commercially available in your region almost certainly match the format TV uses in your country. Only if you obtain DVDs from other parts of the globe for your region free DVD Player might NTSC/PAL be an issue. Some DVD Players do a decent job of converting formats internally, so you can watch a PAL DVD on an NTSC monitor, or vice versa (assuming region restrictions have also been dealt with).
(Both NTSC and PAL are interlaced analog TV formats. NTSC typically has 525 vertical lines and shows 30 frames per second [actually 60 interlaced half‑frames], which meshes with 60Hz electricity mains systems. PAL typically has 625 vertical lines [576 visible] and shows 25 frames per second [actually 50 interlaced half‑frames], which meshes with 50Hz electricity mains systems. NTSC was the first standard and was originally used for black-and-white signals; PAL is mostly about a more accurate method of impressing color information on an analog broadcast signal. NTSC is used for example in the U.S., while PAL is used for example in Australia.)
(In the DVD world, size and frequency vary and so are more important to users, while the exact method of encoding color and other information remains constant and invisible. So NTSC is used to mean pretty much the same thing as 480i, [525 visible and invisible lines at 60 half‑frames per second], while PAL is used to mean pretty much the same thing as 576i, [625 visible and invisible lines at 50 half‑frames per second]. This is a reasonable and useful common usage of these terms, even though in a strict sense the terms actually refer purely to analog signals [especially encoding methods].)
It's pretty easy to tell which format you need. If the format is right, the monitor will usually display something (maybe garbage). If the format is wrong, no harm will be done, but the monitor will be all black, not displaying anything at all.
You can set this even when you can't see the On Screen Display. A button labelled N/P on the remote control will flip back and forth from one format (NTSC) to the other (PAL). Press and release N/P; if the screen changes from all black to something (even garbage), you can stop as the setting is now correct; but if the screen changes from something to all black, put it back the way it was by pressing and releasing N/P again. If the screen was all black both before and after pressing the button, try continuing below, then if it doesn't work, press the key once more and try again.
The same setting is also available via the On Screen Display in the Preferences category as TV Mode", which may be either NTSC or PAL. (Don't mix this up with the other setting also named TV Mode but in the Video category.) Setting this through the OSD may be more convenient ...if you can see the OSD at this point.
Broadcast TV uses interlaced scan (first draw every other line, then go back to the top and draw the missed lines) while computers typically use progressive scan (draw every single line in order). By quickly drawing half the picture while the other half stays the same (and the half‑picture persists, originally because of slow posphor), interlaced scan can produce a less jerky picture where bandwidth is tightly constrained, and is less subject to having the picture completely obliterated by a burst of broadcast interference. Progressive scan can produce a crisper picture on larger screens if bandwidth and interference are not issues. Type of scan is what the letter on the end of resolution specifications is about: 1080p is progressive while 1080i is interlaced.
You need to make your DVD Player send its signal in the manner your monitor expects, which for a computer monitor is virtually certainly progressive It's pretty easy to tell which format you need. If the format is right, you will be able to (sorta) read the monitor. If the format is wrong, no harm will be done, but the monitor will just display completely illegible bands of gobbledygook colors.
(A complete format specification would include i line/dot/pixel counts in both directions (or count in just one direction and also the aspect ratio), ii whether the scan type is progressive or interlaced, and iii the frame rate. In most cases once a couple things are specified, the rest either default or are handled automatically and don't need to be explicitly stated; thus a format is often written as simply something like 1080p. The most commonly needed additional specification is frame rate; unfortunately how to write it isn't entirely standardized. You may see for example 1080p24, but you may also see 1080/24p or even just 24p.)
You can set this too even when you can't see the On Screen Display (assuming you've already correctly set NTSC or PAL). A button labelled V-MODE on the remote control, in conjunction with the button labelled ENTER, controls interlaced or progressive. Press and release V-MODE, wait a second, then press and release ENTER; if the screen changes to something you can read, you can stop as the setting is now correct. (On the iView‑102DV if you key V-MODE but don't follow by keying ENTER, your instruction won't be complete and nothing will happen.)
If it still doesn't work, try (slowly) pressing the buttons a couple more times, as V-MODE probably cycles through not only interlaced and progressive but also S-Video and YUV. As a result it may take four (rather than just two) presses to return to the original setting.
The same setting is also available via the On Screen Display in the Video category as TV Mode, which may be either P-Scan or Interlace. (Don't mix this up with the other setting also named TV Mode but in the Preferences category.) Setting it through the OSD may be more convenient ...if you can see the OSD at this point.
Your ultimate goal is to set Component to YUV (not S-Video) on the On Screen Display, and connect the three Component Video ports on the DVD Player to the three ports on the switch-adapter. If you haven't already got there, do so now.
After you get the On Screen Display (OSD) fully working, you may need to go a little further and adjust the video Brightness and Contrast settings in the OSD, perhaps to positive or even double-digit positive values. These settings may default to zero, which on some monitors may be rather dim.
Initially use the N/P and V-MODE (with ENTER) buttons to get to the point where you can at least read the On Screen Display. (The OSD may still be pinkish or torn or in some other way not perfect; all that matters at this point is that you can at least read it.) Then use the normal method with the OSD to perfect some parameters and set the rest.
Very annoyingly, initially my iView‑102DV DVD Player frequently exhibited lots of problems: freezing a whole picture, freezing a repeated horizontal band from a picture, stuttering, some picture blocks behind several frames, video and sound out of sync, settings randomly resetting themselves to zero, skipping a whole chapter, and so forth. Although it quickly became clear a few of these problems were due simply to dirty rental DVDs, the majority of the problems were apparently due to internal overheating as they only occurred after the DVD Player had been on for several hours. As the iView‑102DV is a half size unit (i.e. the components are packed in tightly), and as —like most DVD Players— it has no fan, overheating problems seemed quite likely. Indeed, some areas of the outside of the DVD Player sometimes became almost too hot to touch.
I resolved the overheating by separating the DVD Player from other equipment, placing it on top of a laptop cooler with three USB-powered fans, using some self-adhesive foam weatherstripping from the hardware store to seal the laptop cooler to the DVD Player so the fresh air is forced in through the vent holes on the bottom right of the unit, and taping over half the vent holes on the right side to force more air through the entire unit and out the left side vent. (Of course since the DVD Player doesn't have a USB port, I also had to obtain a separate USB Charger to power the laptop cooler. Only pay a couple dollars for such a unit, even though commonly prices are ten times higher. Really inexpensive units likely provide notably poor voltage stability ...but they're good enough to run fans.)
The greatly improved cooling entirely eliminated random loss of settings, the case being hot (or even warm), erroneous picture blocks, stuttering, sync problems, and skipping. Freezing (including a horizontal band as well as an entire picture) is considerably less frequent and less severe, but still occurs once or twice every third or fourth rental disc, especially when viewing a movie in slow‑motion (and maybe more frequently when viewing a movie multiple times). My understanding is these occasional freezes are almost inevitable with inexpensive DVD Players of this vintage, as such players tend to be hypersensitive to disc read errors (especially when converting NTSC Interlaced Scan DVDs to Progressive Scan output.)