DVD Technical Notes and Terms

DVD Acronym:
DVD stands for "Digital Versatile Disc" or "Digital Video Disc" take your pick.

DVD Regions:
The big movie companies who so far divided the world by the various T.V. standards (NTSC, Pal, etc...) started to fear the DVD. Since the DVD format is a digital medium and thus has no different broadcast standards for various world regions. So in order to discourage cross-country purchases of movie titles, they came with with the infamous Region Scheme. This scheme basically divided our small planet into six regions.
However, not all regions were created equal. Since 99.99% of the world film market is generated in the good old U.S. (which is region #1 if someone is wondering), all the DVD titles come out as Region #1 and only then transferred to the various other regions. However, not all titles are transferred, while others are modified and lose some of the perks that the original Region #1 title had.

DVD Software Decoder:
A program written to decode the DVD stream using your computer's CPU power alone.

DVD Hardware Decoder:
A specialized card created for the sole use of decoding DVD streams. These cards also include a Video->Out connection allowing you to view the DVD Streams on a T.V. These cost money. And usually double the cost of your DVD playback solution.

DVD Playback Assisting Display Adaptors:
These are display adaptors (VGA cards) that can assist with the playback of DVD titles to some degree. They do this by moving some of the mathematical process from the CPU to the Card itself. Accelerator cards can have two types of acceleration, either "Motion Compensation" or "iDCT" (Or Both). Some cards claim to have DVD acceleration, but in fact this is mostly hype. Chip makers claim they have "Packed to Planer" support and Alpha Blending. While these do accelerate DVD playback, it is not a new "DVD" specific feature. This feature was introduced to help MPEG-1 playback several YEARS ago, and 95% of the cards support it for at least a couple of years now.

Alpha Blending:
Alpha blending is usually seen in 3D gaming, it is used to place one texture over the other using transparencies. In DVD it is used to display smoother looking Menu selections and Subtitles. Some cards claim this to be DVD acceleration, and while it may be that, it will only give 1-2% speed acceleration, and only if you have subtitles visible.

Overlay surfaces and Colorspace conversion (Packed to Planer):
Your computer monitor uses a color system called RGB to display an image, however DVD and MPEG titles use a YUV system because it can be compressed better with less quality loss. The offside to this is that you need more CPU power to convert the YUV stream to RGB before it can be displayed on your screen. This problem was first introduced when MPEG-1 become popular. At that point various hardware vendors started to incorporate hardware YUV->RGB conversion into their cards. This hardware conversion was implemented into an Overlay design. An overlay is sort of a window that doesn't take your current color mode into account and always displays in 24bit true color. If your video card supports overlays you can see what i mean by switching to an 8bit (256 color) mode and playing a DVD title using CineMaster. You will see that while everything in windows is 256 color, the DVD playback windows is 24bit true color. Another upside to Overlays is that they can do hardware scaling of the overlay stretching it to any size without taking any CPU power. They also use a bi-linear stretching code which gives a smoother picture when stretching the image. Without a display adaptor that supports overlays, most of the DVD software decoders will simply not work, or work A LOT SLOWER taking a CPU hit because they need to do the YUV->RGB conversion themselves.

Interlacing:
Your T.V. screen does not work like a Computer Monitor. A computer monitor display is a square, it has fixed points at exactly the same distance from eachother both vertically and horizontally. However, your T.V. screen is interlaced, if you look closely at your T.V. screen, you will see that it is in fact a lot of small vertical Red, Green and Blue lines placed closely next to eachother. Not only that, these lines are slightly offset to eachother on each screen row. A T.V. also updates the image differently compared to a Computer Monitor. The final result is, when trying to play a T.V. image on a Computer Monitor, you will get visible horizontal streaking when the camera pans. To deal with this, DVD software decoders have come up with some DeInterlacing code (see below).

DeInterlacing - Weave:
Weave is the default mode that should be used when viewing progressive DVD data (Movies for example). Using this mode you will see horizontal streaking for non-movie data (NTSC/PAL content such as movie trailers). If you plan on viewing DVD movies, you must set your decoding software to weave mode. Weave is the default DeInterlacing mode all decoding software use for Movie playback (unless set to some sort of detection mode).

DeInterlacing - BOB:
T.V. playback works a bit differently compared to a computer monitor. It has two fields, each playing in an interlaced form at either 30 or 25fps (NTSC/PAL). When NTSC/PAL content is played on a computer monitor using the standard Weave DeInterlacing mode, you get a lot of horizontal streaking when the camera pans or objects move quickly within a scene. To combat this, you can use the BOB DeInterlacing mode. What BOB does is play the content at twice it's frame rate and each frame is displayed in only one of the fields. This makes the image appear to BOB up and down a bit, especially when text is displayed, but doing so eliminates the streaking. Using the BOB mode is only useful for NTSC/PAL content such as Movie Trailers. On Progressively encoded Movie content BOB will cause the image to look slightly blurred.

Hardware Motion Compensation:
Some chipsets (ATI Rage Pro, ATI Rage Fury, S3 Savage 3D) have Hardware Motion Compensation support. Motion Compensation is said to improve DVD decoding time by 30%. However, when using motion compensation, make sure to set the DeInterlacing mode to "Force Weave" when playing DVD Movie Titles. Otherwise it will actually slow down the DVD playback.

Hardware iDCT:
iDCT stands for Inverse Discrete Cosine Transform. It is a mathematical formula used in DVD encoding/decoding. Certain assistance cards have iDCT hardware. In combination with Motion Compensation, iDCT can accelerate DVD playback by moving approx. 70% of the DVD decoding process onto the card itself, allowing for smooth DVD playback on even a 200mhz MMX CPU.

Video OBject Files:
There are two formats for VOB files. One for file display which are the DVD version of the MPG file format. And one for Title playback (actual DVD movie sequence). Some players support playback of standalone VOB files (ATI v1.2 Player, Win98 Media Player, PowerDVD, Xing) while others support only DVD Titles (CineMaster Player - not the engine, the actual player).

DirectShow Drivers:
Under windows 98 and Win95 OSR 2+ a multimedia driver scheme was introduced to replace the old 16bit Media Player MCI interface. This interface is called DirectShow. And it's baseline interface is called Active Movie. Accessing active movie under Windows 98 is hard, but microsoft have released a new Media Player that uses DirectShow drivers. You can download the new media player from microsoft (if you can find it) or try getting it from Strouds, and possibly off some Tucows Mirror. Now, the new Media Player is just an interface to access the DirectShow drivers. What you need is a DVD DirectShow driver so you can use a front end program to play DVD VOB files and DVD Titles. To date, CineMaster and Xing are the more popular DVD Engines that are released as DirectShow drivers. That means, that once installed, you can use any DirectShow front end to play VOB files and DVD Titles. The Windows 98 DVD Player is just that. A front end for a DirectShow DVD driver. So once you install either Xing or CineMaster, you can use the Windows 98 DVD Player to play DVD titles instead of the Player that comes with either package. However, there might be a bit of clash with the region setting, im not exactly sure how the various front ends keep the region setting and how it can clash with the region setting kept by the decoding engine itself.

DVD-Rom DMA:
Without enabling DMA (Direct Memory Access) your DVD-Rom drive has to transfer all the data from the DVD to the computer memory using the CPU. This takes valued CPU time away from the computer and will cause massive slowdowns when trying to play DVDs (missing frames ...).
Check the Frequently asked Questions section at Inmatrix for information on enabling DMA for your DVD-Rom drive.

Aspect Ratio and Proportional Resizing:
Most Display Adaptors do not contain the exact resolution mode used by full-screen or wide-screen DVD Titles. To compensate for that, most DVD Players (PowerDVD 1.22 excluded) support Maintaining the aspect ratio when resizing the image. This is used to prevent image width/height distortion and as a rule should always be enabled, except for certain Wide-Screen titles (see "Anamorphic Wide Screen encoding").

Wide Screen and Letterbox Titles:
As a rule, all T.V. screens and Computer monitors maintain a Width/Height aspect ratio of 4:3 (4 pixels wide for every 3 pixels high). However, Movie titles don't follow this rule and are usually wider, mostly conforming to a 16:9 aspect ratio (16 pixels wide for every 9 pixels high), but not alwats. When viewing Wide-Screen or Letterboxed titles, you will notice that there are two black stripes above and below the movie image. Certain DVD titles contain both a Wide-Screen and a Full-Screen versions on the same DVD Disc, while others only contain one of the two. Some people detest watching Wide-Screen movies while others prefer it because the image is not truncated when converted to full screen by the DVD author. Another benefit of Wide-Screen is that if the title is encoded correctly (See Anamorphic Wide Screen encoding) it can be viewed on a wide-screen television without the black stripes.

Anamorphic Wide Screen encoding:
Anamorphic Wide Screen is a technique used to increase the vertical scan line thus improving the visual quality of wide screen encoded titles. It uses 33% more scan lines compared to normal encoding, and the resulting image is scaled back to the original size by the DVD decoder.

This method wastes less of the encoding space on the black lines usually associated with Wide Screen encoding.

For a more complete definition of Anamorphic encoding, check:
What's an Anamorphic DVD?.

MacroVision:
MacroVision was first introduced in Disney VHS Cassettes. If you ever tried copying Disney VHS Cassettes (illegal btw), you will get a very downgraded film quality with lots of flashes and color loss. I am not sure as to the actual mechanics of the MacroVision process but basically it alters the image signal so that it becomes impossible to record it on an analog VCR. The DVD Titles themselves can not be MacroVision encoded as MacroVision was designed for analog output.
All DVD Decoder cards and some T.V.->Out cards have MacroVision enabled, the signal the card delivers is altered in real-time by the Decoder card causing distortions if you try to record the signal. Several cards can have their MacroVision code disabled, this requires altering the driver code.

For more MacroVision information, visit the MacroVision FAQ.