INDEX:
DVD acronym
DVD regions
DVD software decoder
DVD hardware decoder
DVD playback assisting display adaptors
Alpha blending
Overlay surfaces and colorspace conversion
Interlacing
DeInterlacing - weave
DeInterlacing - BOB
DeInterlacing - adaptive
Hardware motion compensation
Hardware - iDCT
Video objects files
DVD-ROM DMA
Wide screen and letterbox
Anamorphic wide screen encoding
MacroVision


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 fearing the DVD. Since the DVD format is a digital medium, and so it 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 you were wondering), all the DVD titles come out as Region #1 and only then transferred to the various other regions. However, there are some titles that aren't 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 purpose 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 off the CPU and into the Card itself. Accelerator cards have two major types of acceleration, "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 since 1995.


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 a sort of 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. You will see that while everything in windows is 256 color while the DVD playback window is 24bit true color. Another upside to Overlays is that they can do hardware scaling (image stretching) to any size without taking any CPU power. They also use a bilinear 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, as 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, but 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 or objects move quickly within a scene. To deal with this, 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 or content recorded using interlaced video cameras). 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.


DeInterlacing - Adaptive (Progressive Reconstruction):
Some DVD Players can detect badly encoded video and reconstruct a progressive image where possible and use smart deinterlacing code where this isn't possible. This can improve image quality for badly encoded content but it can cause slight image quality loss when used with properly encoded progressive material.


Hardware Motion Compensation:
Some chipsets (Most cards available today) have Hardware Motion Compensation support. Motion Compensation is said to improve DVD decoding time by 30%.


Hardware iDCT:
iDCT stands for Inverse Discrete Cosine Transform. It is a mathematical formula used in DVD decoding. Certain display 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 MPEG file format, and one for Title playback (actual DVD movie sequence).


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 DVD Frequently asked Questions section for information on enabling DMA for your DVD-Rom drive.


Wide Screen and Letterbox:
As a rule, most 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 always. 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 resolution of DVDs, 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 aspect ratio by the DVD decoder.

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


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 TV Output chip causing distortions if you try to record the signal. Several cards can have their MacroVision code disabled using home grown 3rd party tools.