It's important to understand the difference between DVD-Video and DVD-ROM. DVD-Video (often simply called DVD) holds video programs and is played in a DVD player hooked up to a TV. DVD-ROM holds computer data and is read by a DVD-ROM drive hooked up to a computer. The difference is similar to that between Audio CD and CD-ROM. DVD-ROM also includes future variations that are recordable one time (DVD-R) or many times (DVD-RAM). Most people expect DVD-ROM to be initially much more successful than DVD-Video. Most new computers with DVD-ROM drives can also play DVD-Videos.

The following details are for audio tracks on DVD-Video. Some DVD manufacturers such as Pioneer are developing audio-only players using the DVD-Video format.

A disc can have up to 8 audio tracks (streams). Each track can be in one of three formats:

• Dolby Digital (formerly AC-3): 1 to 5.1 channels
  
• MPEG-2 audio: 1 to 5.1 or 7.1 channels
  
• PCM: 1 to 8 channels.

Two additional optional formats are provided: DTS and SDDS. Both require external decoders and are not supported by all players.

The ".1" refers to a low-frequency effects (LFE) channel that connects to a subwoofer. This channel carries an emphasized bass audio signal.

Linear PCM is uncompressed (lossless) digital audio, the same format

DVD has the capability to produce near-studio-quality video and better-than-CD-quality audio. DVD is vastly superior to videotape and generally better than laserdisc. However, quality depends on many production factors. Until compression experience and technology improves we will occasionally see DVDs that are inferior to laserdiscs. Also, since large amounts of video have already been encoded for Video CD using MPEG-1, a few low-budget DVDs will use that format (which is no better than VHS) instead of higher-quality MPEG-2.

DVD video is compressed from digital studio master tapes to MPEG-2 format. This "lossy" compression removes redundant information (such as areas of the picture that don't change) and information that's not readily perceptible by the human eye. The resulting video, especially when it is complex or changing quickly, may sometimes contain "artifacts" such as blockiness, fuzziness, and video noise depending on the processing quality and amount of compression. At average rates of 3.5 Mbps (million bits/second), compression artifacts may be occasionally noticeable. Higher data rates can result in higher quality, with almost no perceptible difference from the master at rates above 6 Mbps. As MPEG compression technology improves, better quality is being achieved at lower rates.

Video from DVD sometimes contains visible artifacts such as color banding, blurriness, blockiness, fuzzy dots, shimmering, missing detail, and even effects such as a face that "floats" behind the rest of the moving picture. It's important to understand that the term "artifact" refers to anything that was not originally present in the picture. Artifacts are sometimes caused by poor MPEG encoding, but artifacts are more often caused by a poorly adjusted TV, bad cables, electrical interference, sloppy digital noise reduction or picture enhancement, poor film-to-video transfer, film grain, player faults, disc read errors, etc. Most DVDs exhibit few visible MPEG compression artifacts on a properly configured system.. If you think otherwise, you are misinterpreting what you see.

Dolby Digital is multi-channel digital audio, compressed using AC-3 coding technology from original PCM with a sample rate of 48 kHz at up to 24 bits. The bitrate is 64 kbps to 448 kbps, with 384 being the normal rate for 5.1 channels and 192 being the normal rate for stereo (with or without surround encoding). The channel combinations are (front/surround): 1/0, 1+1/0 (dual mono), 2/0, 3/0, 2/1, 3/1, 2/2, and 3/2. The LFE channel is optional with all 8 combinations. Dolby Digital is the format used for audio tracks on almost all DVDs.

MPEG audio is multi-channel digital audio, compressed from original PCM format with sample rate of 48 kHz at 16 bits. Both MPEG-1 and MPEG-2 formats are supported. The variable bitrate is 32 kbps to 912 kbps, with 384 being the normal average rate. MPEG-1 is limited to 384 kbps. Channel combinations are (front/surround): 1/0, 2/0, 2/1, 2/2, 3/0, 3/1, 3/2, and 5/2. The LFE channel is optional with all combinations. The 7.1 channel format adds left-center and right-center channels, but will probably be rare for home use. MPEG-2 surround channels are in an extension stream matrixed onto the MPEG-1 stereo channels, which makes MPEG-2 audio backwards compatible with MPEG-1 hardware (an MPEG-1 system will only see the two stereo channels.) MPEG Layer III (MP3) and MPEG-2 AAC (aka NBC, aka unmatrix) are not supported by the DVD-Video standard.

DTS (Digital Theater Sound) is an optional multi-channel (5.1) digital audio format, compressed from PCM at 48 kHz at up to 20 bits. The data rate is from 64 kbps to 1536 kbps. Channel combinations are (front/surround): 1/0, 2/0, 3/0, 2/1, 2/2, 3/2. The LFE channel is optional with all 6 combinations. The DVD standard includes an audio stream format reserved for DTS, but first-generation players ignore it. A few demo discs were created by using a "fake" PCM track containing DTS audio (this is the same technique used with CDs and laserdiscs). These are the only DTS DVD discs that work on all players. New DTS-compatible players and official DTS discs using the proper DTS audio stream will arrive in mid 1998. DTS-compatible players will carry an official "DTS Digital Out" logo. Some manufacturers may provide upgrades to make existing discs comaptible with DTS discs. According to DTS, existing DTS decoders will work with DTS DVDs. Note: All DVD players can play DTS audio CDs. For more info visit < http://www.dtstech.com>.

SDDS (Sony Dynamic Digital Sound) is an optional multi-channel (5.1 or 7.1) digital audio format, compressed from PCM at 48 kHz. The data rate can go up to 1280 kbps. Sony has not announced any plans to support SDDS on DVD.

THX (Tomlinson Holman Experiment) is not an audio format. It's simply an additional set of processes applied by THX-certified surround sound amplifiers. "THX 4.0" processing is added to Dolby Pro Logic: crossover sends bass from front channels to subwoofer; re-equalization on front channels; timbre matching on rear channels; decorrelation of rear channels; bass curve that emphasizes low frequencies. "THX 5.1" processing is added to Dolby Digital and improves on 4.0: rear speakers are now full range, so crossover sends bass from both front and rear to subwoofer; decorrelation is turned on automatically when rear channels have the same audio, but not during split-surround effects, which don't need to be decorrelated.

Discs containing 525/60 video (NTSC) must use PCM or Dolby Digital on at least one track. Discs containing 625/50 video (PAL/SECAM) must use PCM or MPEG audio or Dolby Digital on at least one track. Additional tracks may be in any format. A few first-generation players, such as those made by Matsushita, can't output MPEG-2 audio to external decoders.

The original spec required either MPEG audio or PCM on 625/50 discs. There was a brief scuffle led by Philips when early discs came out with only two-channel MPEG and multichannel Dolby Digital, but the DVD Forum clarified in May 1997 that only stereo MPEG audio was mandatory for 625/50 discs. In December 1997 the lack of MPEG-2 encoders (and decoders) was a big enough problem that the spec was revised to allow Dolby Digital as the only audio track on 625/50 discs.

For stereo output (analog or digital), all players have a built-in 2-channel Dolby Digital decoder that downmixes from 5.1 channels (if present on the disc) to Dolby Surround stereo (i.e., 5 channels are matrixed into 2 channels to be decoded to 4 by an external Dolby Pro Logic processor). PAL players also have an MPEG or MPEG-2 decoder. Both Dolby Digital and MPEG-2 support 2-channel Dolby Surround as the source in cases where the disc producer can't or doesn't want to remix the original onto discrete channels. This means that a DVD labelled as having Dolby Digital sound may only use the L/R channels for surround or "plain" stereo. Even movies with old monophonic soundtracks may use Dolby Digital -- but only 1 or 2 channels. Sony players can optionally downmix to non-surround stereo.

The Dolby Digital downmix process does not usually include the LFE channel and may compress the dynamic range in order to improve dialog audibility and keep the sound from becoming "muddy" on average home audio systems. This can result in reduced sound quality on high-end audio systems. Some players have the option to turn off the dynamic range compression. The downmix is auditioned when the disc is prepared, and if the result is not acceptable the audio may be tweaked or a separate L/R Dolby Surround track may be added. Experience has shown that minor tweaking is sometimes required to make the dialog more audible within the limited dynamic range of a home stereo system, but that a separate track is not usually necessary. If surround audio is important to you, you will hear significantly better results from multichannel discs if you have a Dolby Digital system.

All five audio formats support karaoke mode, which has two channels for stereo (L and R) plus an optional guide melody channel (M) and two optional vocal channels (V1 and V2).

A DVD-5 with only one surround stereo audio stream (at 192 kbps) can hold over 55 hours of audio. A DVD-18 can hold over 200 hours.

Many people complain that the audio level from DVD players is too low. In truth the audio level is too high on everything else. Movie soundtracks are extremely dynamic, ranging from near silence to intense explosions. In order to support an increased dynamic range and hit peaks (near the 2V RMS limit) without distortion, the average sound volume must be lower. This is why the line level from DVD players is lower than from almost all other sources. And so far, unlike on CDs and LDs, the level is much more consistent between discs.

[1.19] Is DVD-Video a worldwide standard? Does it work with NTSC, PAL, and SECAM?

DVD-V has the same NTSC vs. PAL problem as videotape and laserdisc. The MPEG video on DVD is stored in digital format, but it's formatted for one of two mutually incompatible television systems: 525/60 (NTSC) or 625/50 (PAL/SECAM). There are three differences between discs intended for playback on different systems: picture size and pixel aspect ratio (720x480 vs. 720x576), display frame rate (29.97 vs 25), and surround audio (Dolby Digital vs. MPEG). (See 3.4 and 3.6 for details.) Video from film is usually stored at 24 frames/sec but is preformatted for one of the two display rates. Movies formatted for PAL display are usually sped up by 4%, so the audio must be adjusted accordingly before being encoded.

Some players will only play NTSC discs, some players will only play PAL discs, and some will play both. Most European players play both. These multi-standard players output NTSC from a 525/60 disc and PAL from a 625/50 disc. This requires two TVs or a multi-standard TV. Some players partially convert NTSC to 60 Hz PAL, which requires a 60 Hz PAL TV. It's also possible to make a standards-converting player that will output standard NTSC from a 625/50 disc or standard PAL from a 525/60 disc, but no such players have been announced.

A producer can choose to include additional video and audio --at the expense of playing time-- so that all formats are covered. It's unclear if players will be able to automatically recognize and play the correct video track. Of course it's always possible to put 525/60 video on one side of the disc and 625/50 on the other. Most studios so far are including Dolby Digital tracks along with the MPEG audio tracks on their PAL discs.

There are actually three types of DVD players if you count computers. Most DVD playback software and hardware can play both NTSC and PAL video.

Most DVD players have the following output connections:
Video:
- Composite video (CVBS) RCA/Cinch (NTSC or PAL)
- Y/C (s-video) (NTSC or PAL)
Audio:
- Dual RCA stereo analog audio (with Dolby Surround encoding)
- Digital audio (IEC-958 Type II RCA coax [S/P DIF] or EIAJ CP-340 optical [Toslink]). Raw digital audio (AC-3, MPEG-2, PCM, or optional DTS or SDDS) requires an external decoder or an amplifier/receiver with built-in decoder. (Note: The digital AC-3 audio output is not the same as the RF AC-3 output on laserdisc players.)

Some players may have additional connections:
- Component analog video, NTSC or PAL (YUV: 3 RCA connectors, RGB: SCART connector or 3 RCA)
- RF video output for connecting via channel 3 or 4 to TV without direct input. (Panasonic DVD-A300, RCA 5500P)
- 6 RCA jacks for analog surround sound output. (Panasonic DVD-A300, RCA 5500P, Samsung DVD905)
- AC-3 RF output on combo LD/DVD players. LD AC-3 on RF output only, DVD AC-3 on coax/optical outputs only. (Pioneer DVL-90, DVL-700)

Some players and receivers support only S/P DIF or only Toslink. If your player and receiver don't match, you'll need a converter such as the Midiman C02.

Most of the DVD players with component outputs use YUV, which is incompatible with RGB. European players with SCART connectors have RGB outputs. YUV to RGB transcoders are rumored to be available for $200-$300, but seem hard to track down. A $700 converter is.

Note: The correct term for analog color-difference output is Y'Pb'Pr', not Y'Cb'Cr' (which is digital, not analog). To simplify things, this FAQ uses the term YUV in its generic sense to refer to color difference signals.

No DVD players have yet been announced with digital video outputs, but it's expected that at some point digital output will be available using FireWire (IEEE 1394) connectors (see < http://firewire.org>).

[3.2] How do I hook up a DVD player?

It depends on your audio/video system and your DVD player. Most DVD players have 2 or 3 video hookup options and 3 audio hookup options. Choose the option with the best quality (indicated below) that is supported by your video and audio systems.

Video

• Component video (best): Some U.S. and Japanese players have component YUV video output in the form of 3 RCA or BNC connectors. Connectors may be labelled YUV, color difference, YPbPr, or Y/B-Y/R-Y, and may be colored green/blue/red. Some players have RGB component video output via a 20-pin SCART connector or 3 RCA or BNC connectors labelled R/G/B. Hook cables from the three video outputs of the player to the three video inputs of the display, or a SCART cable from the player to the display. Note: For equipment with RGB inputs, the YUV signal won't work; a transcoder is required. Converters from s-video are also an option; contact Markertek Video Supply, 800-522-2025. (Note: There is an unsubstantiated rumor that the Toshiba SD-3006 component outputs have poor color conversion.)
• S-video (good): Almost all players have s-video output. Hook an s-video cable from the player to the display (or to an A/V receiver that can switch s-video). The round, 4-pin connectors may be labelled Y/C, s-video, or S-VHS.
• Composite video (ok): All DVD players have standard RCA (Cinch) baseband video connectors. Hook a standard video cable from the player to the display (or to an A/V receiver ). The connectors are usually yellow and may be labelled video, CVBS, composite, or baseband.
• RF video (worst): A few players have RF video output for televisions with only an antenna connection. Connect a coax cable from the player to the TV. A 300 ohm to 75 ohm adapter may be needed. Tune the TV to channel 3 or 4 and set the switch on the back of the player to match. Audio is supplied with the RF signal, but it's only mono, even on stereo TVs. If you have a player without RF output, you can buy an RF modulator (~$30) to hook up to an old TV with RF input only. You can also route the video through a VCR, but this will usually cause picture problems with any disc that's Macrovision protected.

Warning: If you connect your DVD player to a VCR and then to your TV, you may have problems with discs that enable the player's Macrovision circuit. This usually shows up as a repeated darkening and lightening of the picture.

Note: Most DVD players support widescreen signalling, which tells a widescreen display what the aspect ratio is so that it can automatically adjust. One standard (ITU-R BT.1119, used mostly in Europe) includes information in a video scanline. Another standard, for Y/C connectors, adds a 5V DC signal to the chroma line to designate a widescreen signal. Unfortunately, some switchers and amps throw away the DC component instead of passing it on to the TV.

Audio

Note: All DVD players have either a built-in Dolby Digital (AC-3) or MPEG audio decoder, or both. The decoder translates multi-channel audio into PCM audio. This is fed to the digital output and also converted to analog for standard audio output. Most players have only a 2-channel-output decoder, but some provide 6-channel output (details below).

• Digital audio (best): Almost all DVD players have digital audio outputs for Dolby Digital (AC-3), MPEG-2 audio, and PCM audio (including PCM from CDs). For DD or MPEG-2, the appropriate decoder is required in the receiver or as a separate audio processor. For PCM, a digital receiver or an outboard DAC is required. DTS is not yet available on DVDs; it will require new players and the appropriate decoder in the player or the receiver, or a separate audio processor. Some DVD players have coax connectors (SP/DIF), some have fiber-optic connectors (Toslink), and many have both. There are endless arguments over which of these is better. Coax seems to have more advocates, but suffice it to say that since the signal is digital, a quality cable of either type will provide similar results. Hook a 75-ohm coax cable or a fiber-optic cable between the player and the receiver/processor. (You might need a converter, see 3.1.) Some players provide separate connectors for DD/MPEG and PCM. On others, you may need to select the desired output format with the player setup menu or a switch on the back of the player.
  Note: Make sure you use an audio quality cable; a cheap RCA patch cable may cause the audio to not work.
  Note: Connecting to the AC-3/RF input will not work unless your reciever/decoder can autoswitch, since DVD digital audio is not in RF format (see below).
• Component analog audio (good): Some players provide 6-channel analog output from the internal Dolby Digital decoder. The digital-to-analog conversion quality may be better or worse than an external decoder. A receiver/amplifier with 6 inputs (or more than one amplifier) is required; this type of unit is often called "Dolby Digital ready" or "AC-3 ready." Unfortunately, in most cases you will be unable to adjust the volume of individual channels. Hook 6 audio cables to the RCA connectors on the player and to the matching connectors on the receiver/amplifier. Some receivers require an adapter cable with a DB-25 connector on one end and RCA connectors on the other.
• Stereo/surround analog audio (ok): All DVD players include two RCA connectors for stereo output. Any disc with Dolby Digital or MPEG-2 audio will automatically be decoded and downmixed to Dolby Surround output for connection to a regular stereo system or a Dolby Surround/Pro Logic system. Connect two audio cables between the player and a receiver, amplifier, or TV. Connectors may be labelled audio or left/right; left is usually white, right is usually red.
• RF digital audio (LD only): Combination LD/DVD players include AC-3 RF output for digital audio from laserdiscs. Hook a coax cable to the AC-3 RF input of the receiver/processor. Note: digital audio from DVDs does not come out of the RF output, it comes out of the optical/coax outputs. Analog audio from LDs will come out the stereo connectors, so three separate audio hookups are required to cover all variations.

[3.3] What are the sizes and capacities of DVD?

There are many variations on the DVD theme. There are two physical sizes: 12 cm (4.7 inches) and 8 cm (3.1 inches), both 1.2 mm thick. These are the same form factors as CD. A DVD disc can be single-sided or double-sided. Each side can have one or two layers of data. The amount of video a disc can hold depends on how much audio accompanies it and how heavily the video and audio are compressed. The oft-quoted figure of 133 minutes is apocryphal: a DVD with only one audio track easily holds over 160 minutes, and a single layer can actually hold up to 9 hours of video and audio if it's compressed to VHS quality.

At a rough average rate of 4.7 Mbps (3.5 Mbps for video, 1.2 Mbps for three 5.1-channel soundtracks), a single-layer DVD holds around 135 minutes. A two-hour movie with three soundtracks can average 5.2 Mbps. A dual-layer disc can hold a two-hour movie at an average of 9.5 Mbps (very close to the 10.08 Mbps limit).

------