DVD: A technical note
Authored by Terry Cornall
What DVD is (trying to be)
Physical Disc Format
- A replacement for CD, CD-R, CDI, CD-Movie, CD-RW
- Delivery media for Digital Movies
- Delivery media for Digital Audio
- High capacity Read-Only data media
- High capacity Read/Write data media
- Same size as CD-ROM. 12 cm.
- Similar physical encoding to that used for CD-ROM, only denser
- Uses a shorter frequency laser. 650 nm
- Disc costs less than $1 to make, compared to about $3 for VHS tape.
This means that production companies may be able to release more movies
for sale whereas now the risks are too great and they prefer to use
rental as the income generator. Low production cost = more sell thru.
- DVD kit consists of a drive and an MPEG2 decoder card although s/w
MPEG2 decoders are avialable they need at least a 300 Mhz pentiumII
- There are two supported file structure types:
ISO 9660 which is the same as CD-ROMs and Micro UDF which is a
cross-platform standard for read and writeable data. Works on Unix, PCs
- Double-sided-double layered DVD has 26 times the capacity of a CDROM
- Also navigational data, different camera angles etc. Total of up to
10Mbit/s by DVD spec, typical 4Mbit/s fro the video, which is variable
- For raw read speed in data applications, the drives vary depending on
manufacturer and bus speeds. As an example, Creatives second generation
drive delivers up to 21 Mbits/s over EIDE bus. This isnÕt as fast as a
30x CDROM drive on ultrawide SCSSI which could do about 36 Mbits/s if the
PC could keep up with it.
|Name||Type of Application|
|DVD-Video||playback only Movie software - audio/visual packaged media|
|DVD-ROM||read only Large capacity data media. Great for multi-media|
|DVD-Audio||playback only Packaged media of high fidelity music|
|DVD-R||one-time recording high-capacity write-once computer use|
|DVD-RAM||rewriteable high-capacity rewriteable for computer use|
- From 2 hrs MPEG2 video (single-sided-single-layer) up to 8 hours (dsdl)
- MPEG2 audio-1 to 7.1 channels, Dolby-1 to 5.1 channels, PCM-1 to 8
channels (The .1 channel is a subwoofer)
- MPEG2 audio is compressed from 16 bit 48 ksps .Uses psychoacoustic
model to remove imperceptive sound and sub-band coding. i.e uses
quantisation in the frequency domain
- Dolby AC3 is compressed from 16 bit 48 ksps 5 channels surround-sound
at 20-20,000 hz + 1 bass at 20-120 hz
- PCM is: 16, 20 or 24 bits uncompressed sampled audio at up to 96 ksps.
(CD is 16 bit 44.1 ksps)
- Various screen formats supported inc 16:9 aspect ratio, pan and scan,
widescreen and letterbox
- Widescreen and letterbox are different. Letterbox is for viewing 16:9
aspect ratio video on a 4:3 aspect ratio monitor and widescreen is for
16:9 aspect ratio monitors.
- Zoom is not part of the DVD standard. Is an add on.
- Proposed to have various versions or ratings of the movie on the disk
and use the seamless branching to navigate through the scenes that
differ. This is also used to good advantage for interactive games.
- 32 subtitle/karaoke tracks. 9 camera angles
- Seamless branching of video for multiple story lines
- Rewind and fast forward with no delays
- File system is independent of operating system
- Not just a movie data file structure. Content and navigation data both included
- Menus and interactive navigation supported/built in
- At least hundreds of DVD movie titles available from the US and via
Internet distributers. At least 36 currently (April 98) available in
- Multiple security methods can be applied, but all are optional
- Region codes. One or many on disc. Only one on player. Protects defined
- Region codes can be bypassed or changed on many players (Invalidates
warranty on player)
- Macrovision 7 copy degradation prevents good quality copies from player
- Macrovision can be disabled on at least one player (Probably Invalidates warranty on player)
- Copy Generation Management System (CGMS) prevents copying with
equipment that uses CGMS. (May be more useful in future, in FireWire ISO1390 systems)
- Content Scramble System (CSS) is a key-based encryption method that
prevents playback on unauthorised equipment
- Divx is a Video format that uses triple DES encryption to restrict
access to the video.
- Divx is by Digital Video Extreme and the discs will be distributed by
Circuit City and The Good Guys!.
- Designed for throw-away movie hire
- Cheap disk purchase (<$5 US) but a limited playtime of 2 days. Has a
built-in modem because the player has to be able to go online for it to work.
- Can pay via online transaction for further viewing time ($3 us). Ca
purchase unlimited view time
- Charges usage to an account during off-peak phone time.
- Consumer is not charged for phone calls.
- Player will work offline for a limited period.
- Will play DVD discs
- May (probably already has) slow uptake of DVD technology
- Does have a sizable no of supporters, including Disney, 20th
Century-Fox, Times-Warner, MGM, Pioneer and JVC
- Manufacturers have agreed on DVD Forum spec for ROM
- Second generation DVD ROM drives are compatible with CD-ROM, CD-R, CDI,
DVD-Video and DVD-ROM
- Limited but growing number of software packages available (Mostly games)
10. AUDIO and RAM
- Sony and Phillips have split away from the DVD Forum again with Super
CD Audio discs
- A standard for audio-only DVD discs has not yet been finalised. Was
supposed to have been in sept 1997, now it looks like May 98 at earliest.
1999 for music DVDs?
- Conflict over DVD-RAM and DVD-rewritable standards. HP, Sony, Phillips,
Mitsubish, Ricoh are pushing a 3 G/layer standard that is different and
incompatible with the DVD ForumÕs DVD-RAM format. Their main objections
were about the need for a caddy, compatibility with DVD-ROM and capacity.
Most of these issues have been addressed by the DVD ForumÕs latest proposal
- NEC was pursuing a 5G format but has been lured back to the Forum by
their latest version which has 4.7G/layer.
DVD resource Forum
RobertÕs DVD page
Digital Video Express