DVD Technology

DVD has become the most successful consumer electronics product of all time. DVD is vastly superior to consumer videotape and laserdisc. DVD manufacturing comprises premastering, glass mastering, replication, printing and packaging

Premastering

DVD-Video Premastering (sometimes referred to as authoring) services include:
  • Video Encoding.
  • Audio Encoding.
  • DVD-Video Authoring including adding menus, interactivity, subtitles etc.
  • Formatting DVD-Video and transfer to DLT tape for glass mastering.
  • DVD-R recording for testing and one-off production.

Preparing contents and making decisions about the DVD project are the first steps before creating a DVD. Changes are quite possible though rather difficult once the process starts, so proper preparation saves time, nerves and money. All assets should be prepared in the required format.

Video encoding

Video signal that will be on your DVD is digitized from a DigiBeta or BetaSp tape. Without using some form of data compression the DVD disc could only hold about three minutes of broadcast quality video, so DVD uses data compression standard to fit a complete movie onto a single side of a disc. Typically, the format is MPEG-2. It compresses the video data by up to 40:1 whilst still retaining very high picture quality. MPEG-2 Video is either encoded using a constant bit rate (CBR) or a variable bit rate (VBR). CBR encoding is optimal for shorter program lengths. VBR is the best choice for program lengths over 1 hour where exceptional quality compression is expected.

Audio encoding

Audio encoding can start from a number of different input sources. DA-88 time code DAT, DigiBeta, and BetaSP are all acceptable input sources. DVD Audio currently uses one of two audio compression formats, Dolby Digital AC-3 Surround Sound™ PCM or MPEG-2 multi-channel audio, to place one or more high quality multi-channel soundtracks alongside the video information.

Authoring

Authoring is the process of assembling various media assets (e.g. video, audio, menus, screens, multiple language subtitles, etc.) and programming the interactivity and relationships of those elements. Additionally, general DVD parameters such as parental control, copy protection, regional coding, are set to output specifications.

Multiplexing and Disc Imaging

Multiplexing is the stage when the assets, which have been authored, are combined into video objects (VOBs) and information files (IFO files), the building blocks of DVD-Video disc. After Multiplexing, the newly created VOB, IFO and other files are formatted into a final disc image, data package of a DVD-Video.

Outputting

The disc image can be outputted to a DVD-R or a DLT (Digital Linear Tape). DLT is the standard format from which replicators manufacture DVDs. Often a DVD-R is made along with a DLT for use as a check disc.

Glass mastering

From a DLT, replicators can mass produce DVD's. The DVD parameters that have been set during the authoring process are now implemented.

Replication (including mastering) is usually done by a large plant. A variety of machines are used to:
  • create a glass master,
  • create metal stamping masters,
  • stamp substrates in hydraulic molds,
  • apply reflective layers,
  • bond substrates together,
  • print labels, and insert discs in packages.

The first stage in the mastering process is the creation of a glass substrate. Glass is cleaned and polished to remove any surface anomalies.

In-Line Mastering

The glass substrate is loaded into the in-line mastering machine. The machine performs a thorough mechanical cleaning, then dispenses a photoresist coating onto the surface of the substrate. The glass is now ready for recording.

Master Recording

The glass master goes to the laser beam recorder. The formatted DLT tape is used as source material for the laser beam that records information onto the surface of the photoresist. The recording machine creates exposed areas in the surface of the photoresist coating. This results in a layer of digitally recorded information. Rinsing the glass master with a developing solution removes all those areas of the film that have been exposed to the laser light. What's left is a series of digitally encoded pits in the surface of the photoresist. Then comes the turn of the sputtering machine used to deposit a thin film of nickel coating onto the surface of the master.

Stamper Creation

The nickel-coated master is put into a plating bath. A process called electroforming allows a thin layer of electrolytic nickel to adhere to the surface of the master. The layer of nickel is then separated from the surface of the master. This layer of nickel is called a stamper. After being measured, trimmed and polished, the stamper is ready for replication process.

Most replication plants offer "one-off" or "check disc" services, where one to dozens of discs are made for testing before mass replication. Sometimes mastering may include an additional step for CSS encryption, Macrovision, and regionalization.

For projects requiring less than 50 copies, it can be cheaper to use DVD-R. Automated machines can feed DVD-R blanks into a recorder, and even print labels on each disc. This is called duplication, as distinguished from replication.

Some manufacturers provide duplication service when a project requires a small quantity of copies.

Replication

The stamper is then installed in the DVD molding machine. A DVD disc consists of two polycarbonate substrates bonded together. To create each substrate, molten polycarbonate resin is injected into the DVD molds and compressed against the stamper. The resin replicates the layer bumps. The molded substrates are now an exact copy of the original master. After molding, the substrates are then metalized with a reflective metal coating deposited onto the encoded surface of the substrate.

In the case of single-sided, single layer DVD 5 discs, the aluminum metalized substrate is bonded to an additional blank substrate as the top layer. For single-sided, dual-layer DVD 9 discs, a semi-reflective substrate is bonded to a fully reflective aluminum substrate on the top. For double-sided , single layer DVD 10 discs, two metalized layers are created and bonded.

DVD-5 (single sided, single layer, 4.7Gb)


DVD-9 (single sided, dual layer, 8.5Gb)


DVD-10 (double sided, single layer, 9.4Gb)


DVD-18 (double sided, dual layer, 17.0Gb)