Last week, Brian Felsen went over the planning stages of DVD production. This week, he clues us in on premastering.
The DVD is a digital storage media. Any content you have in analog format must be converted to the appropriate digital format. Many systems are designed to grab, or digitize, your video content with little loss of resolution; with improved processor speeds, video capture and editing can be handled on a modern Windows or Macintosh system. Inexpensive IEEE-1394 interface cards can bring in digital video content directly from your miniDV camcorder, and this interface is a standard feature on many computers. Professional applications, however, generally require more sophisticated tools that represent a complete hardware and software solution, such as the Avid Editing Suite. Similar software suites have the ability to conduct on and offline editing, and work for both PC and Macintosh. Some of these products are able to grab video from a magnetic source tape (High 8, Beta, VHS, etc.), convert it to digital format, and save it in a selected format. Common digital video formats include QuickTime movies, AVI, MPEG-1, MPEG-2, and MPEG-4.
DVD video is generally encoded in MPEG-2 format. MPEG-2 uses lossy compression that removes redundant and imperceptible information. At rates above 6 million bits/second, there is little perceptible difference between the encoded file and the original master. At average video data rates of 3.5 to 6 Mbps (million bits/second), compression artifacts (such as color banding, blurriness, blockiness, fuzzy dots, shimmering, or missing detail) may be occasionally noticeable. Even at lower data rates, most DVDs exhibit few MPEG compression artifacts. Your video grabbing or encoding software lets you set the compression ratios to be used (based on any of the popular compression algorithms). If your movie is longer than 130 minutes or if you are including many features and extras on your DVD, you may be faced with a tradeoff of having to increase compression (with a slight loss in video quality) or incurring the additional expense of replicating it onto a disc that holds more data than the DVD-5 (such as the DVD-9).
In order to digitally encode the video in MPEG format (and the audio into a format such as Dolby Digital), you must use authoring software. DVDs that take advantage of DVD-Video’s MPEG-2 video and multi-channel Dolby Digital or MPEG-2 audio require video and audio encoding. Simply putting MPEG files or AVI files on a disc will not make it compatible with all DVD players, as the audio and video signals have to be properly multiplexed so they play on a standalone unit. Video encoding tools include brands such as Canopus, Cinemacraft, Dazzle, DVDComposer, Wired MediaPress Pro, Sonic, and Apple Compressor; audio encoding tools also include Digital Vision, Dolby, and Sonic Foundry. Because technology is constantly changing, please check the internet for reviews of these and other authoring programs.
If you are encoding your own video, it is important to watch the bit-rate, as not all players can handle high constant bit-rate (CBR) sources. For maximum compatibility, your average bit-rate should probably be between 4,000-6,000 bps. If you are converting between PAL and NTSC, software tools such as Adobe After Effects and Canopus ProCoder do a good job at low cost. It is important to note that the creation of compressed video in MPEG-2 format can require considerable expertise to obtain satisfactory results. Whenever necessary, seek guidance or assistance for handling content conversion that may be beyond the capabilities of your computer system or experience.
OUTSOURCING THE TRANSFER
In many cases it is easier to achieve professional results by outsourcing the digital encoding process. Lab rates are relatively inexpensive, and many companies can encode the content with high-end decks and encoding tools from Sonic, Spruce, Apple, Wired, or Digital Vision. A good lab such as Disc Makers can help you with the transfer and encoding and will accept your finished video on any standard format, including BetaCam, Betacam SP, Betacam SX, Digital Betacam (DigiBeta), DVCAM, Mini-DV, MPEG IMX, QuickTime digital files, and VHS. The lab can take your footage and encode it into MPEG-2 format, providing the highest-quality video allowed by either constant bit-rate (CBR) or variable bit-rate (VBR) encoding.
-If you are outsourcing the encoding to a laboratory and are transferring from videotape, you should keep the following points in mind:
• -Try to send a tape that is as close to the master as possible. If it’s analog, the more generations away from the master tape you go, the more degradation will creep in.
• -Including color bars at the head of your tape is a must. This will help the lab properly calibrate the incoming signal.
• -We strongly suggest including a 1kHz reference tone at the head of your tape, usually during the color bars, which will help ensure a clean transfer of the soundtrack with no distortion.
If you are providing a lab with digital files, please be aware of the following:
-• -Many manufacturers require digital video files to be provided in QuickTime or AVI format. Files should be uncompressed or have compression set to the highest quality. It is usually best not to compress your files with a hardware codec, as many manufacturers cannot work from a file that relies on hardware compression.
-• -Most manufacturers require digital audio files to be provided in AIFF, WAV, or SDII format, with a sample rate of 48kHz and not 44.1kHz.
AUTHORING – design, layout and testing
Authoring is the process of taking your video project assets and combining them into a working DVD. It is more than just capturing or transferring the video and burning it – it involves designing and organizing the content for a DVD. If time is not a factor, DIY (do-it-yourself) authoring could be the most economical way to deliver a master for duplication or replication, but you must be prepared to learn everything necessary to create a suitable master; depending on the software and your level of expertise with computers, the learning curve can be fairly steep and time consuming.
There are many products that enable the producer to author his or her own DVD, including Apple’s DVD Studio Pro for Mac and ULead’s DVD Movie Factory for PC; there are other fine ones from Apple (iDVD), Adobe (Encore), Pinnacle (Impression DVD-Pro), and Sonic (DVDit!). Even entry level digital video editing tools often include sophisticated video transitions, audio effects, titling capabilities, and a variety of video output formats. Higher-end tools for broadcast production or professional DVD creation cost thousands rather than hundreds of dollars. Since competition is fierce in this segment of the software industry, it is important to keep up to date on new products and developments and to read software reviews at sites such as Digital Producer (www.digital producer.com) and Digital Video magazine (www.dv.com).
A well-designed interface can distinguish an exceptional DVD from a more pedestrian title. Most discs do not contain all features (menus with motion, alt-angle video streams, multiple audio/subtitle tracks, seamless branching, closed captions, subtitle tracks, slideshows, CSS/Macrovision, parental control, etc.) that a DVD could contain, and each feature must be specially authored. If you are designing the DVD interface using a powerful authoring tool, your options are wide open, so you need to have a strong idea of how the menu will work before you begin. A blueprint or “design document” can be an important tool for coordinating the effort. It is worth surveying some of the different DVD-Video titles on the market to get a sense of what is available. Make notes about those interface design approaches that seem most effective to you. The Web is a great place to pick up ideas and gain inspiration for your own projects; as an interface designer, you will need to stay in touch with trends and aesthetic principles being used by other designers and firms.
There are many issues to consider when authoring your own DVD.
MENU AND INTERFACE DESIGN
You may want to include a menu with chapter points, so the viewer can skip to the beginnings of certain scenes, chapter marks as specified by your timecode. DVD-Video content is broken into “titles” (movies or albums) and “parts of titles” (chapters or songs); titles are made up of “cells” grouped into “programs” and linked together by one or more “program chains” (PGC). In this way, menus allow the viewer to navigate through the DVD, enabling them to skip through the film; choose alternate audio tracks, subtitles, and camera angles; view a trailer; learn more about the film and filmmakers; and connect to the internet through web links.
A DVD-Video disc can have up to 8 audio tracks (streams) associated with each video track (or each video angle). Each audio track can be in one of three formats: PCM, Dolby Digital AC-3 (1 to 5.1 channels), or MPEG-2 audio (1 to 5.1 or 7.1 channels). Linear PCM is uncompressed digital audio, the same format used on CDs and most studio masters. MPEG audio is not often used on DVDs; although some inexpensive DVD recording software uses MPEG audio, this goes against the DVD standard and is not supported by all NTSC players. Dolby Digital is the format used for audio tracks on almost all NTSC DVDs; it supports multi-channel digital audio using lossy AC-3 coding technology from the original PCM source.
There are therefore many multi-channel surround sound encoding options for the digital video producer. Almost every DVD player in the world has an internal 2-channel Dolby Digital decoder which converts Dolby Digital into stereo audio that can be fed to almost any type of audio equipment as a standard analog stereo signal. Audio decoding technologies such as Dolby Surround, Dolby Pro Logic, and Dolby Pro Logic II enable the audio to be played on any stereo system or even a mono system. Dolby Digital encodes each channel independently and can carry up to 5 channels (left, center, right, left surround, right surround) plus an omnidirectional low-frequency channel. The built-in, 2-channel Dolby Digital decoder in every DVD player handles multichannel audio by downmixing it to two channels using Dolby Surround. This allows the analog stereo outputs to be connected to just about anything, including TVs and receivers with Dolby Pro Logic capability. Most DVD players also output the downmixed 2-channel Dolby Surround signal in digital PCM format, which can be connected to a digital audio receiver, most of which do Dolby Pro Logic decoding. The Dolby Digital Surround EX format (DD-EX) is more compatible than DTS, which some DVD players do not recognize at all. If incorporating surround sound into your DVD title, it is important to carefully research and test the compatibility of your output signal with existing players.
Another decision for the DVD producer to make is whether to include copy protection on the replicated disc. CPSA (content protection system architecture) is the name given to the overall framework for security and access control across the entire DVD family. These include analog systems such as Macrovision, “serial” copy protection (CGMS), and Content Scrambling System (CSS).Note: None of these copy-protection schemes will stop well-equipped pirates, and including them may add to the cost of replication. In addition, all DVD manufacturing plants require you to supply a DLT master in order to provide you with CSS or Macrovision.
Not only do you want to use test copies of a DVD title to ensure links and content are presented properly, but this can also be a valuable means of ensuring the playback performance of the title is adequate. Testing audio and video segments, animation, interactive sequences, etc., can help ensure program design is appropriate for the product. Poor performance suggests you may need to revise your design or reprocess some content, such as video material.
OUTSOURCING THE AUTHORING OF YOUR DVD PROJECT
Considering the time it takes to shoot and edit a film, it may not be worth your while to spend several additional weeks on the encoding, authoring, and formatting. The premastering, creation of a suitable interface, testing and review can take hundreds of hours of preparation time, not including self-education and trial-and-error. If your project includes complex elements, it may be worthwhile to consult with someone more experienced, particularly if you are producing your first DVD. Multimedia specialists such as those at Disc Makers can turn your video presentations into an interactive DVD with customized menu options and user-friendly navigation, and they can help you add the following elements to your DVD:
• Dolby Digital 5.1 Surround audio encoding
• Widescreen video encoding
• -Engaging Interfaces (such as full-motion, interactive menus; direct-access navigation to chapters and tracks; hidden “Easter Egg” features; and links to your Web site and online sales tools)
• Copyright protection systems
• Regional encoding
• Multiple audio tracks
• Commentary tracks
If you have any questions about the authoring process, or for pricing, call Disc Makers’ help line at 1-800-237-6666, or email email@example.com.
FORMATTING and preparing your master
The final step in premastering is to structure the files for the particular format and then to copy them to a distribution medium (such as DVD-R or another form of removable media). In addition to the encoding and authoring, there are six additional points to consider when preparing your master for duplication or replication.
1. -Use the UDF File Format. Whereas ISO-9660 works well as a universal cross-platform file structure for CDs, it also imposes certain constraints that make it difficult to use for rewritable media and that complicate multiplatform compatibility. The Universal Disc Format (UDF) on the other hand, was developed by the Optical Storage Technology Association to provide a more flexible, more resilient organizational system for disc storage that defines both the file system and volume structure. UDF has become the accepted standard for handling DVD files and volumes; when authoring and premastering DVDs and DVD-ROMs, it is essential that you use UDF to create your file and volume organization. Ahead Nero, Padus Disc Juggler, Gear Pro DVD, Roxio Toast Titanium and DVD Creator, and Sonic ROM Formatter are just a few DVD-ROM formatting tools that work with the UDF file system and bridge format. Whatever program you use, it is important to check that it also supports the Windows Joliet format, full equivalence between UDF and Joliet filenames, and all Mac OS file systems.
2. -Use Quality Media. The increasing popularity of DVDs has resulted in some marginal media suppliers introducing recordable discs of questionable quality. Don’t risk compromising the usability of your master by recording it on a disc of inferior quality. Bargain DVD-R discs sometimes contain bubbles in the polycarbonate, inconsistencies in the dye layer, and other imperfections that can cause problems when you attempt to make a glass master from the recorded DVD. High quality media can be found at many different outlets for a few dollars per disc. Stick to name brands, such as Sony, Fuji, and Disc Makers Ultra – available at www.discmarket.com – to avoid problems. The pennies per disc that you may save by going with a cheaper brand may cost you hundreds of dollars if your project is delayed because of problems creating the glass master. The standard format for submitting DVD material for replication is DVD-R (for DVD-5 and DVD-10), or DLTs with DDP files (required for DVD-9). You may use authoring or general grade DVD-R media. Most manufacturers, including Disc Makers, cannot accept DVD-RW, DVD+RW, or DVD-RAM for DVD replication or duplication. It is important to note that although Disc Makers accepts submissions on DVD-R, not all others do. There can be problems with compatibility and data loss when using DVD-R, so it is wise to generate a checksum that the replicator can use for verification purposes. Not all authoring software intended for DVD-R will support CSS, Macrovision, or region coding. These features require direct output to DLT. They are not supported by DVD-R general media.
3. -Make a Safety Copy of Your Master. It is extremely important that a safety copy be made of your master before you ship or deliver it anywhere. We’ve all had experiences with items that were damaged or lost during shipping and handling. Your master is the result of months of hard work and money spent – a safety copy is a small price to pay to preserve your irreplaceable images. Keep the secure copy in a safe place, and send out the original master to be mastered or manufactured.
4. -Do Not use Adhesive Labels. We recommend that you do not use adhesive labels on your masters. They can unbalance the disc and the adhesive may attack the recorded layers underneath. If you write on your master disc, use a felt-tip pen. Ball point pens or pencils will damage the disc.
5. -Handle Your Master Carefully. Handle all masters carefully, both before and after recording. Touch them only by the edges and keep them free of fingerprints and scratches that can cause data errors.
6. -Protect Your Rights. Any artwork you create is your property, but that can sometimes be difficult to prove in court. We strongly advise that you copyright your original material with the United States Copyright Office (www.copyright.gov, 202-707-9100), where you can also get information about registration, and the appropriate forms. Disc Makers participates in the International Recording Media Association (IRMA) Anti-Piracy Compliance Program, which protects property rights owners from the unauthorized distribution of their content. For compliance information, go to www.discmakers.com/irma.
Check back next week when Brian takes us into the manufacturing of your disc.
For more info on Disc Makers, visit the company’s website.