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Chapter 4. Video & Audio Overview: Essen... > File Formats, Transcoding, and Other...

File Formats, Transcoding, and Other Tidbits

As a DVD designer/producer, your ultimate goal is to create content that is in a DVD--compatible format.

Video format for DVD

The official DVD specification requires video to be in the MPEG-2 format. MPEG (Motion Picture Experts Group) is a digital video compression standard that dramatically reduces the size of digital video files while retaining very high quality.

DVDs will accept MPEG-1 formated video, but MPEG-1 is much lower quality and optimized for smaller picture sizes rather than full-size movies.

Transcoding and encoding


Since all NLE (Nonlinear Editor) applications need to perform the same kinds of editing tasks, they all provide many of the same features and tools, but packaged and organized in their own ways.

A partial list of features you should expect to find in a robust NLE can be found on page 64.

Entry-level NLE vendors omit many of these features so they can provide a less complex and more affordable version of their products.

Most nonlinear editing applications (often referred to as NLE applications) that you'll use to edit digital video and audio can export video as MPEG-2 files, ready to use in a DVD authoring application.

NLEs that do not export video in the MPEG-2 format can export or save in other formats that you can then transcode (change from one format to another) to the MPEG-2 format; you'll use encoding hardware or software to do this. Many entry-level DVD authoring programs, such as DVDit! and iDVD, do this automatically when you import files.

There are many encoders available. Software encoders, although not as fast as hardware encoders, offer a very attractive combination of affordability, convenience, and quality. Technology leaders such as Apple, Discreet, Media 100, and Sonic Solutions offer popular encoders that can either work as plug-ins you can access from your favorite editing program or use as stand-alone applications.

Even when video editing software can export projects in the MPEG-2 format, some DVD designers prefer to use a favorite third-party encoder rather than the one built into the software. Experienced professionals may use certain encoders for different types of video, since some encoding software may favor speed over quality, or may be better at compressing certain kinds of scenes, such as video that contains a lot of fast motion. Software encoders all use their own algorithms to define the encoding procedure, so results may vary dramatically if you encode the same video with different encoders.

QuickTime Pro is a versatile software encoder that can open different kinds of audio and video files, then transcode them to a large variety of other formats.

Apple's QuickTime application is best known as a free, cross-platform player for multimedia files, but it's also a very powerful transcoder when you upgrade to the QuickTime Pro version (about $30). Many NLEs can export or save projects in the QuickTime format. The example on the previous page shows a video sequence that we edited in an NLE, then opened in QuickTime to export and transcode to the DVD-compatible MPEG-2 format.

BitVice, shown above, is a stand-alone encoder with which you encode DV files into the MPEG-2 format. Software such as this lets you encode video efficiently with a technology known as VBR (Variable Bit Rate). VBR compares data information between frames and makes compression decisions that vary from frame to frame. The small preview window in the upper-left corner will show the video stepping forward and back as the software compares frames.

Digital video format


MPEG-2 is a video-only format. When you encode a movie as MPEG-2, the audio part of the movie is extracted and saved as a separate audio file. The two files are synced back together when you import them into your DVD authoring software.

When you import video from a camcorder into your computer, it's saved in a DV (Digital Video) format.

On a Macintosh, the DV format is handled by QuickTime and the imported video clips are QuickTime files.

On a PC, imported video files are saved as Windows Media Files or AVI files. Some Windows-based NLEs prefer to use a file format called AVI (Audio Video Interleaved), a Microsoft sound and motion picture file format. Any number of encoders, including QuickTime, can transcode AVI-formatted files into the MPEG-2 format.

Audio formats

DVD specifications also have specific requirements for audio files. Audio must be either Dolby AC-3 format or a Linear PCM format, which includes both WAV and AIFF files. WAV is a standard PC audio format developed by Microsoft, and AIFF (Audio Interchange File Format) is a Macintosh format. Your NLE software (Adobe Premiere, Final Cut Pro, etc.) can export audio in the required formats.

Video standards

When you create a new project in a digital video editing application, you must choose a video standard for the project. There are three different video standards used around the world: NTSC, PAL, and SECAM. NTSC is the video standard in North America and Japan; PAL is the standard in Europe and Australia; and SECAM is the standard in France, countries of the former Soviet Union, and certain other countries.

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