Putting Content on Your Disc

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Now let's talk about the types of content you can use in your DVD productions.

What Audio and Video Formats Can I Use?

DVDs can contain video in MPEG-1 and MPEG-2 formats. Most authoring programs can input a wide variety of video formats, such as MPEG, AVI, and MOV, and convert to MPEG-1 or 2 as necessary before burning the disc.

In terms of audio, DVDs can contain an uncompressed LPCM (linear pulse code modulated, same as CD-Audio) format as well as Dolby Digital (also known as AC-3) and MPEG-2 audio compression.

Why Should I Care About Dolby Digital Audio?

In the United States, DVD players are not required to play back MPEG-2 audio compression, just LPCM and AC-3. While most newer DVD players can play discs with MPEG-2 audio, there's a risk that older players won't be able to decode the audio. For this reason, few if any Hollywood DVDs ship solely with MPEG-2 audio compression; they all use Dolby Digital.

If you're producing for business use, Dolby is the only viable audio compression option, though not all authoring products can output Dolby audio streams. If your authoring program doesn't support Dolby, you're at a significant disadvantage quality-wise, even if disk capacity isn't an issue. Here's why.

If you're starting with DV video, your uncompressed audio data rate may be as high as 1,500Kbps. To achieve the optimal 8Mbps bitrate for the mixed audio/video stream, you'll have to encode the video at 6,500Kbps. In contrast, with Dolby you can produce a high-quality compressed audio stream at around 200Kbps, leaving 7,800 for video, which is 20 percent higher than the maximum bitrate with PCM audio. With high-motion video, the higher bitrate could produce noticeably better quality.

The difference gets even more significant as you store more video minutes on the DVD. With two hours of video to store on a 4.7GB disc, the producer using Dolby Digital audio can encode the video to about 4,700Kbps, a challenging rate, but probably acceptable for lower-motion video. Without Dolby, however, the producer must encode to 3,300Kbps, at which point it starts to look pretty awful.

You can see why then using Dolby Digital audio is a critical feature for anyone producing DVDs for professional use.

Can I Insert Slideshows?

Yes. You can combine digital pictures and audio, and many DVD authoring programs provide dedicated slideshow creation interfaces. How the program renders the slideshow has a dramatic impact on slideshow bitrate and file size.

Some programs convert the slideshow to a video at 30 frames per second, and encode it just like any other video file. If each image in the slideshow displays for five seconds, and your average video bit rate is 7Mbps, each slide will consume 35 megabits of data (7Mbps times 5 seconds) or close to 4.4 megabytes of space on the disc.

Other programs create "true" DVD slideshows that instruct the player to display a single frame for the entire duration specified in the slideshow. Since a single frame of video might only be about 60 kilobytes in size, five seconds of video consumes 60 kilobytes on the disc. Also, if you take this approach, or avoid the compression artifacts that often accompany still images encoded into MPEG-2 format, and achieve a more crisp display.

If your productions are slideshow-intensive, and require precise bit-budgeting, find out which of the above methods your authoring program uses; otherwise your calculations will be off. If the manual or product FAQ doesn't provide the answer, build and render a 10-minute slideshow to DVD and see how much space it consumes.

Many video and DVD tools are now incorporating basic "pan and zoom" capabilities for spicing up slideshows with motion effects think of how Ken Burns uses this technique in his documentaries. With "true" DVD slideshows, involving only MPEG-2 (I-Frame) stills, the only place you can add effects is during transitions. So if you want to pan and zoom your images, converting the slideshow to a video is your only option.

What About Text Subtitles?

The DVD specification supports up to 32 text tracks for karaoke and subtitling. But not all DVD authoring programs can insert text subtitles. See Chapter 11 for more on subtitles.

What About Multiple Audio Tracks?

The DVD specification supports up to eight tracks of digital audio, encoded in PCM, AC-3, or MPEG-2. Again, not all DVD authoring programs can insert multiple audio tracks.

By the Way, What's a VOB File?

VOB stands for Video Object. After rendering all your audio and video files into their required formats, your authoring program creates one or more VOB file, which also contain the menus along with the content. Essentially, it's your MPEG-2 video plus all the descriptive and navigational information that makes your content DVD-compatible. These are the files that are actually burned to disc.

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    DV 101. A Hands-On Guide for Business, Government & Educators
    DV 101: A Hands-On Guide for Business, Government and Educators
    ISBN: 0321348974
    EAN: 2147483647
    Year: 2005
    Pages: 110
    Authors: Jan Ozer

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