How Do I Fit All This on Disc?

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Good question, if not the question. Unfortunately, getting all your content to fit on disc is often harder than you think, and certainly harder than it needs to be.

Let's quickly review. You've added menus, audio, video, and slideshows to your disc. If your authoring software gives you a Dolby audio compression option, you'll almost certainly use it, so that data rate is fixed. This leaves the data rate of the video as the most significant variable you need to adjust to fit the contents on disc.

Some programs figure out the required video data rate internally, and automatically compress the video to the bitrate necessary to fit it all on disc. Obviously, this is the preferred approach. Other programs, however, force you to calculate the necessary rate, though, generally, not without some assistance.

Specifically, when starting a project, you'll usually set the project encoding parameters, using a control such as that shown in Figure 8.10. Then, as you add content to the project, you'll see the contents accumulate in some kind of meter, such as the one shown in Figure 8.11.

Figure 8.10. Setting project encoding parameters.


Figure 8.11. A capacity meter that tells you how much room remains (on the left), or when you're out of space (on the right).


If you exceed the capacity of the disc, you have two choices: lower the video bitrate or delete content. This type of scrambling occurs more often than you think, and why I recommend encoding all assets as part of the final rendering and burning process.

Specifically, if you're working with a separate video editor and authoring program, don't encode into MPEG-2 format when outputting from the editor, because you may later discover that the bitrate was too high or too low. Rather, output in DV format and encode as part of the final rendering process.

Similarly, some authoring programs let you encode video files into MPEG-2 format as an interim production step. Unless your disc contents are absolutely nailed down, however, you may find yourself having to encode again to a different bitrate. Again, I can't, recommend enough waiting until the project is finished, and the optimal bitrate conclusive, before you encode your video.

What About Bit Budgeting?

Bit budgeting is for Type A personalities who want to know how much video will fit on their discs and at what rate before they start authoring. Not a bad thing (hey, I'm definitely Type A), but a bit difficult to explain in the abstract, because bit-budgeting is both project- and authoring program-specific. Let's review some general principles.

The first principle is that all content counts. It's not just video, audio, and slideshows; it's all of that plus audio menus, video menus, animated button frames, multiple audio tracks for languages, and multiple subtitle tracks. To perform a precise bit-budget allocation, you need to know the following:

  • The bitrate used for audio menus (generally the bitrate applied to other audio files).

  • The bitrate the program uses for video menus (generally, the bitrate applied to video files).

  • How the program encodes slideshows (whether it converts the slideshow into a video file or displays the still images).

  • The bitrate used for language tracks (generally, the bitrate applied to other audio files).

The second principle is that authoring programs typically can't use the same asset multiple times. For example, suppose you have four menus in your project and use the same two-minute video behind each menu. In a perfect world, the authoring program would encode and store the video once on disc and tell the DVD player to play that file behind each menu. Unfortunately, most authoring programs don't work that way; they produce the video file four times and store all four files on the disc.

Sounds Too Complex; How About Some Examples?

Sounds good to me. Table 8.2 shows the bitrate for five projects, ranging in size from 60 minutes to 120 minutes. Included are encoding parameters for programs both with Dolby encoding (at 192Kbps) and with LPCM output (at 44.1kHz, 16-bit stereo, or 1,408Kbps).

Table 8.2. Video-only bitrates for five project sizes using Dolby and PCM encoding.

Disc capacity

4.7GB

4.7GB

4.7GB

4.7GB

4.7GB

Minutes of video

120

105

90

75

60

Video-only bitrate (Dolby)

4700

5400

6400

7700

7808

Video-only bitrate (LPCM)

3500

4200

5200

6500

6592


Let me add a couple of explanatory notes. First, the combined audio/video bitrate on any project burned to a DVD-Recordable disc should never exceed 8Mbps, and I've limited the video bitrates for both 60-minute projects to reflect this. Put another way; if your project has less than 60 minutes of video, bit budgeting isn't really an issue.

Second, if you're using MPEG-2 audio compression at a similar 192Kbps rate, the results will obviously be the same as those shown in Table 8.2. That said, I don't recommend using MPEG-2 audio for discs built for business use because of the compatibility issues I've already described.

Third, these numbers assume only one audio track and no audio or video menus. If you are including these in your project, you'll have to factor this content into the equation.

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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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