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Editor’s note: The following tip on bit budgeting for the web in DVD Studio Pro 4 is excerpted from Apple Pro Training Series: DVD Studio Pro 4, Second Edition by Martin Sitter and Adrian Ramseier with JemSchofield, published by Peachpit Press. Bit Budgeting From: Authoring Professional DVDs in Final Cut Studio 2; pgs. 392-394

Bit budgeting gets its name from the smallest unit of measurement in the digital world: a bit. A bit has a value of either 1 or 0 in the digital binary system. Bits are measured in units of thousand, million, billion, or trillion bytes. A byte is really just a packet of 8 bits, and both bits and bytes are units of measurement. Bits are usually used to measure speed (for example, 56 kilobit per second modem), whereas bytes are usually used to measure size (for example, 120 gigabyte hard drive). When abbreviated, measurements of bits use lowercase letters, and measurements of bytes use uppercase letters, as in Kbps (kilobits per second) versus MB (megabytes). The goal of bit budgeting is to encode your video and audio assets at the higest possible quality, while keeping the combines file sizes of your assets under the total disc capacity. Figuring out the maximum bit rate with which you can encode your files without making them too large to fit on the DVD is where the “budgeting” part of bit budgeting comes in. It is often helpful to use but budgeting equations or special calculators to estimate the size of a DVD project. We’ve included one calculator for you to experiment with on the book’s companion DVD, as Appendix B. These formulas can assist you in choosing a but rate for your media, so that it fits easily on a disc. For example, if you have video that is 2 hours long, a very high bit rate – such as 8 megabits per second (Mbps) – might make the resulting MPEG-2 file too large for a 4.7 GB DVD-5 disc, particularly after other assets, such as audio, subtitles, slideshows, and so on, are added into the equation. Compressor enables you to control the file size of your final project. There is a little bit of math involved, but don’t worry, you will learn a few tricks that will make it easy to calculate the estimated disc size. But do take bit budgeting seriously. Even experienced authors are sometimes forced to re-encode asset files if they don’t properly budget their projects, especially when encoding feature-length materials. What if the Data Doesn’t Fit? If all of your assets will not fit on the DVD, you have a number of options:

• Encode your audio to Dolby Digital AC-3 files. This is almost required for programs longer than 90 minutes. If you encode a two-hour movie, the available bit rate for the video is a mere 3.4 Mbps. Using Dolby Digital audio encoding, you can still encode your video at 4.7 Mbps. Why do you save this much space? PCM, although high in quality, is the least efficient file format in the DVD-Video specification. PCM audio files consume 1.5 Mbps of the total bandwidth for playback. However, encoding audio files using Dolby Digital at 192 Kbps frees an additional 1.3 Mbps for your video bit rate.

• Use stories rather than duplicating media. Since stories allow you to perform relatively seamless branching, you can combine several versions of the same program on a disc by reusing media. However, viewers may notice a brief pause when the jump occurs.

• Leave assets off the disc. This works only if you are not required to use all elements in your project.

Author a DVD-9, which will give you a total disc capacity of 7.95 GB. Measuring Disc Size The DVD Studio Pro toolbar includes a Disc Meter indicator to measure how much space your assets occupy. The problem with using this indicator to monitor progress is that by the time the assets are in your project, they’re already encoded. Unless you want to spend time re-encoding video (and you probably don’t), you’ll need to calculate the combined file sizes of all audio and video assets – including motion menu background, audio for slideshows, and all alternate audio and video streams – before adding them to your project. Using Bit Budgeting Methods An easy bit budgeting method is to calculate a bit rate for your video using the formula 560 divided by x, where x is the length in minutes of your video assets. This formula assumes that you are using compressed audio, such as AC-3. If you are using PCM audio, you need to subtract another 1.3 Mbps from the result of this equation. For example, if you have 120 minutes of video, you get an approximate bit rate of 4.67 Mbps (560 divided by 120 = 4.67). If you are using the AIFF uncompressed audio that the QuickTime encoder supplies, your available bit rate for your video will be 3.37 Mbps. TIP: Do not forget that this bit rate is the combined bit rate for audio and video, so you will have to split it between the audio and video streams. If you are using multiple audio and video streams, you can also use a bit budget calculator, which is usually a simple spreadsheet that helps you calculate the bit rate for your video and audio assets. See Appendix B for the information about a bit budget calculator.

Excerpted from Apple Pro Training Series: DVD Studio Pro 4, Second Edition by Martin Sitter and Adrian Ramseier with Jem Schofield. Copyright © 2008. Used with permission of Pearson Education, Inc. and Peachpit Press.