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Bit budgeting
About bit budgeting
Bit budgeting, or estimating the amount of space your project will occupy on DVD, is an important part of planning.
Bit budgeting helps you strike a balance between the quantity and quality of content and determine the optimal video
data rate. If your DVD includes minimal amounts of content, you can encode that content at a higher data rate
(which translates to higher quality) to take advantage of all available space on the DVD. Conversely, if your project
contains a large amount of content, you need to use a lower data rate (which translates to lower quality) to squeeze
it all onto the DVD.
Adobe Encore DVD automatically tracks bit budgeting during the authoring process. For small projects with limited
content, simply checking the amount of available space on the Disc panel during the authoring process is usually
sufficient to track your space usage. For large, complex projects, though, bit budgeting becomes much more
important to the authoring process, providing a check against the actual data rates achieved.
Generally, for projects with less than two hours of video, you can skip bit budgeting and let Adobe Encore DVD set
the data rate automatically.
To calculate a bit budget
Bit budgeting provides a target video data rate for the project. You can either use a pencil and paper to quickly
develop one, or you can create a spreadsheet to do the calculations for you.
When bit budgeting for projects to be distributed on 4.7 GB DVDs that contain a single stream of compressed audio,
you can use the simplified formula of 560 / x = bit rate in Mbps, where "x" represents minutes of video.
Calculate the total disc space available for the entire project.
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Calculate the disc space available for video. You achieve this by calculating the space required for audio, slide
shows, subtitles, and motion menus (other types of content are negligible in terms of bit budgeting), and subtracting
that amount from the total disc space. For more information, see "Average asset size" on page 27.
Note: If you include ROM content, make sure to include it in the space calculation.(See "To add ROM data to a DVD"
on page 191.)
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Calculate the target data rate of the video. You determine this by dividing the amount of space available for video
by the amount of video in the project.
Determine the maximum video bit rate by subtracting the combined audio and subtitle rate from the DVD data
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rate limit of 9.8 Mbps. (For example, if your combined audio and subtitle rate is 3.0 Mpbs, subtracting that from 9.8
Mpbs gives you a video rate of 6.8 Mbps.) Your goal is to determine the highest possible target video data rate within
the DVD data rate limit. If your target data rate is below 6 Mbps, consider using Variable Bit Rate (VBR) encoding.
When you use VBR encoding, you specify the maximum video data rate. (The average data rate is the target, but the
maximum rate provides some flexibility when encoding.)
Note: Keep your calculations simple by working with megabits (Mbits) and not megabytes (MB) when bit budgeting.
Mbps denotes Megabits per second. Also, hard disk capacity is typically calculated as a power of 2 (1 Kb = 2^10 bytes =
1024 bytes) while optical disc (DVD) capacity is labeled as a power of 0 (1 Kb = 10^3 bytes = 1,000 bytes). Use the power-
of-10 scheme for bit budgeting. The following conversion factors will aid in the calculations: 1 GB = 10^9 bytes =
1,000,000,000 bytes = 8,000,000,000 bits; 1,000,000 bits = 1 Megabit.
ADOBE ENCORE DVD 2.0
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