Making Sure Your Content Will Fit

Be sure to allow time in the planning process to determine whether all of your assets will fit on the type of DVD you are using. You don’t want to be surprised when you are finished authoring the title—that is a bad time to find out that the assets won’t fit.

What Do You Mean a 4.7 GB DVD Won’t Hold 4.7 Gigabytes?

With computers, memory and disk size are commonly expressed in terms such as kilobyte, megabyte, and gigabyte. Technically, a kilobyte should represent 1000 bytes, but due to the binary numbering system computers use, a kilobyte actually represents 1024 bytes. Similarly, a megabyte represents 1,048,576 bytes (and not 1,000,000 bytes) and a gigabyte represents 1,073,741,824 bytes (and not 1,000,000,000 bytes).

Unfortunately, with DVD discs the terms megabyte and gigabyte do not use the same binary-based standard; they literally refer to the technically accurate 1,000,000 bytes for a megabyte and 1,000,000,000 bytes for a gigabyte. This means that a 4.7 GB DVD disc will actually hold only 4.37 binary-based gigabytes. While the difference is not large (relatively speaking), it must be accounted for if you intend to come close to filling the disc.

Important: When displaying estimated sizes, DVD Studio Pro uses the “1000 bytes equals a kilobyte” system. This means that the estimated sizes refer to the amount of space they will require on the DVD and will be a bit larger than the file sizes shown in the Finder. While the Finder shows binary-based file sizes, you can use its File > Get Info command to see both the binary-based file size and, in parentheses, the “1000 bytes equals a kilobyte” size.

Disc Options

You have a variety of DVD discs to choose from. The one you choose depends on your content, your budget, and whether you intend to use a DVD replication facility. DVD sizes are typically referred to with names such as DVD-5 and DVD-9. While the number in the name is intended to provide general guidance as to the capacity of the disc, it should not be relied on too strictly. (Note that a DVD-4 disc has a higher capacity than a DVD-5 disc.) The following tables list the common sizes used.

Red Laser Discs

The following table lists the names for discs based on red lasers.

DVD name
Disc size
Type
Capacity
DVD-1
8 cm
Single-sided, single-layer
1.46 GB (1.36 binary gigabytes)
DVD-2
8 cm
Single-sided, dual-layer
2.66 GB (2.47 binary gigabytes)
DVD-3
8 cm
Dual-sided, both sides single-layer
2.92 GB (2.72 binary gigabytes)
DVD-4
8 cm
Dual-sided, both sides dual-layer
5.32 GB (4.95 binary gigabytes)
DVD-5
12 cm
Single-sided, single-layer
4.7 GB (4.38 binary gigabytes)
DVD-9
12 cm
Single-sided, dual-layer
8.54 GB (7.95 binary gigabytes)
DVD-10
12 cm
Dual-sided, both sides single-layer
9.4 GB (8.75 binary gigabytes)
DVD-14
12 cm
Dual-sided, one side dual-layer
13.24 GB (12.32 binary gigabytes)
DVD-18
12 cm
Dual-sided, both sides dual-layer
17.08 GB (15.9 binary gigabytes)

If you intend to burn your own discs using your system’s DVD burner, you can only use DVD-5 and DVD-9 discs. To use any of the other sizes, you must use a DVD replication facility.

Blue Laser Discs

The following table lists the names for discs based on blue lasers.

DVD name
Disc size
Type
Capacity
HD DVD-4
8 cm
Single-sided, single-layer
4.5 GB (4.19 binary gigabytes)
HD DVD-9
8 cm
Single-sided, dual-layer
9.0 GB (8.38 binary gigabytes)
HD DVD-15
12 cm
Single-sided, single-layer
15.0 GB (13.97 binary gigabytes)
HD DVD-30
12 cm
Single-sided, dual-layer
30.0 GB (27.94 binary gigabytes)

Estimating Whether Your Content Will Fit

While you will often hear that a DVD-5 (or a 4.7 GB disc) can hold two hours of video content, this is really only a rough guideline. The actual amount of video a DVD-5 disc can hold depends on the bit rate the video is encoded at. Often overlooked is the size of audio files—if you plan to use uncompressed AIFF (PCM) audio, you must also take the additional space requirements into account when calculating whether all your content will fit.

If your project needs to fit on a DVD-5 disc that you can burn on your SuperDrive, you need to choose an appropriate bit rate. There is a simple formula you can use. See Fitting Your Project on a DVD-5 Disc for more information.

If you are flexible as to the DVD disc type you can use, you can experiment with different bit rates and determine the disc space required by each. This process is more detailed and includes more variables, such as taking into account additional audio streams and DVD-ROM content. See Calculating Disc Space Requirements for details on precisely determining your disc space requirements.

Fitting Your Project on a DVD-5 Disc

You can use this simple formula to estimate the bit rate you should use to fit your video on a DVD-5 disc:

560/x = bit rate

The “x” represents the length of the video (in minutes) and the resulting bit rate is in megabits per second (Mbps). This formula assumes you are using compressed audio, such as AC-3. If you are using uncompressed audio, you need to subtract 1.5 Mbps (assuming you are using 16-bit stereo at a 48 kHz sample rate) from the bit rate value.

For example, if you have 120 minutes of video, you get a suggested bit rate of 4.67 Mbps (560/120 = 4.67). If you are using uncompressed audio (such as the AIFF format the embedded AIFF encoder supplies), you need to reduce the bit rate to 3.17 Mbps to ensure the video and audio will fit on the disc.

Beware of Setting Your Bit Rate Too High

You will find that with some DVD projects, the content easily fits on the disc, and you may be tempted to use the highest video bit rate available. While higher bit rates produce better quality, you must take into account other factors before deciding to use the maximum allowable value.

The maximum video bit rate allowed on SD-based DVDs is 9.8 Mbps, but rarely is that practical to use because DVD players support combined video, audio, and subtitle bit rates of up to 10.08 Mbps. For HD-based DVDs, the maximum video bit rate is 29.4 Mbps for HD assets and 15.0 Mbps for any SD assets used in an HD project, with an overall maximum bit rate of 30.24 Mbps.

In practice, you should be conservative when determining how high of a bit rate to allow for. Trying to squeeze out the highest possible bit rate for your project can lead to player compatibility and disc space issues.A general recommendation is to not exceed 9.2 Mbps for the combined video and audio bit rates when authoring SD projects or 29 Mbps when authoring HD projects.

Important: If you are building your project and DVD Studio Pro detects that the bit rate of the multiplexed stream is too high, the build stops and an error message appears.

Using PCM or AC-3 Audio

A single PCM audio stream using typical settings (as produced with the embedded AIFF encoder) requires 1.536 Mbps, which leaves an absolute maximum bit rate for the video in an SD project of around 8.54 Mbps. If there are two PCM audio streams, 3.07 Mbps must be allowed for the audio, leaving just 7.01 Mbps for the video.

Note: Even though you can only play one audio stream at a time, the bit rates of all audio streams must be added together when determining the overall bit rate for a track. Similarly, all subtitle streams must be added together and added to the overall bit rate.

Using AC-3 audio in place of the PCM audio leaves far more room for the video bit rate. Stereo AC-3 audio using typical settings requires only about 224 kbps—using two stereo AC-3 streams in place of the PCM audio leaves about 9.6 Mbps for the video.

See Calculating a Project’s Disc Space Requirements for more information about allowances for other audio formats.

Subtitle Allowances

Subtitles generally use a very small bit rate—about 10 kbps per stream. Larger subtitles that change frequently or use graphics can have a significant impact though and can affect the maximum bit rate you can use for the video.

Multiple Video Angles

Using multiple video angles in a track also affects the maximum allowable video bit rate you can use. Due to the way the DVD specification requires video streams to be multiplexed together, the number of video streams determines the maximum video bit rate you can use in SD projects. The maximum combined bit rates (highest bit rate video stream + all audio streams + all subtitle streams) you can use for each multi- and mixed-angle track in an SD project is from 8.0 Mbps with two streams to 7.0 Mbps with nine streams. See Encoding Video for Multi-Angle Tracks for more information.

HD projects using multiple video angles in a track are limited to 24.0 Mbps for the maximum combined bit rates, regardless of the number of video angles.

Transitions

When you add a transition to a menu, to a still clip in a track, or to slides in a slideshow, you need to account for the additional video it creates.

  • In the case of menus, the transitions become short rendered video clips stored in the same video object (VOB) file as the menus. This means that, in addition to the overall amount of disc space menu transitions require, you must also consider their impact on the 1 GB menu VOB file size limit. See Standard SD DVD Video Zone Files for more information. You must also take into account that a transition video clip is rendered for each menu button that has transitions enabled—a menu with 18 buttons can require 18 transition video clips.

  • In the case of still clips in a track and slides in a slideshow, adding transitions increases the amount of disc space each requires even if the transition does not increase the length of the track or slideshow. This is because stills and slides use much less disc space than the motion video created by the transitions, even if the transition is from one slide to another.

The amount of disc space required by each transition varies depending on their length and type. In general, for SD projects, which use a bit rate of 6 Mbps for transitions, you should allow 750 KB of disc space for every second of transition time in the project. For HD projects, which use a bit rate of 20 Mbps for transitions, you should allow 2.5 MB of disc space per second.

Using the Video Bit Rate

The video bit rates you calculate can be used as the bit rate entry of your encoder, regardless of the encoding method you intend to use (one pass, one-pass variable bit rate [VBR], or two-pass VBR).

When using one of the VBR encoding methods in the integrated MPEG encoder, the “Bit rate” setting affects the amount of disc space that the MPEG video file requires, while the “Max bit rate” setting sets the highest video bit rate that is allowed in the file (but does not affect the file size). See MPEG Encoding Methods for more information.