Calculating the Audio Allowances
Depending on your project, the audio may have a relatively minor effect on disc space.
It can also be challenging to determine the audio allowances because each video asset
can have up to eight audio streams, and each stream can be a different type and length.
The following table lists the typical bit rates for the common audio formats.
192 kilobits per second (kbps) to 224 kbps
384 to 448 kbps
AC-3 5.1 surround
754.5 kbps or 1509.75 kbps
DTS 5.1 surround
PCM stereo 16 bits at 48 kHz
PCM stereo 24 bits at 96 kHz
In the earlier example, video asset 1 has two audio streams, each 5174 seconds long. The
first stream is AC-3 5.1 surround, and the second is AC-3 stereo. The video asset 2 has
one audio stream 2735 seconds long, using 16-bit 48 kHz PCM audio. The motion menu
has an AC-3 stereo audio stream 17 seconds long. If your slideshow includes audio, you
also need to include that in the formula.
To calculate the storage required, you determine each video asset’s total audio bit rate
and multiply that by the duration.
2.32 gigabits (Gbit)
Video 1, AC-3 5.1
Video 1, AC-3 stereo
Video 2, 16-bit 48 kHz
Menu, AC-3 stereo
Total: 7.684 Gbit
As you can see, using PCM audio requires substantially more disc space than using a
compressed format like AC-3. See
Preparing Audio Assets
for more information on the
different audio formats.