4

Stage 4: 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.
Bit rateAudio format
192 kilobits per second (kbps) to 224 kbpsAC-3 stereo
384 to 448 kbpsAC-3 5.1 surround
754.5 kbps or 1509.75 kbpsDTS 5.1 surround
1536 kbpsPCM stereo 16 bits at 48 kHz
4608 kbpsPCM 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.
Disc spaceBit rateDurationSection
2.32 gigabits (Gbit)448 kbps5174 secondsVideo 1, AC-3 5.1
1.16 Gbit224 kbps5174 secondsVideo 1, AC-3 stereo
4.20 Gbit1536 kbps2735 secondsVideo 2, 16-bit 48 kHz
PCM
0.004 Gbit224 kbps17 secondsMenu, 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.
Stage 5: Calculating the Effect of Audio on the Video Bit Rate
Now that you know how much disc space is required for the audio, you can more
accurately determine the video bit rate you can use. Because the DVD-5 and DVD-9 discs
were the only practical ones based on the previous calculations, you will continue
experimenting with them in this example.
638 Appendix C Calculating Disc Space Requirements