Calculating the Bit Rates for Each Disc Size
Once you know the play time in seconds and the bit capacity of the different disc sizes,
you can calculate a basic bit rate for each disc size. To do this, divide the disc size by the
play time (7926 seconds in this example).
Bit rate
Bit capacity
DVD name
1.47 megabits per second (Mbps)
11.68 gigabits (Gbit)
DVD-1
2.68 Mbps
21.28 Gbit
DVD-2
2.95 Mbps
23.36 Gbit
DVD-3
5.37 Mbps
42.56 Gbit
DVD-4
4.74 Mbps
37.6 Gbit
DVD-5
8.62 Mbps
68.32 Gbit
DVD-9
9.49 Mbps
75.2 Gbit
DVD-10
13.36 Mbps
105.92 Gbit
DVD-14
17.24 Mbps
136.64 Gbit
DVD-18
These bit rate values should not be considered final at this point because you still have
to take into consideration the audio and DVD-ROM content. However, these values do
provide an indication as to which DVD disc size you will need to use. If your project uses
compressed audio, such as the Dolby Digital AC-3 format, and has little or no DVD-ROM
content, you would need to decide whether encoding at 4.74 Mbps (or slightly less to
ensure the video and audio all fit on the disc) would provide satisfactory results. If so, a
DVD-5 disc should work for this project. If the project includes multiple soundtracks, a
lot of slides or subtitles, and some DVD-ROM content, you may decide it is best to use a
DVD-9 disc size so that everything you want to include will fit on the disc.
Another point to keep in mind is that video assets are not required to use the same bit
rate. For some assets, you may decide that quality is not as important as it is for others,
and choose to use a lower bit rate for them, allowing more disc space for the other video
assets.
Choosing a bit rate that provides satisfactory results depends on the video content and
the encoder you use. In general, bit rates below 4.0 Mbps are marginally acceptable. For
bit rates between 4 and 6 Mbps, you should get good results when using a good variable
bit rate (VBR) encoder, such as the integrated MPEG encoder, or, for more options,
Compressor directly. For rates between 6 and 8 Mbps, you should have no trouble getting
good results even when using a constant bit rate (CBR) encoder. Eight Mbps is usually
considered the highest usable bit rate—the DVD specification allows up to 9.8 Mbps, but
this can cause playback problems on some DVD players and limit your audio options.
For more information on encoding, see
Encoding Video Materials for DVD
.
637
Appendix C
Calculating Disc Space Requirements
Stage 4: