As a general, you will find it hard to gain extra space by compressing menus and buttons, and audio streams will not sound good below certain bit rate settings. Once they are all encoded to your satisfaction you will be able to calculate their total combined file sizes. What's left will help you determine the highest quality compression setting to use for encoding your video streams.
When do you need to calculate the video data rate?
Video files of 1 hour or less will not need the maximum possible data rate calculated because even at the highest rate allowed by the DVD specification (9.8Mbps) they will fit on a disc, and remember, this rate isn't recommended anyway because of the maximum bit rate limit .
Once you project exceeds a hour of video you will find it beneficial to calculate the maximum possible video data rate.
Why are the calculation carried out in bytes?
If media file size and storage usage were calculated in kilobytes or megabytes you would have to constantly convert between DVD and computer storage conventions. Calculating in bytes side steps this issue. After all, a byte is a byte! 8-bits. No arguments!
How do I calculate the maximum possible video data rate?
I thought you'd ask that! OK, Here's how ...
1. What capacity disc are you using?
If you're authoring for the drive on your home computer it will probably be a DVD-R (DVD-5) drive and will have a capacity of 4,700,000,000 bytes. For other capacities click here.
2. Calculate a reserve for unforeseen extra media and files
It is prudent to leave some extra space in your calculations for 2 reasons ...
-
You may find late in the authoring process that you have left out an important element that must be added.
-
The process of multiplexing can create extra files over which you have no control.
Leave 5% of your discs capacity as a reserve.
| DVD disc format | Reserve required |
|---|---|
| DVD-R | 235,000,000 bytes |
| DVD-9 | 427,000,000 bytes |
| DVD-10 | 470,000,000 bytes |
| DVD-18 | 854,000,000 bytes |
3 Calculate audio file sizes
Once you have decided upon a suitable bit rate for your audio streams, calculate the total time of all your streams/files and apply the following calculation ...
- (total audio minutes x 60 x the bit rate) divided by 8 = Total required storage (in bytes)
4. Calculate subtitle file sizes
Each individual on screen subtitle requires 4,000 bytes.
- number of subtitles x 4,000 = Total required storage (in bytes)
5. Calculate still image menu file sizes
Photoshop layer menus ...
- number of buttons on menus x number of button states (active, inactive, up, down etc) x 100,000 = Total required storage (in bytes)
Highlight menus ...
- number of highlight menus x 100,000 = Total required storage (in bytes)
6. Calculate video data rate for video streams and video motion menus
1. Calculate disc space available for video ...
- disc capacity - reserve - audio files - subtitle files - still menu files = Storage available for video (bytes)
2. Calculate the combined length in minutes of all video streams (including motion menus).
- video tracks minutes + motion menus minutes = Total video minutes
3. Calculate video data rate ...
- (storage available for video divided by total video minutes divided by 60) x 8 = Video data rate