HOW MUCH? : The question is often asked,

"How much digital video can I fit on a CD-ROM?" or
"How big a server do I need to hold my streaming files?" or
"How big a firewire drive do I need to store my digital video and audio files?"

Given the number of parameters and compression options possible when optimizing digital video for distribution, the answer could be,

"How long is a string?"

FORMULA FOR DISC SPACE: There are three key variables that can be manipulated in order to determine the relationship of a compressed video to its storage requirements:

1. Disc space available (measured in KiloBytes)
2. Data rate for every second of the movie (measured in KiloBytes)
3. Duration of the movie (measured in seconds)

Given two of the variables, the third can be calculated using this formula:

Disc Space (KBytes) = Duration (secs) X Data per second (KBytes)

Don't forget to convert your movie's data rate from kilobits/sec to kilobytes/sec. Roughly, divide the kilobits by 8.

CD-ROM EXAMPLE:

• If you decided to compress movies at 300 KiloBytes/sec for storage on a 640MB (640,000KBytes) CD-ROM disc, then we could place 35 minutes of video on the disc.
• If you decided to compress movies at 100KBytes/sec using the Sorenson codec for storage on a 649MB (640,000KBytes) CD-ROM disc, then we could place 106 minutes of video on the disc (320x240, 15fps).
• Don't forget that if you include a user interface program like Authorware or Director on the CD, you space will be more limited.

   

• NON-LINEAR EDITING PROJECT EXAMPLE:

• If you had 2 hours of raw footage shot in DV video (data rate = 3000KBytes/sec), your raw footage would require at least 360-400MB of storage space

Although it seems easy to decide on the data rate of your movies, recall that dozens of factors play into that figure, such as frame size, frame rate, type of codec with its compression ratios, and the quality and compression of the audio track.

EXAMPLE FILE SIZES FOR 30 SECOND CLIPS:

Duration	Data Rate	Frame Size	Frame Rate	File Size	Sample
30 sec	100 KBytes/sec (800 Kbits/sec)	320x240	15fps	2.6MBytes	CD-ROM
30 sec	230 Kbits/sec	320x240	15fps	820KBytes	Stream
30 sec	56 Kbits/sec	192x144	7.5fps	190KBytes	Stream
30 sec	28 Kbits/sec	160x120	7.5fps	110KBytes	Stream
30 sec	up to 113 kbits/sec	192x144	varies	893KBytes Surestream	Stream

EXAMPLE FILE SIZES FOR 60 SECOND CLIPS: