Digital Media File Sizes

Understanding the components of digital media files may seem boring, but knowing the basics will help you decide the best ways to produce quality media. The bandwidth and storage requirements are quite high for digital audio and video. Video requires about 27 MB/sec in RGB or 16 MB/sec in YUV. Audio-CD files sizes are about 10 MB/minute. Frame/sample size, frame/sample rate, compression and bit-depth reduction will decrease file size, and thus speed delivery and lower RAM and storage requirements. Best results will be achieved with good quality sources, which produce fewer color and noise artifacts. Just be sure to test early, test often and test on target platforms.

Uncompressed 24-bit Still Graphic

640 x 480 pixels = 307,200 pixels per frame
307,200 x 24 bits per pixel /8 (bits per byte) = 921,600 bytes per frame

The amount bit-depth reduction is greater for graphics with few colors like illustrations. Photographic images require many colors so compression usually give better results.

Uncompressed 24-bit Video
("legal" video is 29.97 fps & thus smaller; YUV color space is 16-bit so files are smaller)

640 x 480 pixels = 307,200 pixels per frame
307,200 x 24 bits x byte/8 bits = 921,600 bytes per frame
921,600 x 30 frames per second = 27.648 MB

Reducing the frame size to 320x240 (one quarter size) and frame rate to 10 fps is simple, but leaves the data rate at 2.3 MB/sec. This data rate is too high for many hard drives, much less CD-ROM (2x drive ~ 200 kbyte/sec sustained ) or modems (28.8 modem ~2.88 kbyte/sec). A good deal of compression will knock this down further, but higher bit-depths make compression look better. Cinepak, Indeo and Power Video are the best codec (compressor/decompressor) choices for CD-ROM playback with QuickTime or Video For Windows. These codecs don't currently support streaming or yield good picture quality at the low data rates required for Web delivery. Solutions for this class of video include Real Media, VDOLive, Xing, TrueStream,Vivo, Vosaic and VXtreme.

Audio File Requirements
(in bytes per second)

Number of samples (sampling frequency in Hz)
x Sample size (1=8-bit,2=16-bit; eg, 8-bit/sample divided by 8 bits per byte)
x Channels (1=mono, 2=stereo)

CD quality audio is stereo, 16-bit, 44.1 KHz which is 176 kbyte/sec -- again too high for CD-ROM (2x drive ~ 200 kbyte/sec sustained ) or modems (28.8 modem ~2.88 kbyte/sec). IMA compression works quite well for CD, but is cross-platform only with QuickTime. RealAudio is the most popular of the numerous solutions for Web audio. For music, MIDI is the best solution for both CD-ROM and Web delivery.

back to Cross-Platform Multimedia Issues

Back to Synesthetic Media Connections

Comments or suggestions welcome at RYoung097@aol.com

SFSU Multimedia Studies Program