It is essential for all multimedia makers to understand the constraints that storage devices, playback devices/hardware (cpus, screens and battery life etc) and network speeds impose on media (primarily audio and video) authoring and delivery. Therefore a full understanding of the following concepts is essential.
Data capacity is used to express the capacity of a storage device such as a memory stick, hard drive or optical disc. Storage capacities are discussed here.
The info dialogue box showing the compression codecs, settings,
data rate/size etc for a Hollywood film QuickTime video clip trailer.
"Data size" is the total size of a given file. In the case of audio and video this will be the file's data rate multiplied by the file's duration in seconds.
You will be concerned with data size for the following reasons ...
Data size is expressed in Bytes, KiloBytes, MegaBytes, GigaBytes etc. A website image may typically be several tens of kilobytes (30Kb), audio will be measured in Mb's and video in tens or hundreds of Mb's or even Gb's.
"Data rate" is used to measure ...
Note that data rate is usually expressed in bits, thus 256Kbps = 256 Kilo bits per second (ie 8 times slower than KiloBytes per second).
Clearly audio/video data will arrive in RAM ready to be played faster from an internal hard disc drive than a 56Kbps internet connection. When creating media for web sites it is first essential to profile your end-users and determine their average connection speed. The data rate of the media file will need to be close to or below the network speed if the file is too play quickly and without interruption.
For a more in-depth discussion of Bandwidth click here.