Other than 640x480 resolutions and 30 FPS, there are many other factors there are required to be considered, such as the audio quality, the audio channels, the video quality.
To elaborate, the audio can be MP3, WAVE, WMA or any other format depending on which camera records it, please see your camera's instruction manual for the default configurations. Even if you choose any of the above audio settings, there is also audio sampling rate to take into consideration, the bit rate (8kbps being worst, 6 mbps being the best).
The video quality can also be variable, for instance, at black & white, the video will take up fewer colors hence less space, at sepia the video will be slightly less space consuming and at full colors, and the video will take maximum place.
At an average of the major cameras being used and the most popular quality settings being used, you can expect the 2 GB SD card can record from 20 minutes to 2 hours of video. at full colors and maximum audio quality, an average camera records at 10 Mega Bytes Per Second and at slightly lowered audio setting it can take around 500 kilo bytes per second.
To elaborate, the audio can be MP3, WAVE, WMA or any other format depending on which camera records it, please see your camera's instruction manual for the default configurations. Even if you choose any of the above audio settings, there is also audio sampling rate to take into consideration, the bit rate (8kbps being worst, 6 mbps being the best).
The video quality can also be variable, for instance, at black & white, the video will take up fewer colors hence less space, at sepia the video will be slightly less space consuming and at full colors, and the video will take maximum place.
At an average of the major cameras being used and the most popular quality settings being used, you can expect the 2 GB SD card can record from 20 minutes to 2 hours of video. at full colors and maximum audio quality, an average camera records at 10 Mega Bytes Per Second and at slightly lowered audio setting it can take around 500 kilo bytes per second.