Why Video files occupy more space than Audio files do?

[smith]

I have many video files in the form of AVI/RMVB/DVDRIP on the hard disk. I
found that these files really occupy much more space of disks than Audio
files like MP3/WMA/RM. Three video documentaries, each of which lasts for 1
hour, may make one DVD-R fully written, but 400 MP3 files that last for 30
minutes each won't take all the space of it. What is the reason?

 

[Bob I]

Simply because it takes a heck of of lot more data to encode a video
stream than audio for any given time frame.

 

[no_one]

video has more bandwidth (bit per second).

 

[Loren Pechtel]

I have many video files in the form of AVI/RMVB/DVDRIP on the hard disk. I
found that these files really occupy much more space of disks than Audio
files like MP3/WMA/RM. Three video documentaries, each of which lasts for 1
hour, may make one DVD-R fully written, but 400 MP3 files that last for 30
minutes each won't take all the space of it. What is the reason?

Because it takes more information to store a picture than a sound.

Think of the difference between a VHS tape and a casette tape.