8.0

Bit rate
MPEG is a format used for storage and transferring. With older formats (e.g. AVI
) you could predict that 20 seconds of movie would result in 20 MB of data. The file size is a direct
measurement of quality.
In the case of MPEG this is different. The amount of data available can be used differently for different
display modes. 20 MB can be 4 seconds of DVD Video or 5 minutes of streaming Internet in thumbnail
format. The quality of an MPEG video is measured by the width of the created data stream, i.e. the bit
rate. This is the amount of data transmitted per time unit indicated in kBit/s or bits per second.
Bits, not bytes, are used, since the data word width has to address the transmission restrictions.
The file size can be calculated from the average bit rate, if its length is known:
F = (BRV + BRA) * t
F...File size
BRV...Bit rate
video
BRA...Bit rate
audio
t...Length in s
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