ADS Technologies USBAV-708 INSTANT VIDEOMPX, User Manual

Page: 33 / 116

The
Guide
33
Bi
tra
te
m
od
e
Wh
a
t is
th
e b
itr
a
te
?
- B
itr
a
te
c
a
lc
ula
tion
Bitrate calculation
60 minute video with 128 Kbps MP3 audio for 700MB CD-R
1. Calculate how many seconds long the video is
60
The number of minutes
x 60 The number of seconds in one minute
= 3,600 seconds duration
2. Calculate how many bits in total there are available
700
The number of megabytes
x 1,048,576 The number of bytes in one megabyte
x 8 The number of bits in one byte
= 5,872,025,600 bits available
3. Calculate how many bits will be consumed by audio
128
The number of kilobits per second for audio
x 1,000 The number of bits in a kilobit
x 3,600 The duration of the video in seconds from step 1
= 460,800,000 bits consumed by audio
4. Calculate the bits remaining for video
5,872,025,600
The number of bits available from step 2
- 460,800,000 The number of bits consumed by audio from step 3
= 5,411,225,600 bits remaining for video
5. Calculate the video bitrate
5,411,225,600
The number of bits remaining for video
/ 1,000 The number of bits in a kilobit
/ 3,600 The duration of the video in seconds from step 1
= 1,503 kbps video bitrate
Note: Considering the AVI container itself requires some bits we might use
a slightly lower bitrate to ensure hitting our target, e.g. 1,501 kbps