Bitrate will affect the recording file size.
The higher the bitrate is, the better image and audio quality will be, and the bigger the file size will be.
The lower the bitrate is, the image and audio quality and file size will show the opposite results.
The way of calculating the recording file size is shown below:
Bitrate (kb/s, Bitrate/8)
3600 (seconds, 1hour)
24 (hour, 1 day)
30 (days)
4 (camera numbers)
1 camera for one day: 1080P camera, Record 1 day, 1 Channel（normally 1080P Bitrate is 2048kb/s）
2048/8 x 3600 x 24 x 1 x 1 = 22.1GB
With 1000 GB memory it will record 45 days history for one camera or 11 days for 4 cameras.