A MOS (mean opinion score) rating is a measure of audio or
video quality. In subjective scoring, a user is asked to rate
quality from 1 (bad) to 5 (excellent). This precall test uses
an objective test, calculating the MOS scores based on bitrate,
packet loss ratio, and (for video) resolution. Objective tests
limit the range of scores from 1.0 (poor) to 4.5 (excellent).