The MOS reflects the overall experience of the user. It includes effects of initial loading, stalling, and quality variations throughout the video. This is the primary value of concern when assessing the streaming quality.
The value range can be interpreted as follows:
1: Poor
2: Bad
3: Fair
4: Good
5: Excellent
In practice, a perfect score of 5 cannot be reached, since even humans cannot always agree that a video sequence is Excellent. This means that the highest possible score will be around 4.7. Any value above 4 is therefore considered very good.
A value between 3 and 4 indicates issues with the streaming performance. A value below 3 indicates severe problems with the streaming performance. Of course, this is still dependent on the actual setup and there is never an “absolute” MOS.
The MOS output of the ITU-T model corresponds very closely to the user ratings, with a correlation of about 0.85 to 0.9. This is highly accurate, especially considering the multitude of factors that may influence a final rating.