Objective quality is separately measured for each media source (audio, video, screen-sharing, etc.). It takes two annoyances into account: variation and lack of timeliness.
Typically, real-time communications have a strict timeline for playback and rendering for the communication to be interactive. ITU-T recommends the maximum threshold for end-to-end (capture to render) latency to be 150ms. Similarly, 300ms end-to-end latency is imposed on video. Most video applications consider changing frame size at short intervals (less than every few seconds) to affect the quality of experience significantly.
Objective quality takes all the above into account and penalizes streams that have the following features (non-exhaustive list):
- Audio or video out of sync.
- Variation in audio or video sync at short intervals.
- Variation in frame size at short intervals.
- Variation in delay.
- Throughput, jitter, audio output, and more.
Objective quality returns a value between 0 and 4dB, where below 1 is considered poor quality and above 2.0 is considered excellent quality.
As always, participants are still able to rate their experience and provide feedback, which can be compared to the objective quality score provided by callstats.io.