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MOS Score

What is a Mean Opinion Score or MOS?

September 12, 2019

Mean opinion score (MOS) is a measurement of the quality of experience, commonly used in profiling the quality of audio and video content. HeadSpin’s AI engine continuously measures video mean opinion score of mobile application video during a performance session test. The following is a screenshot of Video Quality MOS on HeadSpin’s waterfall UI timeline highlighted with a red outline.

MOS Performance Metric in HeadSpin’s waterfall UI


Performance Session Link:

Video contents are incorporated in different types of mobile applications: live streaming sports and events, live streaming news, explanation video, cutscene in a game, introduction/walkthrough video, live communication video, video as a file, etc. Poor video experience can negatively impact a user’s overall experience. It is crucial for mobile developers and QA teams to understand how well their video performs on real devices in real network conditions.

HeadSpin’s AI Engine MOS Score

The HeadSpin Video Quality MOS time series can be generated for videos captured directly on the HeadSpin Platform or for videos supplied to the server through an API. This algorithm provides an estimate of the Mean Opinion Score (MOS) for each frame in the supplied video, ranging from a minimum MOS value of 1 (corresponding to Very Poor quality) to a maximum MOS value of 5 (indicating Excellent quality). This estimated MOS is computed by analyzing an aggregated region of video data around the frame index as the analysis progresses through the frames in the video.

MOS score range:

  • MOS 1: Very Poor
  • MOS 2: Poor
  • MOS 3: Fair
  • MOS 4: Good
  • MOS 5: Excellent

iPhone X Video Examples
MOS Score: 3.54 [Youtube video]


Comments: Although the content of the Chinese character and QR character are not crystal clear, no visible blockiness can be observed.

MOS Score: 2 [NBA Video with blur and blockiness]

NBA Video with blur and blockiness

Comments: Notice that the player on the video screen capture is blocky. The scoreboard on the video is blurry.

MOS Score: 0.57 [Youtube Video with severe blockiness]


Comments: Notice that the video is very blocky where the face of the person is indistinguishable.

Improve your video and delight your customers

With real networks on real devices, many factors can affect the delivery of video content through mobile applications. The following list includes some of these different factors:

  • The device and OS of the mobile application
  • Bandwidth, latency, jitter packet losses of the network
  • Misconfiguration of the content delivery network (CDN)
  • Mobile application client issue playing the video
  • Corrupted video download

Using HeadSpin’s platform video mean opinion score (MOS score) and network performance capture, developers and QA teams can resolve issues and improve mobile video viewing experience, which ultimately leads to delighted customers.


1. What are the key performance indicators (KPIs) assessed when conducting a video stream test?

Ans: The video stream test evaluates a range of key performance indicators (KPIs), including Video Quality MOS, Blurriness, Blockiness, Contrast, Brightness, Colorfulness, Downsampling Index, Page Content, Frame Rate, Janky Frame Count, Frame Deadline Missed, Frame Render Time p50, Frame Render Time p90, Frame Render Time p95, and Frame Render Time p99.

2. What is web real-time communication (WebRTC)?

Ans: Web real-time communication (WebRTC) is an open-source project that enables real-time voice, text, and video communications between web browsers and devices. 

3. Which metrics are shown in the Waterfall UI of the HeadSpin Platform while testing a video?

Ans: The metrics available in the Waterfall UI are Blockiness, Blurriness, Contrast, Colorfulness, and Brightness, which show how the video quality evolves in the context of the network traffic, device metrics, and the video recorded from the device screen.

4. Why is the content delivery network (CDN) important for video streaming?

Ans: The content delivery network (CDN) is vital for video streaming because it is closer to viewers than the origin server. Serving the stream from the cache can cut down the round-trip time (RTT) to and from the origin server, which makes CDN significant in video streaming. Also, using a CDN can reduce the possibility that bandwidth issues will slow down the live stream for viewers.

What is a Mean Opinion Score or MOS?

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