Video Quality Monitor

For offline measurement results: In the main menu, the most frequently selected choice displays the list of processed videos. In this list, each video is represented by a unique number, its test campaign (that enables to gather several results), its file name, its full path, the description of its video and audio streams (codec, dimensions, frame rate, duration, etc...), its video quality score and statistics on video quality (min, max, standard deviation).

For each video, several links enable you to display:

• quality curves
• bitrate curves
• curves of blockiness, blur, contrast, flatness, jerkiness and camera noise.

Some other links permit to draw various representations of the perceived quality versus the bitrate or to display the characteristic frames. At last, some links allow to generate perceived video quality analysis reports in various formats (CSV, TXT, HTML).

For online monitoring results: Results (quality curves, bitrate curve, curves of blockiness, blur, contrast, jerkiness, rebuffering durations...) can be drawn between two user-chosen dates and times. The curves can also be drawn in real time, permitting to remotely see VQM's monitoring activity.

In the web interface, audio and video curves are interactive.

Just click on a point of the curve and it will put this point at the center and zoom by a factor of 2. And select a portion of the curve (by dragging your mouse), it will zoom on this selection.

If the frame corresponding to the center of the curve is a characteristic frame, then this frame will be displayed below the curve. And if you have processed several versions of the same video (at different bitrates, for example), you can draw all their curves on a single figure to easily compare them.

You can also get graphical representations of "perceived quality versus bitrate".

This will enable you to determine the bitrate which is required to get a given quality level.

VQM can also measure:

• audio quality (based on bandwidth estimation, audio breaks, saturations and silences)
• loudness, according to international recommendations ITU BS 1770-2 and EBU R128
• audio bitrate

The measurements are made on the decoded audio waveforms and VQM supports the most common audio formats. To use a particular format, you'll just have to install the appropriate audio decoder.

In the main interface, a button enables to manually reset the audio breaks counter.

VQM can measure audio loudness according to international recommendations ITU BS 1770-2 and EBU R128. This loudness measurement computes 5 different values:

• Momentary loudness (denoted "M" in "EBU mode"): instant value of loudness.
• Short term loudness (denoted "S" in "EBU mode"): mean value of loudness over 3 seconds.
• Medium term loudness: mean value of loudness over 15 seconds.
• Gated loudness: mean value of loudness over 15 seconds, ignoring the values which are below two thresholds (first threshold is absolute and equal to -70 LKFS, second threshold is relative and equal to mean value of remaining loudness measurements after first thresholding minus 10 LKFS).
• Integrated loudness (denoted "I" in "EBU mode"): mean value of loudness over all the duration of the audio signal (even if the values proposed by EBU are recommended).

Loudness can be computed in both online and offline modes. This permits to monitor loudness in real time but also to measure loudness from captured signals (like audio video recordings).

Like the other measured data, all measured loudness values are saved and can be retrieved thanks to the web interface.

VQM can also trigger alerts if loudness is greater than a user-defined threshold.

At last, the integration durations for short term, medium term and gated loudness can be modified by the user.

VQM can use a USB GPS antenna (like a bu-353s4 receiver) to record positions during video quality and/or audio quality measurement.

Then each measure is associated to its GPS information (latitude, longitude, altitude, number of used satellites, GPS clock).

VQM can generate maps showing video quality and/or quality with respect to GPS position.

This map indicates the video quality during the playing of a 4K video from YouTube via 4G in a car driving around the city of Nantes, France. One can notice a zone (in red, on top) which is very badly covered by the operator under test.

Put VQM in a backpack or in a car and measure your video quality depending on your localization!

VQM can generate audio/video test signals and use them to measure the synchronization between audio and video (lipsync).

The user can customize many parameters of the generated audio/video test signals:

• the file duration (in video frames)
• the video frames resolution
• the video frame rate
• the audio sampling rate
• the audio channels number

You can even insert your own logo in a test signal.

VQM then saves audio/video tests signals as AVI files containing uncompressed YUV 4:2:2 video frames and uncompressed 16-bit audio samples (PCM).

The audio and video streams contain synchronization marks which are designed to be robust regarding audio and video encoding distortions.

So you can encode this file using the audio/video codecs you want to test. And you can pass the audio/video signal through any system or broadcasting chain you must test.

Thanks to the sample-accurate and frame-accurate synchronization marks contained in the audio/video streams, VQM can compute the skew (misalignement between audio and vidéo) and express it in milliseconds, from a captured file or in real time from an HDMI or SDI capture device.

VQM contains many other features, among which:

• Tasks Manager: when you click on a button, you don't directly perform an action but actually you add a task in a queue. This enables you to continue loading files and measuring them, even if VQM is already working.
• Watch Folder: it enables to detect every file present or appearing (copied or moved) in specified folders (or in their subfolders). When a file is detected, its quality measurement is launched. The Watch Folder enables to process important numbers of files and to monitor a file-based encoding process using VQM (for VOD, for example)
• Automation methods: to facilitate the use of VQM with an important number of files, VQM can load scripts ou be used in command line (with arguments).
• Magnifying glass: to explore the image at pixel level and view the Y, U and V values of each pixel, a magnifying glass is available. This window shows the image content in the neighborhood of the mouse cursor's position.