Knowledge Base

But Webcam Video Looks OK

Problem: Facial Expressions are calculated from face video streams produced by a webcam. So, when the face video is present in liveview, it appears unlogical when no Facial Expression data is produced in the Timeline graph.

Explanation: This is a known issue related to the use of two video processing pipelines: 1) a direct, realtime, processing of video into sequences of images that are sent to the Facial Expressions processor and file storage, and 2) a channel that shows the same live video directly on screen. When only the first process fails, facial expressions cannot be calculated while live video can still be seen.

Solution:

1. Remove and reload Media Plugin in Nlinx-agent on the affected participant stations.
2. If that does not resolve the issue, then restart the NoldusHub server.

Timeline

In Liveview mode, selected signals are plotted for the past 45 seconds. Under perfect conditions, signals fill the graph all the way until the now-line, i.e. the vertical red line that intersects the time axis all the way at the right-hand side of the Timeline graph.

Problem: This is not always the case. The most recent data shown in the graph may go further back in time than a few seconds. There are several explanations for this behavior, each with their own solution:

1. Delayed Data Transfer: Delays in data transfer may be caused by slow or interrupted network traffic. This leads to variable short delays, i.e. jumpy signal lines that go back a split second up to a few seconds, and then jump back to the red line.

   Solution: Improve network connection if any, or just accept the short delays.

2. Clock Sync Issues: The clock of the Test Leader system is not in sync with the NoldusHub server. The NoldusHub server acts as an NTP server for participant stations, but not for the Test Leader system. If either the NoldusHub server or the Test Leader system is not synced to a reliable external NTP server, the Test Leader system will show data that is out of sync in Liveview mode. Signals on the left-hand side of the graph will be missing if the Test Leader system clock time is earlier than NoldusHub server time, or signals will be missing at the right-hand side of the graph if the Test Leader system clock time is later than NoldusHub server time.

   Solution: First, make sure that the Test Leader system is synced with a reliable NTP server. If this does not solve the problem, make sure that the NoldusHub server is also synced with a reliable external NTP server. Please note that data quality is not affected by differences between Test Leader and server clock times as long as participant stations are in sync with the NoldusHub server.

3. Derived Signal Processing Delay: The signal is not a raw live signal, but a derived signal for which signal processing takes time. An example of such a signal is the EDA peak rate signal. EDA peak rates are calculated from raw conductance signals in which EDA peaks are detected. To identify peaks, a full peak needs to be present in the raw signal first. This takes approximately 20 seconds. Therefore, derived EDA signals show delays of 20 seconds.

   Solution: None. The delay is an inherent signal property.

4. Signal Out of Range: The signal is out of range. For instance, heart rates of 250 bpm will be plotted out of view.

   Solution: Check whether the signal is a valid, within-normal-range signal.

Plugin Ping-Pong (v1.6)

As from version 1.6, NoldusHub features plugin reconnect logic. Device plugins can be loaded with the Nlinx-agent application that resides on each participant station. If a device plugin disconnects for any reason, N-linx will try to reconnect. If that succeeds but the reason to disconnect still exists, the plugin will disconnect again. Generally, this sequence of events will repeat without end. This is called plugin ping-pong.

One main reason for the initial disconnect is a stability issue of the used message broker, RabbitMQ. This issue is resolved by assigning dedicated CPUs to RabbitMQ and others to the VideoWebService. A script is run for that during startup (Affinity Settings Script).

Reasons for plugin ping-pong to occur:

1. Script-Wise Affinity Settings Fail Shortly After Server Restart.

   Solution: Initiate affinity settings again by stopping and restarting the NoldusHub server (on-site or in a remote desktop session):

   1. Go to the DockerDeployment folder and run StopNoldusHub.bat.
   2. Wait until all services are properly stopped.
   3. Run StartNoldusHub.bat. Wait for all services to start, then check the plugins in Nlinx-agent. They should all automatically reconnect and stay connected.

After NoldusHub Startup

Problem: Data stream recordings and videos may be incomplete when recordings are made shortly after server restart. When the following steps are performed in sequence without pause, recordings may turn out to be incomplete:

• Run StopNoldusHub.bat and then StartNoldusHub.bat on the server, then immediately select a location and start recording.
• Reboot the NoldusHub server computer, then immediately select a location and start recording.

Explanation: Starting up the many containers needed for NoldusHub takes time and a lot of CPU capacity. These initial processes can take up to 5 minutes to complete. Recording sessions also require a lot of CPU capacity. If recordings are started while containers are still starting up, not all data processing during recording (FES images, cognitive load, EDA data processing, HR & IBI calculation) can be completed in time. Hence, data will be lost.

Solution: Wait at least 5 minutes after restarting the NoldusHub server before starting recordings.

For the Device

This is mostly observed for the webcam: in Liveview, the participant can be seen, but the webcam device in the Signals and Devices page shows an error.

1. This error is not caused by failing video, but by the absence of an audio signal in the composite video-audio output of the camera device. Solution: Check in device setup whether webcam audio is active.

Eyetracker Related

Problem: When using version 1.6.2, it is possible to start recording without calibration. This should be possible; however, in this version it may cause failing workload recordings.

Solution: Always calibrate before starting a recording.

Detected

Problem: After selecting participant stations and switching to Liveview, the video streams of screen capture and participant webcam may disconnect. As a result, facial expression data will also not be available. This is especially observed when the user starts the system but waits before initialising stimulus presentation.

Source: Video disconnects automatically when no video mutations happen on the screen or in the webcam image.

Solution: Start up some dynamic video or other dynamic screen content on the participant screen, or have somebody interact with a window (browser or anything else) on the participant system.

Knowledge Base

Explanations, how-to's, and background information.

Source: NoldusHub 1.7 Tips and Tricks, Noldus Information Technology