Knowledge Base

Trial Control When Tracking from Video Files

When Tracking from Pre-Recorded Video Files

EthoVision XT checks conditions using the time in the video file, instead of the real time.

• For conditions based on time: If you select the DDS option, Trial Control is carried out at the speed set by EthoVision in order not to skip video images. This results in the video playing faster or slower than normal (1x), depending on the processor load necessary to detect subjects. For example, if detection requires little processor work, the program tracks the subject faster than normal. A Time condition (for example, Time 60 s) is therefore met earlier than at real time.
• For conditions that use clock time: If you define a condition based on clock time, or schedule a sub-rule with clock time, this is translated into the video start time, that is, the date and time the video file used for tracking was created.

Example 1: You set a Time condition to start tracking After clock time 11:30. The video file was created on March 6, 2008 at 11:00. Once you start the trial, the condition is met half an hour later in the video. If you had set tracking to start After clock time 10:30, tracking would start immediately after starting the trial.

Example 2: You set a sub-rule to start at 10:00 (1st day). The video file was created on March 6, 2008 at 11:00. Once you start the trial, the sub-rule never starts, because the planned start occurs before the initial time of the video. To make a sub-rule start when tracking from that video, set the start time between 11:00 and the video end time.

When Recording Video, Then Tracking

You can choose to record video first with EthoVision XT and then acquire the tracks from the resulting video file. In that case:

• When recording video, Trial Control is turned off.
• When you track from that video, Trial Control is activated, but you cannot control hardware devices.

See Record Video, Then Acquire a Trial.

When Re-Doing a Trial

For video files recorded with EthoVision XT, you can re-do the corresponding trial. Note that the Trial Control log files recorded with the previous instance of the trial are deleted.

Trial Control in Multiple Arenas

Each Arena Gets Its Own Copy of Trial Control Settings

If your experimental setup includes two or more arenas, Trial Control is applied to each arena separately. This means that if a condition is met in one arena, EthoVision XT takes the corresponding action in that arena, not the others. EthoVision XT evaluates the instructions for each arena within the same sample time. The order in which arenas are evaluated is not stored in your data.

Using Zones in Multiple Arenas

A condition or action is not specific to one arena. If the condition is based on a zone, that zone must be present in all arenas and have the same name. If the zone is not present in an arena, Trial Control cannot progress for that arena. Therefore, tracking does not stop unless you set a maximum trial duration or tracking reaches the end of the video. See Control the End of Tracking.

Maximum Trial Duration with Multiple Arenas

Note the following difference:

• If the Trial Control Settings include a maximum trial duration, tracking stops in all arenas simultaneously.
• If the Trial Control Settings do not include a maximum trial duration, and a condition is set before the Stop Track box, tracking does not necessarily stop in all arenas simultaneously. For example, if Start Tracking is set when the subject is found for the first time (as in the default Start-Stop trial rule) and a Time condition of 5 minutes is placed before the Stop Track box, and subjects in two arenas are found for the first time at different times, tracking starts and stops at different times in each arena, with the five-minute duration applied to each subject independently.

View Trial Control Instructions During Acquisition

Overview

During acquisition you can view the status of the trial control instructions. This allows you to check that the Trial Control Rule works as expected — for example, that an action is taken when the subject enters a zone. You can also view Trial Control States, which are time intervals defined by two Trial Control Events.

To View Trial Control States or Events During Acquisition

In the Acquisition screen, click Show/Hide and select Show Dependent Variables. Then select Trial Control Event or Trial Control State.

See Also

• An example in Conditioning Test: View a Trial Control State Variable

Source: EthoVision XT 19 Help - Trial Control Settings, Noldus Information Technology