# 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 to start tracking 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 (see Redo a trial). Note that the Trial Control log files recorded with the previous instance of the trial are deleted.