Record video of events for review

By default CV-Scope keeps no pictures of a live camera. It analyses each frame in memory and stores only the events. When you need to see what happened, for example to check a count, to show why an event fired or to keep a visual audit trail, turn on video recording for the experiment. It works with USB, built-in and network cameras. A run on an uploaded video needs no recording, because that video is kept already.

Step 1. Choose what to record

On the experiment page, the Video recording panel sits under Detection and tracking. Record video offers four choices:

A clip per event suits an audit of events: every event keeps the seconds that explain it, and quiet hours take no space. From entry to exit suits a visit you want to watch as a whole: with a clip per event you would get an entry clip and an exit clip with a hole where the person stood in the room, and with this mode you get one file that runs from the entry to the exit. Record the whole run when you also need the time in which nothing was counted, for example to look for people the detector missed.

Step 2. Set up clips around events

1. Set Record video to A clip around each event.
2. Seconds before the event: 5. The clip starts this long before the moment the event describes, so it shows how the person got there.
3. Seconds after the last event: 10. Events close together share one clip. Each new event moves the end out, up to 5 minutes per clip.
4. Events that start a clip: tick the events you want to see, for example Zone entry and Zone exit for the room of guide 04. With none ticked, every recorded event starts a clip.
5. Keep Draw boxes, track numbers, zones, lines and the time into the video ticked. The video then shows what CV-Scope saw: the box and number of each person, the zones and lines, the clock time, and the name of each event as it happens.
6. Video frame rate (frames per second): 10 is enough to follow people walking. Lower values make smaller files. The video never has more frames per second than the run processes.
7. Click Save.

An event can describe an earlier moment. A zone entry is reported only after Ignore visits shorter than, and a zone exit when the tracker gives up on a person. Their clips still start before that moment, as long as the event is reported within 30 seconds.

Step 2b. Or record whole visits

1. Set Record video to From entry to exit (one clip per visit).
2. Seconds before the event and Seconds after the exit work as before: the file starts that long before the entry and ends that long after the exit.
3. Out of sight before a visit counts as over (s): 3. A visit also ends when the object leaves the picture and no exit event ever arrives, for example when the tracker loses someone at the edge of the frame. Raise it for a scene with pillars or furniture people disappear behind.
4. Events that start a visit: leave empty to let any recorded event start one, or tick Zone entry for a room. A Zone exit or a finished Route for the same object ends it.
5. Several people share one file: it runs from the first entry until the last one has left. A visit longer than five minutes continues in the next file, which starts where the previous one ended, so nothing of the stay is lost.

In the test that covers this mode, a visit from 8 s to 40 s produced a single 39-second file (3 s before the entry, 4 s after the exit). The same run with a clip per event produced two clips of about 7 seconds, with the 27 seconds of dwell missing between them.

Step 3. Record

1. Click Start. On Live, the run shows Video on, or Recording while a file is being written, followed by the number of files saved.
2. Click Stop when you are done. A clip that is still being written is finished and saved.

Recording changes nothing else: the counts, events and results are the same as without video.

Step 4. Watch an event

1. On the experiment page, find the run under Runs. Its button reads Video with the number of files. Click it. On the run’s Results, Video review opens the same page.
2. The timeline covers the whole run. Its shaded parts have video, and a red dot in the event list marks each event with video.
3. Click an event. The player opens the file that contains it, 1.5 seconds before the event. Use Play, −1 frame, +1 frame and the speed list to look closely.
4. If you click a moment without video, a note says so.

Under the player, Recorded video lists each file with the time it was recorded, its length, the event that started it and its size:

• Play starts the file from its beginning.
• Download saves it as MP4 or WebM, which common video players open.
• Delete removes one file. Delete all video of this run removes every file of the run and keeps its events and results.

Step 5. Keep disk use and the video under control

• Retention. In Settings, Video retention (days) deletes recorded video that many days after it was recorded. CV-Scope checks once an hour. 0, the default, keeps video until you delete it. Uploaded videos are not affected.
• Deleting a run deletes its video too.
• What is stored. Settings lists recorded video under What this installation stores, with the experiments that record, the number of files and their total size.
• Where the files are. In the data folder, under recordings, with one folder per run. Back them up with the rest of the data folder, as in guide 21.
• No identities. The video shows anonymous track numbers only. Names and plates from the licensed recognition modules are never drawn into it.

How recording works

• The video is made of the frames the run analyses, so every box in it belongs to that very frame. Its frame rate is at most Video frame rate and at most the rate at which the run processes frames.
• The video is written in the background. When the computer cannot keep up, a frame is skipped rather than slowing down the analysis.
• The video follows the run’s clock, so a point in the video is the same moment as the event time. After a pause of more than 3 seconds, for example while a network camera reconnects, a new file starts.
• Clips are saved as H.264 MP4 on Windows. The whole run is saved as WebM, about a third of the size, which takes more processor time to write.

Troubleshooting

• The panel shows a note instead of the choices. The camera plays an uploaded video. Its video is kept already: open Video review from the run’s Results.
• The run has no video. The setting applies to runs started after you click Save. With clips, only the ticked event types start one.
• Live shows Video failed. CV-Scope could not write a file, for example because the disk is full. The analysis goes on without video. Point at the label to see the reason.
• The files are too large. Lower Video frame rate, record clips instead of the whole run, or set Video retention (days).

Next

• Guide 17 judges events one by one. With recorded video it works for live cameras too.
• Guide 21 plans disk space, backups and privacy for a long study.