Video time study: recording, analysis and briefing operators
In one sentence
A video time study measures element boundaries using the recording's time information; frame interval, visibility and verification of the time base determine measurement limits.
By the end of this lesson
- Calculate the 0.04 s frame interval of a 25 frames/s recording and report resolution correctly.
- Calculate element and cycle times from frame differences in a constant-frame-rate recording.
- Choose to record again when a boundary is hidden or the time base is unreliable.
- Check differences between two observers' boundary selections and element reconciliation.
Why it matters
A video time study lets you return to the same cycle and examine element boundaries. An event missed in live observation can be assessed later if it is clearly visible in the footage. Define start and end using physical events, as in earlier lessons. Video does not make these definitions unnecessary. Replaying a recording does not automatically make a hidden contact visible. Measured time is initially observed time too; performance rating, allowance and sample sufficiency are separate steps. Marking the same recording several times does not create new independent cycles. Video can strengthen the measurement trace; replay count does not increase the amount of process information collected.
Frame rate determines time resolution in a constant-rate recording. At 25 frames/s, time between consecutive frames is 1 s ÷ 25 = 0.04 s. This recording represents event boundaries in 0.04 s increments. More decimal places do not provide finer time resolution. If footage is blurred or an event is behind a hand, uncertainty can exceed one frame interval. The frame interval alone therefore does not guarantee accuracy. Measurement uses the recording's actual time information, not the observer's time in front of the screen during slow playback. Playback speed aids observation; it is not the work's actual duration.
For a constant-frame-rate recording, divide the difference in frame numbers by frames per second. The same rule may not be directly reliable with variable frame rates or edited or sped-up footage. Verify the file's time information, interruptions and relationship to actual work time. If timestamps are used, check that they too are reliable and in increasing order. Missing or duplicated images are a separate problem from visibility. Before marking boundaries, examine both the image and time base in a short test recording. Otherwise, carefully selected boundaries can be linked to the wrong time scale. Clear images and a correct time base are both required.
Obtain workers' informed consent before recording; clearly explain the purpose, which work section will be studied, who will access the recording and how long it will be retained. Consent must not be used to pressure workers to speed up or collect footage for unclear purposes. Record only the area needed for measurement; exclude faces, name badges, screens and unnecessary conversations. Restrict access by role, set the retention period and person responsible for deletion, and delete at the end of that period. If the purpose or sharing scope changes, the recording is not automatically suitable for the new use. Make privacy decisions as part of the safe observation plan, not after filming.
Formula
Time at a constant frame rate (s) = Frame number difference (frames) ÷ Frame rate (frames/s)
Frame interval (s) = 1 ÷ Frame rate
Time from timestamps (s) = End time − Start time
Cycle reconciliation difference (s) = Union of element intervals − Cycle time
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- Step-by-step instructions
- Worked example with real numbers
- Where the method misleads
- Common mistakes
Lab instructions: Video time study
- Measure 10 cycles at every station.
- Enter the elements with the names below and in this order. Each element starts at its start point and ends at its end point.
- Enter the operator's elements and waits on the Operator track and the machine's running on the Machine track; a machine row runs from the moment the machine starts until it stops.
- Enter a wait or a machine run as a row of its own every time you see it. Assign every row to its station.
1.Pick up the body, clamp it in the fixture
Starts: right hand reaches for the bodies · Ends: clamp lever goes down, hand lets go
2.Fit the seat
Starts: left hand reaches for the yellow seat box on the top shelf · Ends: white seat sits in the body
3.Place the ball
Starts: left hand reaches for the ball tray · Ends: ball sits in the seat
4.Fit the cap by hand
Starts: right hand reaches for the cap box on the top shelf · Ends: cap is seated by hand, right hand lets go
5.Tighten the cap with the screwdriver
Starts: right hand reaches for the screwdriver on the bench · Ends: screwdriver is put down on the bench, hand lets go
6.Open the clamp, put the valve on the belt
Starts: right hand reaches for the clamp lever · Ends: valve is put down on the belt