•Optical flow accurately measured vibrations 450 times smaller than a pixel.•Optimal processing parameters must be chosen to obtain accurate results.•A systematic method of determining the parameter values should be researched. As digital cameras become cheaper and faster, new opportunities for measuring structural vibration are unlocked. Measuring vibration through video sequences can provide full field measurements of a structure’s motion. Digital image correlation is an established method for measuring structural vibration but requires visual surface preparation of the object being measured. Recently, a new method based on optical flow analysis of video sequences has surfaced that can measure structural vibration without any surface preparation whatsoever. This article presents an experiment to test the accuracy of the new method. The accuracy of the technique is evaluated for several sub-pixel vibration displacement amplitudes. The response is measured by an accelerometer, a laser vibrometer and marker tracking and compared to the optical flow method’s results. The results obtained indicate that it is possible to measure vibration amplitudes 450 times smaller than a single image pixel accurately.