This paper proposes a novel contactless angular resampling method for motor bearing fault diagnosis under variable speed. This method involves three steps: (1) the instantaneous rotating angle is measured using the Kanade-Lucas-Tomasi object tracking algorithm from a video that is recorded by a high-speed camera; (2) the bearing signal that is acquired using a microphone is resampled in the angular domain based on the accumulated angle curve; and (3) the resampled signal is demodulated to obtain the bearing fault characteristic frequency for order analysis (OA) and fault recognition. This method has been proven effective in diagnosing a set of defective bearings installed on a brushless direct current motor's and a direct current motor's test rigs, respectively. As its main contribution, this paper exploits a novel optical measurement method to estimate rotating speed, thereby avoiding the use of a tachometer and overcoming the limitations of conventional tacholess OA methods.