Automatic Acquisition Method and Empirical Research of Shot Length in Chinese Films based on Machine Vision

Abstract The measurement of shot length is an essential index for the evaluation of cinematographic research. Given the limitations of existing measurement tools, which require human intervention and are constrained by a narrow measurement scale, this paper proposes an automatic acquisition method of film shot length based on machine vision technology. This method is then applied to scale film calculation and analysis. In order to accurately identify the points of editing in a film and thereby obtain the corresponding shot length, the article examines the most commonly used editing techniques in Chinese film. It determines that the most appropriate method for calculating shot length is video motion target detection. After a comprehensive analysis of the three video motion target detection algorithms, it was determined that the inter-frame difference algorithm exhibited the greatest applicability. Subsequently, experimental tests were conducted on positive and negative datasets to produce the optimal threshold for obtaining shot length using the inter-frame difference algorithm. During the course of the experiments, the inter-frame difference method was also optimized algorithmically with a view to realizing the visual reconstruction of film shot length. Ultimately, the supercomputing center was utilized to complete the operation of the shot length data of 1,600 sample films from 1949 to 2019. This resulted in the formulation of a regularity assertion regarding the shot length of Chinese film over the past seven decades since the founding of the People's Republic of China. The research results show that the average shot length and median shot length of Chinese films have experienced three peaks of fluctuation around 1960, 1980, and 2009 (corresponding to the "Seventeen-Year Period", reform and opening-up, and the opening of the film market), yet they demonstrate an overall downward trend. Since 1997, the annual rate of change in film shot length has been increasing, indicating that with the application of new film technologies, film editing has become more diversified and flexible. These findings hold significant implications for reconstructing the history of Chinese film and objectively evaluating its development.