Wearing face mask is an effective measure to reduce the risk of COVID-19 infections and control its transmission, thus its usage survey is important for better policy decision to mitigate the epidemic spread. Current existing worldwide surveys are mostly self-reported, whose accuracies are hard to guaranteed, and may exaggerate the percentage of face mask wearing. Therefore, we collected busking videos with a large amount on YouTube from December 2019 to December 2020, mainly from South Korea, and reported an objective investigation of face mask use in the crowds outdoor. It is found that the face mask wearing rate has an obvious positive correlation with effective reproductive number (Rt) in the South Korea, which indicates that the people in South Korea kept sensitive to the COVID-19 epidemic. The face mask wearing rate in South Korea is higher than some other countries, and two rate droppings in June and September also corresponds to the temporary remission in 2020. This study shows significant potentials to utilize public big video data to make an accurate worldwide survey of face mask use with the support of deep learning technology.

翻译：佩戴口罩是降低COVID-19感染风险并控制传播的有效措施，因此其使用调查对于制定更好的缓解疫情扩散的政策决策至关重要。现有全球范围的调查大多基于自我报告，其准确性难以保证，且可能夸大口罩佩戴比例。为此，我们收集了2019年12月至2020年12月期间YouTube上大量韩国街头表演视频，对户外人群中的口罩使用情况进行了客观调查。研究发现，韩国的口罩佩戴率与有效再生数（Rt）呈现明显正相关，表明韩国民众对COVID-19疫情保持敏感。韩国的口罩佩戴率高于其他国家，且在6月和9月出现的两次下降与2020年的疫情暂时缓解期相对应。本研究展示了利用公共大数据视频，在深度学习技术支持下进行全球范围口罩使用准确调查的显著潜力。