This paper points out negative effects on quality of experience of video streaming sessions caused by metadata atom in MP4 movie files. Based on experiments, it is shown that the duration for downloading metadata atom could be relatively large for high-quality full-length movie videos. | VNU Journal of Science: Comp. Science & Com. Eng., Vol. 32, No. 1 (2016) 33–41 Reducing Startup Time in MP4 On-demand Video Streaming Services with Movie Atom Caching Xuan Tung Hoang∗, Tien Thanh Nguyen VNU University of Engineering and Technology, Hanoi, Vietnam Abstract This paper points out negative effects on quality of experience of video streaming sessions caused by metadata atom in MP4 movie files. Based on experiments, it is shown that the duration for downloading metadata atom could be relatively large for high-quality full-length movie videos. This leads to noticeable and disturbing startup delay to users when watching MP4 movies online. According to our model of user behavior, such a long startup delay could result in a large number of ”leaving users” who abandon their video streaming before videos start to play. In order to reduce the startup delay and the portion of users who leave video sessions early, we present a mechanism, called Movie Atom Caching, that reuses previously downloaded metadata atoms or proactively downloads and caches movie metadata atoms at video players before users actually play the video. The mechanism is implemented in our video streaming prototype system. Experiments on the system show that, in typical cases, user experience is significantly improved as startup delay is cut down. Received 05 December 2015, revised 22 December 2015, accepted 31 December 2015 Keywords: Multimedia Streaming, MPEG-4, MP4, User Experience. 1. Introduction decomposed into two parts, multimedia data and metadata. The former, real multimedia data, is contained in mdat atom. The latter, metadata, is stored in moov atom which in turn contains smaller atoms such as trak, stsd, stss, stts, stsz that are important for parsing and decoding data in mdat. As a result, playback of an MP4 stream can be started only after moov atom is successfully received. This leads to a playback startup time and the size of moov atom is crucial factor of the startup .
