VSYNC--A Novel Video File Synchronization Protocol
Hao Zhang, Chuohao Yeo and Kannan Ramchandran
Video file synchronization between remote users is an important task in applications such as remote video editing. Retransmission of a video file that has been modified only slightly, for the purpose of synchronization with a remote-end copy, is extremely expensive but avoidable. While tools such as rsync have been widely used for exact bit-stream synchronization of files and directories between remote locations, they are not effective with compressed video. Such content-agnostic approaches fail because a minor modification of video could result in a completely different compressed bitstream.
We are investigating a novel approach for performing incremental video file synchronization on two video files at remote ends up to a user-specified distortion constraint through a bi-directional communications link. Our method, which we name VSYNC (for video synchronization), is designed to automatically detect and transmit changes in the modified video file without the knowledge of what was changed. A hierarchical hashing scheme is designed to compare video chunks, converting the high-level content information to a low-level hash stream that is more amenable to the tools of coding theory. Our preliminary results  show impressive gains in transmission rate-savings. In a typical example of two 12s video files with about 10% of the frames being edited, transmission savings of 44% to 87% can be obtained compared to directly sending the updated video files using H.264 and rsync.
We are now extending the work in  by re-designing the hashing scheme in order to transmit modifications on a more spatially fine-grained basis. We are also investigating the use of distributed video coding techniques to exploit correlation between remote copies for an additional rate rebate.
- H. Zhang, C. Yeo, and K. Ramchandran, "VSYNC--A Novel Video File Synchronization Protocol,'' Proc. ACM International Conference on Multimedia (ACM MM), 2008 (to appear).