Does chunk size matter in distributed video transcoding?

In recent years, the demand for high quality video streaming services has been growing significantly. Distributed video transcoding in cloud, i.e., re-encoding the source video to best match the capabilities of the network connection and the playback device in cloud and sending each user a tailored version of the video, is a recent solution for fast and high quality video streaming services. In such a transcoding scheme, video is segmented into chunks of equal size and the chunks are distributed among multiple virtual machines for parallel transcoding. The transcoded chunks are then merged together to create the new transcoded video appropriate for playback on specific end-user devices. In this paper, we conduct a performance analysis of the impact of chunk size on coding efficiency and transcoding time. We observe that transcoding with larger chunks leads to better coding efficiency (i.e., lower bitrate) by trading off the transcoding time. The improvement in coding efficiency and the level of trade-off in transcoding time highly depend on the visual similarity among frames of a video sequence. From the analysis, we suggest that for better coding efficiency and faster transcoding, the chunk size should be dynamically adjusted according to the visual similarity.