Downloading and stream conversion: supporting interactive playout of videos in a client station

Abstract

In this paper we address the problem of supporting interactive playout, both forward and backward, of an MPEG encoded video stream at a player device. We propose a method for transforming the standard MPEG stream to a local form at the player device, which then enables the device to support interactive playout even when the buffer space available is constrained. Specifically, we devise a stream conversion scheme that encodes P frames as I frames after the decompression and playout of each P frame. Such a scenario of transforming a P frame to an I frame is termed P-I conversion. Note that since this P-I conversion is performed after a P frame is decompressed and played out, there is no extra cost required for decoding. Also, since there is no motion estimation and compensation required for compressing a single frame into an I frame, this I frame encoding is done very efficiently. We have evaluated several potential interactive playout methods using video experiments. P-I conversion is shown to be cost-effective, easy to implement, and able to provide interactive playout with high visual quality, and is therefore deemed a viable approach to supporting interactive playout for MPEG video in a client station.