Stream Conversion to Support Interactive Playout of Videos in a Client Station

In this paper we address the problem of supporting interactive playout 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 eecient interactive playout, speciically for backward playout, even when the buuer space available is constrained. Explicitly, 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 using the technique of P-I conversion, backward playout will not require any additional memory buuer than normal forward playout, thus avoiding the large buuer requirement that would be needed for backward playout in the original MPEG stream because of interframe dependencies. It will be seen 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 eeciently. We have evaluated several potential interactive playout methods using video experiments. P-I conversion is shown to be cost-eeective, easy to implement and able to provide high visual quality interactive playout, and is therefore deemed a viable approach to supporting interactive playout for MPEG video in a client station.