Adaptive video transcoding and streaming over wireless channels

In this work, we investigate the problem of bit rate adaptation transcoding for transmitting pre-encoded VBR video over burst-error wireless channels, i.e., channels such that errors tend to occur in clusters during fading periods. In particular, we consider a scenario consisting of packet-based transmission with Automatic Repeat ReQuest (ARQ) error control and a feedback channel. With the acknowledgements received through the feedback channel and a statistical channel model, we have an estimate of the current channel state, and effective channel bandwidth. In this paper, we analyze the constraints of buffer and end-to-end delay, and derive the conditions that the transcoder buffers have to meet for preventing the end decoder buffer from underflowing and overflowing. Furthermore, we also investigate the source characteristics and scene changes of the pre-encoded video stream. Based on the channel constraints and source video characteristics, we propose an adaptive bit rate adaptation algorithm for transcoding and transmitting pre-encoded VBR video stream over wireless channel. Our experimental results demonstrate that, by reusing the source characteristics and scene change information, transcoding high quality video can produce better video picture quality than that produced by directly encoding the uncompressed video at the same low bit rate. Moreover, by controlling the frame bit budget according to the channel conditions and buffer occupancy, the initial startup delay of streaming pre-encoded video can be significantly reduced.