Adaptive video streaming: pre-encoded MPEG-4 with bandwidth scaling

摘要

The increasing popularity of streaming video is a cause for concern for the stability of the Internet because most streaming video content is currently delivered via UDP, without any end-to-end congestion control. Since the Internet relies on end systems implementing transmit rate regulation, there has recently been significant interest in congestion control mechanisms that are both fair to TCP and effective in delivering real-time streams. In this paper we design and implement a protocol that attempts to maximize the quality of real-time MPEG-4 video streams while simultaneously providing basic end-to-end congestion control. While several adaptive protocols have been proposed in the literature [An End-to-End rate-based congestion control mechanism for real-time streams in the Internet, in: Proceedings of INFOCOMM'99, March 1999; IEEE Trans. Multimedia 3 (2001) 339], the unique feature of our protocol, the Video Transport Protocol (VTP), is its use of receiver side bandwidth estimation. Such estimation is transmitted to the sender and enables it to adapt to network conditions by altering its sending rate and the bitrate of the transmitted video stream. We deploy our protocol in a real network testbed and extensively study its behavior under varying link speeds and background traffic profiles using the FreeBSD Dummynet link emulator [Dummynet and Forward Error Correction, in: Proceedings of Freenix'98. June 1998]. Our results show that VTP delivers consistent quality video in moderately congested networks and fairly shares bandwidth with TCP in all but a few extreme cases. We also describe some of the challenges in implementing an adaptive video streaming protocol.