In this paper, we present adaptation strategies for low-delay video streams over Additive-Increase Multiplicative-Decrease (AIMD) transport protocols, where we switch among several versions of the coded video to match the available network bandwidth accurately, and meet client delay constraints. By monitoring the application buffer at the server, we estimate the current and future server buffer drain delay, and derive the transmission rate to minimize client buffer starvation. We also show that the adaptation accuracy can be significantly improved by a simple scaling to transport protocol send-buffer size. The proposed mechanisms were implemented over Stream Control Transmission Protocol (SCTP) and evaluated through simulation and real Internet traces. Performance results show that the adaptation mechanism is responsive to bandwidth fluctuations, while ensuring that the client buffer does not underflow, and that the quality adaptation is smooth so that the impact on the perceptual quality at the client is minimal.
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