Streaming Video Over Variable Bit-Rate Wireless Channels IEEE Trans. on Multimedia, April 2004 Thomas Stockhammer, Hrvoje Jenka ˇ c, and Gabriel Kuhn

Outline Problem formulation Design of receiver buffer Channel model Simulation results

Related work (smoothing)

Transport of VBR encoded video streams to wired and wireless clients Wireless VBR

Definitions Sampling curve p(t): The overall amount of data produced by the video encoder up to time t. Receiver curve r(t): The total amount of data received error-free up to time t at the receiver. The time to playout x amount of data.

Initial delay & receiver buffer Initial delay: Ex: 1Kbps video, t = 5 sec, r(5) = 3Kb  p (-1) (r(5)) = 3 sec  delay = 5 – 3 = 2 sec Receiver buffer size: (current received data) – (current playout position)

Design of receiver buffer (1/2) Assume the video is transmitted over a CBR channel with rate R. Delay jitter buffer: (transmission) Current time – expected transmission time Decoder buffer: (decoding) Current time – playing time of received data

Design of receiver buffer (2/2) Obviously, using single receiver buffer is more efficient than using separated buffers.

Random receiver curve (1/2) Assumptions r u (t): upper limit r l (t): lower limit R(t): random receiver curve π: the probability that the receiver curve is in between the limits.

Random receiver curve (2/2) For a given sample curve p(t), a given upper and lower limit r u (t) and r l (t) such that and, if the initial delay is selected as and the receiver buffer size as it can guaranteed that the probability of successful playout of the sequence at the receiver is at least π. prevent from buffer underflow prevent from buffer overflow

Channel model (1/3) A transmission system W(C, τ L, p) results in a random receiver curve R(t). C : packet size τ L : transmit time interval X i : a random variable which describes the successful transmission of a packet at time index i. X i = 0 or 1 p : the probability of a successful packet reception (X i = 1). T i : the number of successfully received packets at after i transmission attempts.

Channel model (2/3) T i is binomially distributed, i.e., The random receiver curve is Upper bound Lower bound

Channel model (3/3) Lower limit Upper limit Initial delay Receiver buffer

Outage probability ρ U (p = 0.9) (U: number of packets)

Upper & lower limit, playout curve, shifted playout curve with minimum buffer size lower limit ≥ playout curve upper limit ≤ shifted playout curve C=640 τ L =10 ms p = 0.9 initial delay

Simulation environments Sports News C=640, τ L =10 ms, p=0.9

Simulation results (1/2) upper bound: upper bound v.s. minimum buffer v.s. infinite buffer

Simulation results (2/2)