Transmitting video over wireless with good quality is a challenging problem since video may get distorted by bit errors caused by fading and thermal noise. To address this problem, one can use adaptive transmission strategies, e.g., adapt the transmission power or the transmission data rate according to the channel condition. To achieve this adaptive control, we need to have the closed-form relationship between the video layer performance (the control objective) and the parameters in each layer (the control parameters). This paper is to analyze video distortion caused by fading and thermal noise, which we call "transmission distortion". The major contribution of this paper is that for the first time, we provide a method to predict how the transmission distortion process evolves over time, i.e., we obtain the analytical form of instantaneous transmission distortion as a function of system parameters in real-time video transmission over fading channels. We also obtain the analytical form of instantaneous transmission distortion under various conditions, e.g., data partitioning and the condition that one frame consists of multiple packets transmitted over the wireless channel; these results do not exist in the literature. A nice property of our prediction method is that it is not required for a receiver to acknowledge whether a packet is correctly received. Experimental results show that the transmission distortion predicted by our formula agrees well with the true distortion. The prediction formulae derived in this paper are crucial for real-time control in wireless video transmission.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.