This paper investigates the perceptual quality of decoded video bitstreams after packet losses. We focus on low-resolution and low-bit rate video coded by the H.264/AVC encoder, and packet loss patterns likely in 3G wireless networks. We examine the impact of several factors on the perceptual quality, including the error length (the error propagation duration after a loss), the loss severity (measured by the drop in PSNR due to a loss), and loss location (forgiveness effect). We further propose an objective quality measure based on the findings of our study.