Streaming multimedia quality is impacted by two main factors: capacity constraint and packet loss. To match the capacity constraint while preserving real-time playout, media scaling can be used to discard the encoded multimedia content that has the least impact on perceived video quality. To limit the impact of lost packets, repair techniques, e.g. forward error correction (FEC), can be used to repair frames damaged by packet loss. However, adding data to facilitate repair requires further reduction of the original multimedia data, making the decision of how much repair data to use of critical importance. Assuming a limited network capacity and the availability of an estimate of the current packet loss rate along a flow path, selecting the best distribution of FEC packets for video frames with inherent interframe encoding dependencies can be cast as a constraint optimization problem that attempts to optimize the quality of the video stream.
This thesis presents an Adjusting Repair and Media scaling with Operations Research (ARMOR) system. An analytical model is derived for streaming video with FEC and media scaling. Given parameters to represent network loss as well as video frame types and sizes, if the number of FEC packets per video frame type and media scaling pattern is specified, the model can estimate the video quality at the receiver side. The model is then used in an operations research algorithm to adjust the FEC strength and media scaling level to yield the best quality under the capacity constraint. Four different combinations of FEC type and media scaling method are studied: Media Independent FEC with Temporal Scaling (MITS), Media Independent FEC with Quality Scaling (MIQS), Media Independent FEC with Temporal and Quality Scaling (MITQS), and Media Dependent FEC with Quality Scaling (MDQS).
The analytical experiments show: 1) adjusting FEC always achieves a higher video quality than streaming video without FEC or with a fixed amount of FEC; 2) Quality Scaling usually works better than Temporal Scaling; and 3) Media Dependent FEC (MDFEC) is typically less effective than Media Independent FEC (MIFEC). A user study is presented with results from 74 participants analysis shows that the ARMOR model can accurately estimate users' perceptual quality. Well-designed simulations and a realistic system implementation suggests the ARMOR system can practically improve the quality of streaming video.