Motion-Vector-Driven Lightweight ROI Tracking for Real-Time Saliency-Guided Video Encoding

The huge computation burden of state-of-the-art video coding technologies can be mitigated with Region-of-Interest (ROI) techniques that limit the highest coding effort to salient regions. However, the complexity overhead of saliency detection can easily cancel out the speed gain of ROI coding. This work introduces a lightweight ROI tracking technique that can be used in place of compute-intensive ROI detection to guide a video encoder in inter coding. Low computational overhead is achieved by feeding motion vectors (MVs) of a video encoder back to our neural network that is trained for accurate estimation of ROI movement and size changes. The network training is carried out with our new dataset that is also released in this work to foster the development of head tracking techniques in applications like video conferencing. Our experimental results demonstrate substantial speedups with minimal accuracy tradeoffs over traditional salient object detection (SOD) methods. In scenarios, where a single ROI is tracked with a 64-frame detection interval, our solution obtains up to 50-fold speedup with accuracy of 87% and an average ROI center error of 16 pixels. These results confirm that our ROI tracking approach is a potential technique for low-cost and low-power streaming media applications.