Coding Scheme
The basic idea is to always spend more bits on the foreground, i.e. the human, than on the background.
We apply JPEG to each block and control the compression rate with the quantization steps. Namely, we always use a larger quantization step on background than on foreground, therefore, even with limited bandwidth, the human at the foreground is always clear. ( Limited by the time, the JPEG is not fully implemented, we only utilize the run-length coding for DC and AC coefficiences, which already achieves satisfying results as shown later. )
In addition, we make the quantization step adaptive to the network traffic, which is detected from the receiver by counting the package-lost rate. Right now, a simple proportional feed-back control strategy is used.