PSNR control for GOP-level constant quality in H.264 video coding

For some multimedia applications, like storage or surveillance, it may be desirable to encode the content at constant quality level; the encoder should be aware of media content and set suitable parameters. In this work, we analyze the case of video. We propose an algorithm to adapt the quantization, to obtain constant PSNR. This algorithm selects each frame´s quantizer level by comparison with the average of PSNR over N preceding frames, and modifying the quantizer accordingly. This system proved to obtain the target average with a variance in the order of 0.3 in most of the cases. Furthermore, the application may require a per-GOP constant PSNR, like in semantic-based video coding. To obtain this effect, we propose a method to track a given PSNR pattern. The proposed algorithm is able to achieve the target PSNR for each single shot, with a convergence time of only few frames after shot boundary