I encoded two videos (ParkJoy and Sintel) in FFMPEG by H.264 with same parameters (GOP size, QP, frame rate, resolution etc.) and obtained rate-distortion plots (mean PSNR of Y channel vs bitrate). I am trying to understand the possible causes for the difference between those two plots; although they have the same resolution, GOP size etc.. The plots that I obtained are given in the following links, and any help would be appreciated.
The difference in the content of the two samples could explain the different performance of the codec. A given configuration of a codec might perform well for a static shot but not perform well for fast motion. At higher bit rates, the effects of codec settings are usually less noticeable.