There are selectable presets from libx264 video codec. They were provided to match a machine encoder performance(usually rely on CPU). [Figure 10] renders how fast of each preset is related to video files size. No wonder, the ultrafast produced a video in the least time usage while the veryslow used the most time to complete a task. As FFmpeg document stated, the ultrafast had the biggest file size in the mean time that the very slow had the smallest file size. This is a trade-off theory, the best quality has a slowest process