Can I watch only a half region of a video with the ratio scaled? As with the illustration, I want to watch a perfect circle instead of an oval and I want the ads removed. Scaling the media player window and placing it out of the screen maybe hides the ads, but it will also hide the subtitle.
On-the-fly transcoding is preferred (maybe VLC can do it?) because transcoding the file may take a long time and may reduce the video quality. But if it cannot, transcoding the file with command line is also welcomed as long as the video quality is kept :).