Suppose I developed a novel video compression algorithm that compresses video in a higher rate than commonly seen method, and I patented it. Now I want to discover whether some other companies might be compressing video with my method without licensing my patent, but I don't really know how.
If I see a video file from a company that has the similar compression rate, I can only suspect that this company infringes. If I contact the company, they will likely deny it and say they are compressing the video with their own method, and it's impossible for me to request them to show me the source code to see what algorithm they are exactly using.
How is patent infringement usually being discovered?