There was a project that did exactly this, I'll see if I can find the link, most of the work was spent stripping HDCP. The key heuristic in ad detection is that (at least in 2014) there is usually a single black frame between content and advertisements, and ads are rarely transmitted with more that stereo audio, while most content comes as 5.1 or 7.1 channels, even if it is a naive upscale.