There exist inline insertion signalling standards (e.g. SCTE-35). These could be used for the insertion of ads. However, none of this signalling typically mak

There exist inline insertion signalling standards (e.g. SCTE-35). These could be used for the insertion of ads. However, none of this signalling typically makes it into the final over-the-air or cable broadcast and so is not useful for ad detection. To your question on segment lengths, ad spots have specific, predefined duration. In the US these are typically 15s, 30s and 60s (sometimes 45s). This property could be exploited to detect ads. Consider, for example, a video segment that's exactly 30s in duration and is repeated many times over multiple TV channels. It is very likely to be an ad.