// Package advertising holds what is known about the shape of inserted advertising, for the
// packages that have to recognise it.
//
// It exists because one measured figure -- the length of an ad slot -- had been written out four
// times, in skips, transcript (twice) and signature, each copy carrying a comment pointing at the
// others: "the same unit skips.Classify uses", "the same figure the length-gap rule uses", "one
// ad unit from the start". The agreement was real and deliberate, and recorded only in prose, so
// a corpus that revised the figure would have moved one copy and left three.
package advertising

// UnitMs is the length of one advertising slot.
//
// Advertising is sold in units of roughly fifteen seconds -- the owner's own observation, borne
// out by the corpus -- and three separate rules depend on that same fact:
//
//   - a served file exceeding its declared length by less than one unit cannot carry a real
//     insertion; it is the feed being approximate, the way encoders disagree about a file's
//     length by a fraction of a second;
//   - anything briefer than one unit is a mention rather than a break, and skipping it would
//     clip the programme;
//   - one unit from the start of a guessed break is far more audio than a landmark fingerprint
//     needs, and is the part most certainly advertising rather than programme.
//
// Changing this changes all three, which is the point of it being one constant.
const UnitMs int64 = 15_000