// most recent one. Note that we only need the actual history if we have
// interlaced output (for deinterlacing), so if we detect progressive input,
// we immediately clear out all history and all entries will point to the same
// most recent one. Note that we only need the actual history if we have
// interlaced output (for deinterlacing), so if we detect progressive input,
// we immediately clear out all history and all entries will point to the same