The previous detector substring-matched "TFF"/"BFF" against idet's own label text, so it returned true on every source, and `cmd.Start()` was never paired with `Wait()`, leaving a zombie ffmpeg per file. Run idet bounded with `-frames:v 400 -an -sn -f null -` so it completes, use CombinedOutput so the child is reaped, and parse the "Multi frame detection" summary line — interlaced only when TFF+BFF > Progressive.