ffprobe

A video file can be perfectly valid and still carry no audio. A nonstate skip keeps the row visible and holds the pipeline until someone decides.

TL;DR: A supposedly broken MP4 was actually valid, just with zero audio streams. The pipeline now runs ffprobe first, stores an audio_track flag, and emits a visible skip that never marks work done. Frames follow a fixed fps cadence with capped extraction, while audio is downsampled to 16kHz mono WAV for transcription.