The waveform and playback controls
Below the subtitle list, a timeline shows the video's audio as a waveform with every subtitle block drawn at its position — a fast way to see and fix timing.
Playback
The transport has Play / Pause (Space), Skip back 5s and Skip forward 5s (J or ←, and L or →), a time readout and a Speed control. The app extracts the video’s audio for playback when you open it; the timeline says Loading audio… while it works, and Audio unavailable if it fails, with the reason. A file with no audio, including every subtitle-only file, has no playback.
The waveform and zoom
The waveform is read from the video’s own audio and does not wait for playback audio to be ready; Reading waveform… and Waveform unavailable say where it stands. Zoom with the buttons or Ctrl+wheel; zoomed out, a long film still shows everything at once. Each subtitle is a labelled block at its timestamp: click one to select it and scroll the list to its row, and Shift-click to select several.
Retiming against the audio
Play to the moment a line should start or end and press [ or ] to set the selected line’s start or end to the playhead, or use Split to cut a long block where the speaker pauses. See Editing text and timing.