Direct answer
Check subtitle CPS, WPM, line length and gaps
The subtitle QC checker calculates per-cue reading speed and structural limits instead of guessing whether captions are readable. It reports characters per second, words per minute, line length, line count, cue duration and the gap from the previous cue. Thresholds are editable because delivery specifications differ by broadcaster, platform, language and audience. A warning identifies a rule breach; it does not automatically prove that the subtitle is unusable.