subtitle.im

Some YouTube videos already carry subtitles in the picture, so switching on captions stacks a second line over the first and turns the film into a reading test. The subtitle.im extension for Chrome looks for that printed text and can turn off YouTube's own captions when it finds some. Text recognition runs on sampled frames inside the browser, and the site says no frames or subtitle text are uploaded.

When the two lines are in different languages, the extension can close the captions or ask you first, and when it cannot tell for sure, it leaves them on. The help page warns that small or decorative lettering leads to misses and false alarms, as does text in odd places. A hidden caption comes back with Undo in the prompt or the usual CC button.

For videos without printed subtitles, a global mode either opens captions on every video or closes them everywhere, and a third mode leaves the choice to YouTube. Rules can also be set per channel and per video, though a manual CC press still wins for the current viewing. The extension works only on YouTube in desktop Chrome and switches caption tracks that already exist.