In my professional work, a few years ago, I worked on a project where the objective was to make reviews of films and trailers, working through APIs that brought everything together.

The problem is that the subtitles were not always synchronized with the audio and it was very difficult (if not impossible) to find a player that could adjust in real time (at least without wierd plugins and hacks).

A few days ago I started working on a project called “moovie.js”, which is basically a standard HTML5 video, that allows you to adjust the offset manually in real time and has full support for .vtt and .srt caption files.