
The current version is 1.6.3 and is available for Windows, macOS and Linux (the Linux version requires Mono). YTSubConverter can produce this file format for you.
Karaoke timing (make the syllables of a song lyric appear as they're sung). Positioning (place your subtitles anywhere on the video). Background coloring and transparency (including hiding the background box completely). For that, you need to use a YouTube-specific format called SRV3 (also referred to as YTT for "YouTube Timed Text"). The site accepts a number of file formats such as RealText, WebVTT and TTML, but all of these come with their own limitations - and most importantly, none of them give access to the full array of features offered by the YouTube player.
If you want formatting such as bold, italic and coloring, you need to upload a subtitle file instead. YouTube's built-in subtitle editor doesn't support styling of any kind.
A tool for creating styled YouTube subtitles.