Schema/DTD for Youtube json3 transcript format

Question

I used yt-dlp --skip-download --write-auto-sub --sub-format json3 $target_url to download a Youtube video's captions/transcript. The JSON starts with this key-value:

wireMagic: pb3

Is there a schema definition (JSON Schema, DTD, etc) for this wireMagic format?

I Googled it and also searched the yt-dlp and youtube-dl Github projects. But found no details.

The transcript's JSON body contains many cryptic keys, such as wsWinStyles, mhModeHint, juJustifCode, sdScrollDir, wpWinPositions, apPoint, ahHorPos, avVerPos etc, which I'd like to understand.

Is it a Jsonified version of a web or pre-web captioning standard? Or maybe, is it an internal Google/Youtube caption format?

Answer 1

It doesn't seem to be a standard because it's not written anywhere, It's an internal format of subtitles in Google/YouTube.