Crunchyroll Dual Subs by AndyNoob

Crunchyroll Dual Sub (source here)

Web extension created to fix the annoying issue of not being able to use English and English [CC] subtitles at the same time. The extension is still in development but is guaranteed to work on shows such as One Piece where there are both types of subtitles. This extension supports Croptix and Improve Crunchyroll.

Features

Secondary subtitles
When the Crunchyroll watch page is loaded, the extension reads your Crunchyroll profile data for your preferred/selected subtitle language and type. The extension retrieves the episode's subtitle data in the same manner. The alternate subtitle will then be loaded and rendered accordingly by the extension.

Scoped options
A pop-up/sidebar menu is provided by the extension for scoped preference control. With it, you can apply desired options per season, per episode, or globally.

In the menu, there are a few things that you can do:

1. Apply timing offset for the primary subtitles (i.e. the one selected in the Crunchyroll player).
2. Apply timing offset for the secondary subtitles (which is loaded by this extension).
3. Apply subtitle masks to "erase"/hide portions of the primary subtitle.

Subtitle masking
This feature allows you to "erase" portions of non-CC subtitles. This is intended for if, say, the current primary subtitle contains dialogues and is displaying them at the same time as the secondary subtitle's dialogues.

Caveats

Primary subtitles soft-subbing
This extension, by default, soft-subs non-CC primary subtitles (that is, unless Croptix is installed). The reason being both the timing offset and subtitle masking features require the primary subtitles (if it is not CC subtitles) to be rendered locally in order to interact with them.

Dev notes
The dev notes feature of this extension loads dev notes from here (Github Gist). The purpose of this feature is to inform you of any changes/information regarding the future updates of this extension.

Privacy notice
Everything stays on your computer/browser. The extension does not communicate with any external servers other than Crunchyroll's services. Your browser may say that this extension "can read and change your data on sites." That is because this extension adds control elements (such as the subtitle reload button) onto the Crunchyroll webpage, and also reads some of the data loaded by the Crunchyroll player in order to process subtitles.

Credits
While not completely vibe-coded, this project was made with the help of generative AI (Google Gemini, Claude Sonnet, GPT). Prior to version 0.10.0, this project used frazy-parser by ApayRus to parse subtitle files. As of version 0.10.0, ASSJS by weizhenye is used to render ASS subtitles, and srt-vtt-parser by plussub is used to parse VTT subtitle files.