Extract subs from MP4 with SubtitleExtractor
SubtitleExtractor is a simple tool used to extract subtitles including multiple subtitle tracks from MKV, MP4, M4V, etc. into SRT subtitle files.
You can download it from the site:
Step 1. Launch SubtitleExtractor GUI.exe, then drag and drop an MP4 file to the "Drag and Drop Files Here" field.
Step 2. After that, the software will automatically generate a subtitle file in the folder where the original video file locates. You need to wait for the Pause button to turn gray and unclickable, which indicates that the extraction has finished.