ffmpeg -i input.mp4 -map 0:s:0 sub01.srt
if there is not only one subtitle in the video, use
ffmpeg -i input.mp4 -map 0:s:1 sub02.srt
this command can extract the second subtitle.
ffmpeg -i input.mp4 -map 0:s:0 sub01.srt
if there is not only one subtitle in the video, use
ffmpeg -i input.mp4 -map 0:s:1 sub02.srt
this command can extract the second subtitle.