Make sure the video you're trying to download has actual subtitles uploaded from the owner.

You can then use, for example:

youtube-dl --write-srt --sub-lang en 'http://www.youtube.com/watch?v=RHy9_RQbrnQ'

There is also an option to download the automatically generated subtitle files, using --write-auto-sub.

See the youtube-dl documentation.

Make sure the video you're trying to download has actual subtitles uploaded from the owner.

You can then use, for example:

youtube-dl --write-srt --sub-lang en 'http://www.youtube.com/watch?v=RHy9_RQbrnQ'

There is also an option to download the automatically generated subtitle files, using --write-auto-sub.

See the youtube-dl documentation.

Make sure the video you're trying to download has actual subtitles uploaded from the owner.

For example, the one where it fails only offers automatic captioning, which works by analyzing the speech in the video and then transcribing it on the fly:

However, what you want is a video that has "real" captions. Those can be downloaded easily.

For example:

youtube-dl --write-srt --srt-lang en 'http://www.youtube.com/watch?v=RHy9_RQbrnQ'

Make sure the video you're trying to download has actual subtitles uploaded from the owner.

You can then use, for example:

youtube-dl --write-srt --sub-lang en 'http://www.youtube.com/watch?v=RHy9_RQbrnQ'

There is also an option to download the automatically generated subtitle files, using --write-auto-sub.

See the youtube-dl documentation.