youtube-dl keep both auto-generated subtitles and prewritten ones

The other answer is wrong and actually misleads and wastes people's time with this "latest version" thing which is an issue on his end and has nothing to do with the question...

The actual answer is that youtube-dl names its subtitle files only with the language in it (ex: file.en.vtt), which means that a potential auto-en would be named the same way as en, hence the resulting rule that real subtitles will always be prioritized over auto subtitles if both are asked for in the command. This is something that needs to be asked of the devs if we want to be able to do it with youtube-dl alone.

Source :

https://github.com/ytdl-org/youtube-dl/issues/1412

Done, but currently --write-sub --write-auto-sub --all-sub would download en, fr, auto-es. Downloading both en and auto-en would require creating a new field in info dicts for automatic captions.

I had same problem with your video. When I used the --write-auto-sub switch (which writes automatically generated subtitle file) I ended up with this:

[youtube] kHYZDveT46c: Looking for automatic captions
WARNING: Couldn't find automatic captions for kHYZDveT46c

Then I update youtube-dl to the latest version and problem solved!

sudo pip install -U youtube-dl

so make sure you are using the latest version.

[Edited]

As discussed here before, manually created subtitles are preferred over automatic captions, because the automatic captions come from translating manual subtitles or from translating audio/speech recognition of the audio sources.

so for example, if the available subtitles are en, fr, automatic-caption-en, automatic-caption-es:

--write-sub --sub-lang en: Download en
--write-sub --write-auto-sub --sub-lang en: Download en
--write-sub --all-sub: Download en, fr
--write-sub --write-auto-sub --all-sub: Download en, fr, automatic-caption-es