From YouTube Help

Note: This feature isn’t available in YouTube Studio beta yet. If you’re in YouTube Studio beta (studio.youtube.com), select Creator Studio Classic in the left menu to follow these steps. Captions are a great way to make content accessible for viewers. YouTube can use speech recognition technology to automatically create captions for your videos. These automatic captions are generated by machine learning algorithms, so the quality of the captions may vary.

Automatic captions are available in English, Dutch, French, German, Italian, Japanese, Korean, Portuguese, Russian, and Spanish.

If automatic captions are available, they'll automatically be published on the video. Automatic captions may not be ready at the time that you upload a video. Processing time depends on the complexity of the video's audio.

YouTube is constantly improving its speech recognition technology. However, automatic captions might misrepresent the spoken content due to mispronunciations, accents, dialects, or background noise. You should always review automatic captions and edit any parts that haven't been properly transcribed.

Here's how you can review automatic captions and make changes, if needed:

1. Go to your Video Manager by clicking your account in the top right > Creator Studio > Video Manager > Videos.
2. Next to the video you want to add captions or subtitles to, click the drop-down menu next to the Edit button.
3. Select Subtitles and CC.
4. If automatic captions are available, you'll see Language (Automatic) in the “Published” section to the right of the video.
5. Review automatic captions and use the instructions to edit or remove any parts that haven't been properly transcribed.
6. You can also enable the video for community contributions and let your viewers caption and translate your content instead.

If your video doesn't generate automatic captions, it could be due to one or more of the following reasons:

The captions aren't available yet due to processing complex audio in the video. The language in the video is not yet supported by automatic captions. The video is too long. The video has poor sound quality or contains speech that YouTube doesn't recognize. There is a long period of silence at the beginning of the video. There are multiple speakers whose speech overlaps.

1. Click on the User menu in the top right corner.
2. Select Creator Studio
3. Click on Video Manager, from the Left Panel
4. From the Edit button's drop down menu to the right of the video you want to check, choose: Info & Settings
5. Click on Advanced Settings
6. Verify that English is chosen as the Video Language
7. Scroll down to the SAVE CHANGES button, and press the button.