YouTube can use speech recognition technology to automatically create captions for your videos.  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.

Keep in mind that if you use auto-generated captions, you will need to revise them for accuracy.

You can also add captions by uploading a caption file to your video. These types of files contain both the text and time codes for when each line of text should be displayed.

Finally, you can transcribe your video and YouTube will automatically line up your text with the speech in the video. You will need to set the timing to sync with your video.

To add YouTube automatically generated captions, use the following steps:

1. Upload your video to YouTube.
2. Click on the link of the video to which you would like to add captions.
3. When the video page appears, click on the Edit Video button.
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4. In the Video side panel, choose Subtitles.  You will need to scroll down through the list to see it.
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5. Click Add.
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6. If you are automatically generating captions, choose Create new subtitles or CC.  If you are uploading a .srt file or other caption file, choose Upload a file.
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7. Edit your captions.  Remember, auto-generated captions are only 70-85% accurate, and the industry standard calls for 99% accuracy or higher.  You will need to edit punctuation, spelling, and speaker changes.
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8. Save your changes.