There are three ways to add captions to YouTube videos. For all three, you must be the owner of the video.
The end product generated by the second and third options is a caption file. Most caption files are plain text files with time codes indicating the start and stop times. Popular caption file formats include SRT, WebVTT, and TTML, all of which are supported by YouTube.
To add captions to videos on YouTube, you must be the owner of the YouTube account where the video is hosted. The specific steps for uploading your caption file change frequently as the YouTube interface is upgraded. However, the general sequence is fairly consistent.
Currently Video Manager is located within the Upload menu, accessed by clicking Upload.
Note: Depending on your YouTube configuration your videos might not be displayed under Video Manager and instead listed under Creator Studio.
Video Manager features a list of all your current videos. Currently each video includes an Editbutton. Click on the Edit button to reveal the Captions option.
The Captions area within Video Manager includes a variety of features for managing your video’s captions and subtitles. One of the options is Upload a File. Select that option, then follow the prompts to upload your caption or subtitle file and identify the language. After you upload your file the new captions or subtitles will be live on YouTube within seconds.
YouTube also includes its own caption editor as well as a variety of other features related to captions and subtitles. For additional information see YouTube’s Help page on Captions.