Almost all Google's speech recognition system.
Closed captions on YouTube not only help viewers understand the content of the video when they are struggling to pick up the accent but can also help people who are hard-of-hearing. However, since captions and translations are automatically generated by YouTube using machine learning algorithms, the quality of the captions could vary due to mispronunciations, accents, dialects or background noise.
By default, YouTube does not display closed captions for most videos. To enable closed captions, go to the target video and click on the 'CC' icon at the bottom. This will enable closed captions for that video. To disable it, simply click on the same icon once again. As explained by Google, the process is pretty much identical on the YouTube app, although the 'CC' icon will be displayed at the top of the video window in this case. Again, just like on the website, closed captions will be off by default, but s can tap on the 'CC' icon once to enable it or tap on it for a second time to disable it. Viewers can also enable closed captions in the middle of video playback. To do that, just hover over the video with the mouse on the desktop or tap on the video on mobile to see the available options.
Enable Closed Captions On All Videos
The method described above will only enable closed captions on a per-video basis, but s can also enable the feature for all videos at once. To do that on the website, sign in to YouTube on a web browser and click on the profile icon at the top-right corner. Select 'Settings' from the drop-down menu and from the left sidebar on the settings page, select 'Playback and performance.' Now on the right pane, in the 'Subtitles and Closed Captions' section, check the box next to 'Always Show Captions.' s can also enable the 'Include Auto-Generated Captions' option to see captions for more videos. On the app, tap on the profile icon at the top-right corner, select 'Settings,' and then tap on 'Captions.' Finally, turn on the 'Show captions' toggle on the next page.
Closed captions are always in the same language as that of the video, which means for foreign languages, s will also need to enable subtitles to understand the content of the video. To view subtitles on the desktop, first, enable closed captions in the manner described above and then go to the video settings by clicking on the gear icon at the bottom of the video window. Now click on the 'Subtitles/CC' option on the tiny pop-up window and then select 'Auto translate.' Now from the list, select the subtitle language, and YouTube will display subtitles in that language once the video starts playing.
Source: Google