If it was possible to know the answer, I suspect we would be surprised at how many people watch videos without the sound on. Strangely enough, it’s one of the areas where the business world had the problem before the consumer sector: one of the original objections to using video in business to business marketing was that “nobody has their speakers on in the office”.
Nowadays that’s not so much of an issue, because our customers are as likely to be dealing with videos we’ve sent them (or which are on our websites) at home, while travelling, or with headphones. However, it’s still possible to increase the viewership of our videos if we offer the option of comprehensible watching without sound.
And of course, we do this with captions.
Now, it’s important not to confuse captions with subtitling. The latter is what we put up for viewers who can hear the audio but not understand it, usually because it’s not in their language. Captions are for those who can’t hear the audio. And there are two types of these: open captions (which are part of the video) and closed captions (which can be switched on and off).
Open captions are part of the video. They may be a transcription of what’s being said, but they may also just be a written narration to accompany visuals, as with a silent captioned slideshow.
Closed captions are the add-on captions, such as those offered by YouTube, mainly transcribing a spoken narrative (although they can go further). They are usually identified by a [CC] symbol, and are held in a separate file which can be edited by the originator and switched on or off by the viewer.
I believe that every video with speech on it should have closed captions. Viewers may just assume they’re available, and click on a video with the sound already down. They’ll quickly switch away if the captions are clearly absent. In addition, captions can help comprehension even for everyday native speakers like you and I. Some people are just drawn to them. Finally, video transcriptions help search engine optimisation, for obvious reasons.
Another reason to add closed captions is that with YouTube at least, captions will probably be worked out and added automatically. And as YouTube itself says: “These automatic captions are generated by machine-learning algorithms, so the quality of the captions may vary. We encourage creators to add professional captions first. 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 transcribed properly.”
Many of your YouTube viewers will always have the closed captions button switched on. What are they seeing?