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How to ensure captions and subtitles are legible

Legibility is crucial to captioning and subtitling – after all, both services are effectively useless if the audience can’t read the text on screen. Unfortunately, captions and subtitles are notoriously difficult to read – whether it’s because moving images in the background “distort” text, or because most video compression degrades it, sometimes drastically. It’s not impossible to ensure that your captions and subs are legible – but it does require some effort.

In this post, we’ll list the five things you should do to make sure your captioning and subtitling is crystal clear.

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General guidelines – not hard-and-fast rules

It’s good to keep in mind that these are general guidelines, and not hard-and-fast rules. They were also developed when video quality – even for broadcast applications – was much lower than it is today. With HD and 4K video, video creators can take more aesthetic liberty with on-screen text, including lower thirds, without affecting usability or legibility too much.

Also, with the advent of online video streaming, users can now control the font, size, color, and other aspects of the captioning or subtitling on a video, meaning two things: that this kind of formatting will be out of a developer’s control, but also that users can adjust this content so that it’s ideal for them, meaning that it’s sometimes not so crucial to get these choices right either.

With that said, following are the five tips.

1. Use sans serif fonts

This goes against everything you’ve been told – after all, serif fonts like Times New Roman make text more legible, right? In print, yes. In video, they make text less legible, as you can see in the following side-by-side.


Why? Because serif fonts have a lot more curved lines and shorter angles, mainly in the serifs themselves. This makes text more difficult to see, especially when it is composed of pixels, and in front of a moving, live-action background – which is most video content. For best results, stick to sans serif fonts like Arial or Helvetica.

Keep in mind that this isn’t always possible across languages – for example, if you have an Arabic subtitling project, your font choices will not include what we’d think of as a sans serif font. However, some fonts have less “information” per character, so picking one of them will help legibility. Arabic subtitles services providers can help you pick the right font.

2. Pick a color other than white, and use an outline

Subtitles are traditionally black or white, but this is just because films used to be black and white. There’s no real reason that they can’t be a different color, preferably one that stands out or is uncommon in nature, like yellow. Likewise, adding a border to your text can increase legibility dramatically, since it’ll keep it visible if you have a background that’s the same color.

Keep in mind that borders won’t be useful for all scripts that are more complex, like Asian double-byte languages. For example, Chinese subtitles projects won’t benefit from outlines too much, since they may not “fit” around some of the more complex characters, unless the borders are made thin enough that they may not really make characters stand out.

3. Add a background

Better even than an outline is a semi-transparent background – this will really help your text stand out, and it’s the best solution when legibility and visibility is crucial. For this reason, backgrounds are commonly used for broadcast captions. However, keep in mind that it does obscure a significant amount of picture, and because of that developers try to avoid it. 


However, this is an especially good solution for Asian double-byte languages, Indian languages, Southeast Asian languages, and other languages with complex scripts, since it means that text doesn't have to be outlined.

4. Decide whether or not you’ll need line breaks

Some languages require line breaks at very specific places – think of Japanese subtitles, for example. For these languages, it’s key to insert line breaks if the captions or subs are to be burned to picture. However, if your final output is on a video platform that allows the user to adjust the text settings, adding line breaks will keep text from reflowing properly, creating additional lines that will affect legibility. In these situations, it's better to let text flow, even if the line breaks aren't ideal.

If you’re in doubt about whether or not you’ll need line breaks, it’s better to have them and delete before the final output than to not have them at all.

5. During translation, keep text expansion to no more that 15%

Some languages expand dramatically during translation – this is especially true during Korean and French subtitles projects. However, this text expansion means that the viewer may not be able to read subs in the viewing time allotted for them. For this reason, it’s good to ask translators to stick to a text expansion of no more than 15%. It’ll be tough for them, but it makes a huge difference in inteligibility and usability.

Bonus tip: Do a full check on the final videos

You won’t really know what isn't 100% legible, or on-screen for too short a time, until someone who doesn’t know your content watches it – so make sure that you do a QA before releasing your captioned or subtitled video. Have someone watch your captioned video with the sound turned off to make sure that everything really works. Likewise, ask a non-English speaker to test out your subs. Did they have trouble reading any of them? Did any go by too quickly? Is any content misaligned? Make sure that you allow enough time in your production workflow for this final check – you may be surprised at how much small tweaks will affect usability, comprehension, and engagement with your content.

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