Subtitles for app promo videos: size, timing and safe areas

Subtitles for app promo videos should be burned into the video itself, because many people watch short-form video with the sound off, and platform captions look different everywhere or can be switched off. Make them large and bold, show two to three words at a time, place them a little below the middle of the frame clear of the platform's buttons and caption, give them strong contrast, and time each chunk to the moment the voice says it.

What are burned-in subtitles?

Burned-in subtitles (also called open captions) are part of the video image itself. They're drawn onto every frame before you export, so they show up exactly the same wherever the video plays, and nobody can turn them off.

The alternative is captions that sit on a separate layer: auto captions that TikTok, Instagram or YouTube generate from your audio, or a caption file you upload where the platform supports it. Viewers can usually switch those on or off, and the platform decides how they look.

For a promo video you'll post in several places, burned-in subtitles are the safer choice. If you use them, leave the platform's auto captions off so viewers don't see two sets of words on top of each other.

Why do subtitles matter so much for app promo videos?

• Plenty of people watch with the sound off. On a train, in bed, at work, in a waiting room. Without words on screen, your voice-over doesn't exist for them.
• They reinforce the hook. Hearing and reading the first line at the same time makes it harder to miss.
• They're accessible. Deaf and hard-of-hearing viewers can follow the whole video.
• They help non-native speakers. Reading along is easier than catching every word by ear.
• They show your app name spelled right. Viewers see exactly what to search for in the App Store.

How big should subtitles be on a vertical video?

Big enough to read on a phone held at arm's length, without squinting or pausing. A good starting point is a bold font sized at roughly 6 to 8 percent of the frame width, which works out to about 45 to 55 pixels on a 720×1280 frame. Then check it on a real phone, because the right size depends on the font.

A few more rules of thumb:

• One line, two at most. With two to three words per chunk, one line is usually enough.
• Leave side margins. Keep each line within about the middle 80 percent of the frame's width.
• Use a bold sans-serif. Simple letter shapes survive compression and small screens. Avoid thin, condensed and script fonts.
• Pick one case and stick to it. All caps works for very short chunks; sentence case is easier to read when chunks run longer.

Why show two to three words at a time?

Short chunks read at a glance. The viewer's eye catches the words and goes straight back to the scene, instead of reading a full sentence while the picture moves on without them. Short chunks also keep pace with the voice, so reading and hearing stay in sync.

Split chunks on natural phrase breaks, the places where you'd pause if you read the line aloud:

• Good: "You take / the phone away / and bedtime / becomes a battle"
• Awkward: "You take the / phone away and / bedtime becomes / a battle"

Keep these together in one chunk:

• Names, including your app name.
• Numbers and their units, like "ten minutes".
• Short contrasts, like "not more", if splitting them changes the meaning.

Drop commas and periods at the end of chunks; they add clutter without helping. Keep question marks and apostrophes, which change meaning.

Many short-form videos also highlight the word being spoken, often in an accent color. It's optional, but it keeps the eye moving with the voice.

Where should subtitles go on TikTok, Reels and Shorts?

On full-screen vertical video, the platform draws its own interface over your picture: buttons down the right side, your username, caption and audio details along the bottom, and tabs or controls across the top. Words placed there get covered.

As a rule of thumb, center the subtitles horizontally and place them a little below the middle of the frame. Each platform's layout is slightly different and changes over time, so before you post widely, upload a test video privately or as a draft and look at it on your own phone. If you post the same file to several platforms, place subtitles where they're clear on all of them; the guide to cross-posting between TikTok, Reels and Shorts covers other differences to plan for.

Watch the scene, too. If a shot shows a key part of your app's interface in the middle of the frame, move the subtitles slightly so they don't cover it.

How to make subtitles readable on any background

Your scenes change every few seconds, from dark bedrooms to bright app screens. The subtitles need to stay readable on all of them.

• Light text with a dark outline or soft shadow is the most common approach, and it works on most backgrounds.
• A semi-transparent dark box behind the text is safer on busy or bright scenes.
• Aim for strong contrast. A widely used accessibility guideline for text is a contrast ratio of at least 4.5 to 1 against its background.
• Use an accent color only for highlights. Pull it from your app icon, and check it still reads against both light and dark scenes.
• Don't rely on color alone. Red and green highlights are hard to tell apart for many viewers with color vision deficiency; pair a color change with a weight or size change.
• Keep the style the same in every video, so your posts look like a series.

How to time subtitles to the voice-over

Each chunk should appear as its first word is spoken and leave as the next chunk begins. Subtitles that arrive early give away the line before the voice gets there. Subtitles that lag make viewers feel the video is out of sync.

At a conversational pace of about two and a half words per second, a two-word chunk is on screen for less than a second. That's fine for short, familiar words. It's also why long chunks don't work: there isn't time to read them.

During pauses, either hold the last chunk until the next line starts or clear the screen. Don't let words flicker on and off. And always build subtitles from the final voice-over, not an earlier draft of the script. If you change a line, regenerate both. Writing the script for the ear helps too; the guide to AI voice-over for app videos covers spelling numbers the way they're said, so subtitles and voice match.

How to add burned-in subtitles, step by step

1. Lock the script and the voice-over. Subtitles come last.
2. Split the script into two- to three-word chunks on natural phrase breaks.
3. Time each chunk to the voice, appearing on its first word.
4. Style them: bold sans-serif, large, high contrast, one line.
5. Place them a little below the middle of the frame, clear of the right edge and the bottom.
6. Add word highlighting if you use it, in one accent color.
7. Watch the whole video on a phone with the sound off. Can you follow the story from the words alone?
8. Watch it again with the sound on to check the timing.
9. Export, and leave the platform's auto captions off when you post.

How to handle subtitles in other languages

• Burn in the language of the voice-over. Make one video per language rather than stacking two languages on screen.
• Write each language natively, then chunk it. Translated lines tend to run long and break awkwardly. The localization guide explains why native copy works better.
• Expect longer words. In languages like German, a single compound word can fill a chunk on its own. That's fine; keep the chunk to one line.
• Chunk by phrase in Japanese, Korean and Chinese. Japanese and Chinese don't separate words with spaces, so split at short, natural phrases instead of counting words.
• Check right-to-left scripts. For Arabic, make sure your tool and font handle right-to-left text and put punctuation on the correct side.
• Check that your font covers the script. Hindi, Russian, Ukrainian and others need fonts that include their characters. Empty boxes in place of letters mean the font is missing them.
• Keep the app name exactly as it appears on that market's App Store listing.

Subtitles in ReelMyApp videos

Every short ReelMyApp makes has burned-in subtitles. You paste your App Store or Google Play link and describe your audience, and it makes a 9:16 video of about 30 seconds (720×1280) in five scenes, with an AI voice-over, instrumental music, the subtitles, a caption and 5–8 hashtags. Because the subtitles are part of the MP4 you download, they look the same on every platform you post it to. A video costs 50 credits, and new accounts can sign up and get 20 free credits after verifying their email.

Key takeaways

• Burn subtitles into app promo videos so they work with the sound off and look the same everywhere.
• Show two to three words at a time, split on natural phrase breaks, in a large bold sans-serif.
• Place them a little below the middle of the frame, away from the bottom and the right edge.
• Use light text with a dark outline or box, and keep contrast strong on every scene.
• Time each chunk to the moment it's spoken, built from the final voice-over.
• Make one video per language, written natively and chunked for that script.

Frequently asked questions

Should I use burned-in subtitles or the platform's auto captions?

Burned-in subtitles for promo videos, because they look the same everywhere and you control size, timing and placement. If you burn them in, leave the platform's auto captions off so the words don't appear twice.

How many words should be on screen at once?

Two to three. Short chunks read at a glance and keep pace with the voice, so viewers can watch the scene instead of reading a paragraph.

Where should subtitles go on a TikTok or Reels video?

Centered, a little below the middle of the frame. Keep them out of the bottom of the frame and away from the right edge, where the platform's caption and buttons sit.

What font works best for video subtitles?

A bold, simple sans-serif with clear letter shapes. Thin, condensed or script fonts break up on small screens and busy backgrounds.

Do subtitles have to match the voice-over word for word?

For a promo video, yes. Viewers notice when the words on screen differ from what they hear, especially when the spoken word is highlighted.

Does ReelMyApp add subtitles automatically?

Yes. Every short it makes has subtitles burned in over the AI voice-over, so the MP4 you download is ready to post with the sound on or off.