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Captions for TikTok, Reels and Shorts: what each platform accepts

Subtitles for Reels, TikTok and Shorts: what YouTube's help pages document, what we could not verify, and how to cut cues short enough to read on a phone.

By FreeTranscribe 8 min read

Subtitles for Reels, TikTok videos and YouTube Shorts are two separate jobs: what the platform accepts, and what makes text readable on a phone held at arm’s length. Only one of the three documents its captions on a help page we could read on 15 September 2026, so this post says plainly which behaviour is verified and which you have to check in the app yourself. The second job is the same everywhere: short cues, text clear of the interface, and a reading speed someone scrolling can keep up with.

What we could check on 15 September 2026

Platform help centres are not equally readable. YouTube publishes its caption documentation as ordinary web pages. TikTok’s and Instagram’s came back with no article text at all, so the rows for those two are blank on purpose.

Platform Automatic captions Caption file upload What we could read
YouTube Shorts Documented Documented for videos; Shorts not mentioned either way YouTube Help pages
Instagram Reels Not verified Not verified Help page returned no text
TikTok Not verified Not verified Help page returned no text

“Not verified” does not mean “not possible”. It means we would have to guess, and a guessed format or menu path wastes your afternoon. Where the table is blank, open the app and look.

YouTube Shorts is the one with readable documentation

YouTube’s automatic captioning page says automatic captions cover long-form videos and Shorts, in a long list of languages. It also says quality may vary, that mispronunciations, accents, dialects and background noise can make the captions misrepresent what was said, and that you should always review them and edit anything that came out wrong. They may also not be ready the moment you upload.

When you create a Short in YouTube Studio, YouTube says the system automatically adds autocaptions, and that you can customise the colour, font, styling and position, or disable them, by clicking Captions in the bottom left of the Shorts preview. On iPhone and iPad, YouTube’s Shorts page says you tap Captions to start automatic captioning, then edit the font and text colour and make corrections. That page adds a limit worth knowing first: captions are currently available only in certain languages and on certain mobile devices.

Uploading your own file is documented separately, for videos. YouTube’s “Add subtitles and captions” page lists three routes: upload a file, with timing or without; auto-sync a transcript; or type the captions manually against the playing video. Its supported-files page lists SubRip (.srt), SubViewer (.sbv or .sub), WebVTT (.vtt), TTML, DFXP and Scenarist Closed Caption (.scc), among others. Neither page says anything about Shorts in the part that documents uploading, so we cannot tell you whether the upload route is offered for one. If the Subtitles section appears for yours, SRT is on that accepted list.

Subtitles for Reels and TikTok: look in the app, not in a blog post

On 15 September 2026, help.instagram.com and support.tiktok.com both returned pages with no article text, including the articles on reel captions and on TikTok accessibility. So we have nothing verified to report about either: not whether a caption file can be uploaded, not which formats, not what their automatic captions do.

Checking takes a minute. Before you post, work through the editing screen and look for a control named for captions, subtitles or accessibility, and check the app’s settings too, since some caption controls live there rather than in the composer. That editing screen is also where a file upload would appear if it exists. If you find no way to attach one, the text has to become part of the picture, which is the burned-in route below.

Cut the cues shorter than the broadcast 42 characters

Broadcast subtitle style is written for a wide screen. Netflix’s English timed text style guide uses 42 characters per line, a maximum of two lines, and a reading speed of up to 20 characters per second for adult programmes and 17 for children’s. Our own exporter follows those numbers: 42 characters, two lines, one to six seconds per cue, an 80 millisecond gap.

A vertical video is a narrow column, and the text has to be large enough to read at arm’s length, so the same 42 characters either shrink to an unreadable size or wrap into a block that covers the face of whoever is talking. Split the cues further after export. We aim for one line where the sentence allows it, at roughly half the broadcast length, so a cue is a phrase rather than a sentence.

Reading speed still decides whether it works. At 20 characters per second, a 40-character cue needs two seconds on screen. Shorter cues do not let you go faster; they give the eye less to catch per glance, which is what a fast-cut video needs. If the edit runs faster than the words can be read, cut words rather than shrinking text.

No number settles this on its own. Play the draft on an actual phone, at arm’s length, before you post.

Keep the words clear of the interface

Every vertical feed lays its own furniture over your video: a strip along the bottom holding the account name, the post’s own caption text and the sound credit, and a column of buttons up the right-hand side. Text placed under either disappears behind it.

We are not going to give you pixel measurements or a safe-area rectangle, because we could not verify any and they shift with the device, the app version, and whether a viewer has tapped the post’s caption open. The reliable method is to look. Put the draft into the app’s preview screen, where the real interface sits over your real video, and check the first cue, a middle one and the last. Keeping caption text in the middle third of the frame, and out of the right-hand strip, survives most of that variation.

Burned-in text is common here, and a caption file is still better

Burned-in captions are the norm in vertical video for practical reasons: they show wherever the clip travels, they survive a repost, and they need no upload feature to exist.

The trade-off is the one the W3C’s accessibility guidance describes. Most captions are closed captions that a viewer can hide or display; open captions are permanently visible and cannot be turned off. Burned-in text is open captions. Nobody can restyle it, enlarge it or switch it off, and it covers whatever sits behind it for good. The W3C also defines captions as a text version of the speech and the non-speech audio needed to understand the content, a useful reminder that a caption is more than the dialogue.

Use a caption file wherever the platform takes one, and burn text in where it does not. When you burn in, the craft above matters more, because a viewer who cannot read it has no way to fix it.

From audio to captions in four steps

  1. Transcribe the video. Drop the MP4 or MOV onto FreeTranscribe and the audio track is read on your own machine, with nothing uploaded. It needs desktop Chrome or Edge with working WebGPU, it is English only, and it runs OpenAI’s open-source Whisper model at the base size, about 200 MB downloaded once. In our test it ran at about 1.5x real time on a desktop with a graphics card, and took roughly the length of the recording on a thin laptop. This step will not happen on the phone.
  2. Export SRT. The cues come out at broadcast size: 42 characters, two lines, one to six seconds.
  3. Split the cues. Open the file in a free subtitle editor and break the long cues into phrases, then check the reading speed on the ones you shortened. How to make an SRT file covers the format and the editors, and which export you need covers SRT against VTT if a platform asks for the other one.
  4. Upload or burn in. Attach the file where the platform accepts one. Where it does not, burn the text into the picture before you post, and place it from the preview screen rather than a guess.

Read the transcript through before you cut it into cues. Names, technical terms, heavy accents and noisy rooms are where automatic transcription still slips, and a caption is the one place a mistake is impossible to miss.

Frequently asked questions

Can I upload an SRT file to a Reel or a TikTok? We could not verify that either way on 15 September 2026, because neither help centre returned readable article text to us. Check the editing screen in the app before you post, and the app’s settings.

Do automatic captions count as proper captions? They are a starting point. The W3C defines captions as a text version of the speech and the non-speech audio needed to understand the content, and YouTube says automatic caption quality varies and asks you to review and correct them. Read them through before publishing.

One line or two on a vertical video? One, where the sentence allows it. Two lines of 42 characters is a broadcast convention written for a wide screen, and in a narrow column it either shrinks the text or covers the speaker.

Can I do all this on my phone? Not the transcription step. FreeTranscribe runs on desktop Chrome or Edge with WebGPU, so transcribe and cut the cues on a computer, then post from the phone.

Sources, checked 15 September 2026

captionssubtitlesvertical videosrtshorts
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