Auto-Subtitle a Video with AI, in French

You shot a decent video, it's clear, and it still goes unnoticed because nobody turns the sound on. Subtitling by hand easily takes 30 to 45 minutes of work for 60 seconds of video: writing everything out, splitting it up, syncing each line to the speech. With a transcription AI, that same video comes back subtitled in 2 to 3 minutes, and you're left with two or three words to fix.

This guide walks you through two ways to do it in French: with the built-in features of your phone and social platforms, or with a specialized third-party tool. You'll also see the settings that genuinely matter (text size, position, number of words per line) and the typical mistakes automatic French produces: badly split liaisons, homophones, proper nouns. No technical skills needed: if you can drop a file into a window, you can do this. For the text part, starting with proofreading the transcript, you can get help from the Skilzy chat before going back to the subtitling tool of your choice.

How an AI subtitles a video, concretely

A subtitling AI does three things: it listens to the audio track, it writes out the text, then it syncs each sentence with the exact moment it's spoken.

The first step is called automatic speech transcription. The model analyzes the sound and produces text. The best-known player here is Whisper, OpenAI's open source model, trained on 680,000 hours of multilingual audio, a large share of it French. It's Whisper, or a spin-off of it, running under the hood of most of the tools you'll come across.

The second step is timestamping: the AI attaches a precise moment to each word (00:00:04,120, for example). That's what keeps subtitles from lagging half a second behind, the single most irritating flaw for the eye.

The third step is styling: font, size, color, word-by-word animation. At the end, you get one of two formats.

• A separate subtitle file (.srt or .vtt): a plain text file you upload alongside your video on YouTube, LinkedIn, or a website. Viewers can turn them on or off, and search engines read their content.
• Burned-in subtitles (also called "burn-in"): the text is baked into the image. You can't switch it off, but it shows up everywhere, including on TikTok, Instagram, and Shorts, where playback usually starts muted.

For vertical formats, burning in is almost always the right call. For a long video on YouTube or a website, stick with the .srt file: it feeds the page's SEO too.

Method 1: the built-in features of your phone and social platforms

It's free, it's already installed, and for a story or a Reel you're publishing within the minute, it's often the best effort-to-result ratio.

No reason to hide this option: in plenty of cases, it does the job.

On TikTok. In the editor, open the right-hand menu, then "Captions." The app transcribes automatically in French and lets you correct each line before publishing. You can also generate translations. Styling stays limited to a handful of presets.

On Instagram. Two paths: the "Captions" sticker you drop on top of the video in the Reels editor, or the automatic captions option in your account settings, which turns them on by default. Editing is possible but less comfortable than on TikTok.

On YouTube. After you upload, YouTube generates automatic French subtitles in YouTube Studio, under the Subtitles tab. You can edit them line by line or upload your own .srt file, which is the better move for a video you want to have a long life. These subtitles get indexed, which is a real lever for an AI-powered faceless YouTube channel.

On your phone directly. On iPhone, Apple's Clips app shows live subtitles as you speak and burns them into the video. On Android, several manufacturers offer transcription built into the gallery editor, with availability varying by model and system version.

The limits of this route are always the same: the styling is locked, you don't get a file you can reuse elsewhere, and the transcription happens inside the app you're publishing to. If you're pushing the same video to four platforms, you do the whole thing four times.

Method 2: specialized third-party tools

These make sense when you want a highly polished look, batch processing, or a clean subtitle file to reuse.

Here are the families of tools you'll run into, in no particular order of preference.

Pricing for these services changes often: check the official page before committing, especially on annual plans.

A word on running Whisper on your own machine: it's the cheapest option to use and the most respectful of your files, since nothing leaves for a server. The trade-off is that you have to go through the terminal and wait longer if your computer doesn't have a dedicated graphics card. It's a good option for a high volume of sensitive content, not for subtitling a Reel between two meetings.

The settings that separate subtitles people read from subtitles people ignore

A subtitle is readable when it fits on two lines max, stays on screen long enough to be read, and doesn't hide behind the app's interface.

Four settings do most of the work.

Reading pace. Professional subtitling standards hover around 17 characters per second and 42 characters per line for a horizontal video. Past that, the eye gives up. AI tools often split too finely or too coarsely: take a look at your longest lines before exporting.

Number of words on screen. In a vertical format, 3 to 5 words per screen with the spoken word highlighted works better than a full sentence. On a long 16:9 video, do the opposite: complete sentences on two lines, easier on the eye.

The safe zone. TikTok, Instagram, and YouTube Shorts layer buttons, a handle, and a caption over the edges. Keep your subtitles between 20% and 70% of the image height, leaning toward the lower middle. A subtitle hidden behind the "Subscribe" button is useless.

Contrast. White text with a black outline, or text on a semi-opaque bar. Avoid bright colors on a light background: it looks lovely on your calibrated screen and is unreadable in full sun on a phone at 30% brightness.

These rules apply to any short-form content, including when you're producing Reels and TikToks with AI in batches.

The typical mistakes of automatic French, and how to fix them fast

French trips models up on four specific points: homophones, liaisons, proper nouns, and numbers.

Proofreading 60 seconds of subtitles takes about two minutes. It's the best investment in the whole chain, because a glaring mistake displayed in big letters in the middle of the screen costs you more credibility than a rough edit.

Your checklist:

• Grammatical homophones: a/à, ces/ses/c'est/s'est, et/est, ou/où, la/là. Models lean on context and get it wrong mostly at the start of a sentence.
• Badly split liaisons: "les enfants ont attendu" can come out as "les enfants nont attendu." Watch for words that start with n' or t' for no reason.
• Proper nouns, brands, and acronyms: your company name rarely lands on the first try. Many tools accept a custom vocabulary list: fill it in once and it serves all your videos.
• Numbers and units: "vingt-neuf euros quatre-vingt-dix" is correct but unreadable as a subtitle. Rewrite it as €29.90. Same logic for percentages and dates.
• Punctuation and capitals: some models return a block with no periods or commas. Add at least the periods, they guide how lines get split.
• Anglicisms: "engagement," "feed," and "prompt" often get transcribed phonetically. Fix them to the spelling your audience expects.

One time-saving trick: proofread the text before you style it. Fixing a word in a text editor takes three seconds; fixing it once the animation is applied takes thirty.

What to take away

If you publish now and then, the subtitles built into TikTok, Instagram, or YouTube Studio are enough and cost nothing. If you're producing several videos a week, go through a specialized tool where transcription, styling, and export all live in one place: what you mainly get back is time on proofreading and multi-platform reposting. Either way, stick to the rule of two minutes of proofreading per minute of video, keep your subtitles out of the interface zones, and cap yourself at two lines. The rest is comfort.

The simplest way to form your own opinion: subtitle a video you've already published, using two different methods, and compare the time it took.