Add Subtitles to Video Automatically

What you need first

• A Google sign-in. AI subtitles spend credits, so the editor asks you to sign in before the run starts. Editing and rendering afterwards stay free.
• Enough credits: 1 per minute of video, counted in whole minutes and rounded up, with a 5-credit minimum. New accounts receive 100 free credits at sign-up, and registered accounts get 10 more every day.
• A video no longer than 2 hours, in MP4, MOV, M4V, WebM or MKV.
• No other AI job running on your account. A transcription, translation or dub you started elsewhere on mydubly counts, because only one runs at a time.
• For the finished MP4, a desktop browser that can render: Chrome or Edge 94+, Safari 16.4+ or Firefox 130+.

Run the automatic subtitles

1. In the editor, before choosing a file, check that "Write the subtitles automatically with AI" is ticked.
2. Set "Subtitle language". Leave it on "Same as spoken (auto-detect)" for subtitles in the language people speak, or pick one under "Translate into".
3. Choose the video or drop it on the box. The run begins as soon as the video has loaded.
4. If you aren't signed in, the sign-in window opens; once you're in, the subtitles start without another click.
5. Follow the progress strip through its stages. Stop cancels the run.
6. When it finishes, a note reports how many lines the AI wrote and which spoken language it found, and the lines fill the list and the timeline.

If the video is already open

Perhaps you loaded the video with the switch off, or imported a file you now want to replace. Click AI subtitles in the bar above the preview to open a compact panel with the language menu and a button that shows this video's price before you press it. The label tells you where you stand: "Sign in to generate" when signed out, "Add credits" when the balance is short (it opens the top-up dialog), "Generate subtitles" on an empty video, and "Replace with AI subtitles" when lines already exist. Replacing asks for confirmation, so typed work isn't overwritten by accident.

The same panel holds "Hide subtitles already in the video", which blurs a band of the frame where old burned-in text sits so the new lines can be drawn over it. It blurs rather than erases; hiding hardcoded subtitles explains how to size and place the band.

What happens during the run

Each label in the progress strip is a real step:

Reading the audio

Your browser pulls the soundtrack out of the video file and compresses it. The picture stays where it is.

Sending the audio

Only that compressed audio goes to mydubly's server, over HTTPS.

Detecting the language and writing subtitles

Whisper (large-v3-turbo) identifies the spoken language and transcribes the speech with timestamps.

Translating

Shown only when you picked a target language; the transcript is translated into it.

Timing the lines

The text is cut into short single-line captions of roughly 32 characters (about 12 for Chinese, Japanese and Korean), each on screen for up to about 2.6 seconds and starting on the first spoken word of its phrase.

The server deletes the audio and the text within 30 minutes of delivering the result. Because the video file never left your computer, the render afterwards happens locally, just as it would for typed subtitles.

One difference matters for translated runs. Subtitles in the spoken language are timed from word-level timestamps, while translated ones are divided by text length, so each translated line's timing is approximate. Expect to nudge a few edges on the timeline.

What a run costs

Credits are charged per started minute of video, and 1,000 credits are worth one US dollar.

You pay per run, not per video, so asking the AI again on the same file costs again. Changing styles, editing lines and rendering as often as you like costs nothing. The 100 credits a new account starts with cover an hour and forty minutes of video. Top-ups are paid in rupees; current rates are on pricing.

Check these before you render

Automatic subtitles are a draft. A short review in this order catches most problems:

• The detected language, shown beside the file name as "Spoken: …". If it's wrong, the whole draft will be too; videos that switch between languages are the usual cause, and mixed-language videos explains why.
• Names, brands, product terms and numbers. Recognition guesses at words it hasn't heard often, so scan for them first.
• Stretches with music, laughter or people talking over each other, where words get missed or invented. Replay them at 0.75× speed.
• Line length. The live style shows one short line at a time; if you prefer fuller sentences, Merge joins a line with the next, and Split cuts the selected one at the playhead. Splitting and merging subtitles shows when each helps.
• Warnings in the line list, such as lines too fast to read or overlapping their neighbours.
• Anything that isn't speech. The AI adds no speaker labels and no [music] or [laughs]; if viewers can't hear the audio, add those by hand as described in adding captions.

For a longer routine, fixing auto-generated subtitles works through the common errors one by one.

When the run stops early

• "No speech was found in this video" means the AI had nothing to transcribe: the soundtrack is music only, silent, or the voice is very faint. Check the preview plays audible speech; for music-only clips, type the lines instead.
• A video over 2 hours is refused before any audio is sent. Split it into parts (splitting a video file shows how) and subtitle each one.
• "Another job is still running" means a transcription or dub you started on mydubly hasn't finished. Wait for it, then try again.
• The button reads Add credits: top up, or wait for the next day's free credits.
• You closed the sign-in window: click AI subtitles and press the button again.

Other ways to the same result

If you only want a subtitle file and no video, the AI subtitle generator produces SRT and VTT downloads directly, and translated subtitles does the same in another language. When the wording has to match a script exactly, or there are only a few lines, typing them by hand costs nothing and needs no account. And the auto subtitle generator page treats automatic generation as a tool in its own right.

About the subtitle editor on this page

Opens

MP4, MOV, M4V, WebM, MKV videos your browser can decode

Subtitles from

AI (from the speech, optionally translated into one of 21 languages), an SRT or VTT file, or typing them in

You download

An MP4 with the subtitles drawn into the picture at the original resolution and frame rate, plus SRT and VTT files

Cost

Editing, styling, rendering and SRT/VTT export are free, with no account and no watermark. AI subtitles cost 1 credit per minute (5-credit minimum per video); signing in with Google gives 100 free credits and accounts get 10 free credits a day

Privacy

The video never leaves your device and is rendered in your browser. Only for AI subtitles is the audio sent, over HTTPS, and it is deleted within 30 minutes of delivery

Rendering needs

Chrome or Edge 94+, Safari 16.4+, or Firefox 130+ on a computer. Editing and SRT/VTT export work in any current browser