Add Subtitles Without Uploading the Video

The two modes side by side

The editor has two ways of getting subtitle text, and they differ in exactly one respect: whether the soundtrack leaves your computer.

The video file

Without AI: read by your browser from where it sits on your disk. With AI: the same; the picture is never extracted or sent.

The soundtrack

Without AI: stays on your computer. With AI: decoded, compressed and sent to mydubly's server over HTTPS.

The subtitle text

Without AI: typed or imported by you, held in the browser. With AI: written on the server from the audio, then sent back to the browser.

The rendered MP4

In both modes, encoded on your computer and saved through your browser's download.

Your identity

Without AI: no account involved. With AI: a Google sign-in and a job record in your account.

If the picture is the sensitive part (faces, screens, documents, an unreleased product), either mode keeps it local. If what people say is the sensitive part, only the mode without AI keeps the words local too.

What the AI step sends, exactly

When AI subtitles are on, this is the full sequence:

1. Your browser decodes the video's audio track into mono sound at 16 kHz, the rate speech recognition works at. The picture isn't read for this.
2. The sound is cut into chunks, and each chunk is compressed to Opus where your browser supports that, roughly an eighth of the raw size, or packed as WAV where it doesn't.
3. The chunks go to mydubly's server over HTTPS, several at a time, together with the file name, the video's length and the subtitle language you chose.
4. The server transcribes them with Whisper, translates the text if you asked for another language, and returns timed subtitles.
5. As soon as your browser has the result, it asks the server to delete its copy. Anything left behind, including from failed or cancelled jobs, is removed within 30 minutes.
6. Your account keeps a job record: file name, length, languages, status and credits charged. It doesn't keep the audio or the text.

mydubly's privacy policy also says audio and text aren't used to train models. Transport is protected by HTTPS; the site makes no other security or compliance claims, so if your organisation has rules about where recordings may be processed, check them against this list. The private video translation page describes the same server side for translation and dubbing jobs, and how cloud speech processing handles privacy puts it in wider context.

What stays in your browser

Even with AI off, some things are stored on your computer while you work, and it helps to know where:

• The video. The browser reads the file from your disk for as long as the tab is open. No copy of it is saved by the editor.
• The draft. Your lines, style and blur-band settings are saved in this browser's local storage, with the file's name, size and modified date so the editor can recognise the video next time. Up to five drafts are kept; "Start new video" after a download deletes that video's draft.
• The render. Long renders are written to the browser's private storage on your disk before the download is handed over, and that copy is cleared the next time you render, start a new video or reopen the editor.
• Your downloads. The MP4 and any SRT or VTT exports go wherever your browser saves downloads.

On a shared computer, clear the site's data in the browser settings when you're done.

What the network still carries

This is a web page, not an offline app. The editor's code and its fonts load from the internet, which is why you need a connection to start. Visitors who haven't bought credits also see ads from Adsterra, loaded in a sandboxed frame that can't read your files or the page. None of those requests carries your video. If you need a tool for a machine with no internet connection at all, desktop software is the answer: a subtitle editor such as Subtitle Edit or Aegisub for the text, and HandBrake or FFmpeg for burning the subtitles in.

How other approaches handle your file

There are broadly four ways to subtitle a video, and each places the file differently:

• Upload-based online editors send the whole video to their servers, transcribe and render there, and give you a download. Convenient across devices, and the heavy lifting isn't on your computer, but the full video leaves your hands, and retention terms vary by service.
• Desktop programs keep everything local, including speech recognition if you add a local model. You install and maintain them, and speed depends on your hardware; running Whisper locally shows what that involves.
• Some browser tools run speech recognition inside the tab, so the audio stays too. Expect a large model download and transcription speed tied to your device.
• This editor keeps the video and the render on your computer and sends only the audio, and only when you ask for AI subtitles.

None of these is right for every job. Client-side versus server-side processing compares the trade-offs in more depth.

Picking a mode for sensitive footage

For the typing workflow, see adding subtitles by hand. If the same work happens on a computer where you can't install anything, subtitling without installing software covers the browser requirements, and subtitling without an account explains which steps never ask you to sign in. When you do want AI, the AI subtitle generator handles audio the same way: the video stays put, the soundtrack goes.

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