Add captions to your video without uploading it
CapStudio transcribes, styles, and exports your captioned MP4 entirely in your browser. Not "encrypted in transit", not "deleted after processing": your footage never leaves your machine in the first place.
Free to start. No signup, no account, no upload.
Every cloud caption tool starts with an upload
Upload the clip, wait for the progress bar, wait for their queue, download the result. Along the way your raw, unpublished footage lands on someone else's servers under someone else's retention policy. For a holiday clip that might not matter. For client work under NDA, an unreleased product, or footage of your kids, it does.
The upload is not there for your benefit. It exists because the transcription and rendering run on the vendor's hardware, which also means metered exports and per-minute pricing. CapStudio removes the reason: your machine does the work, so there is nothing to upload, nothing to queue for, and nothing for us to meter.
How captions happen without an upload
Transcription runs in the tab
OpenAI's Whisper model runs inside your browser on WebGPU (or WASM as a fallback). The model downloads once, caches, and turns your audio into word-timed text without the audio going anywhere.
Styling renders on a canvas
Every caption style is drawn on a canvas on your machine. The live preview and the final export share the same render path, so what you see is what you get.
The MP4 encodes on your device
WebCodecs, the browser's built-in video encoder, burns the captions into a new MP4 and carries your original audio over. The file goes straight to your downloads folder.
Exactly what leaves your browser
"Private" claims deserve specifics. Here is the complete list.
- Your video and audioStays local
- Never leave your device. There is no upload step anywhere in the app.
- Your transcript and style settingsStays local
- Stay on your device. If you turn on Pro cloud sync, a small project file (text and settings, not media) syncs so you can resume on another machine.
- Sign-in and billingOptional
- Standard Google sign-in and Stripe checkout, only if you create an account or upgrade. You can caption without an account.
- Anonymous analyticsOptional
- A cookieless, anonymous event when an export finishes (which style was used). Never the video, never the transcript.
Don't take our word for it: open your browser's developer tools, watch the Network tab, and export a clip. The absence of an upload is the product.
Who this matters for
Agencies captioning client footage under NDA. Podcasters handling a guest's appearance. Anyone captioning pre-launch product video, legal or medical material, or family clips. If the footage should not sit on a stranger's server, the safest upload policy is no upload at all. See how CapStudio compares to cloud tools like Submagic and VEED, or browse the caption styles.
Questions
How can it transcribe my video without a server?
CapStudio runs the Whisper speech-recognition model inside your browser using WebGPU, with a WASM fallback for machines without GPU access. The model file downloads once from a public CDN and is cached; your audio is processed locally and never transmitted.
Is the no-upload claim actually verifiable?
Yes. Open your browser's developer tools, watch the Network tab, and caption a clip. You will see the model download and small app requests, and no request carrying your video or audio anywhere.
Does it work offline?
CapStudio is a website, so you need a connection to open it and to download the AI model on first use. After that, the transcription and export themselves run locally; the work does not depend on our servers.
Which browsers does it work in?
Chrome and Edge are best because of WebGPU acceleration. Firefox works with a slower fallback. There is no mobile support yet.
What does it cost?
The free tier is permanent: caption and export with a small watermark, no account needed to try it. Pro at $9/mo (or $59/yr) removes the watermark, unlocks every style, and runs a larger, more accurate model.
Caption your next clip without the upload
Drop in a clip, transcribe it, pick a style, export. Free to start, and your footage stays exactly where it is now.