Tools · converter
A video converter that works offline, in the browser
DomeScribe’s converter runs ffmpeg compiled to WebAssembly inside your browser tab, so the conversion happens on your own device: nothing is uploaded, there is no watermark, and once the engine has loaded it keeps working with the network switched off. It converts between MP4, WebM, MOV, AVI, and MKV video and MP3, WAV, FLAC, M4A, OGG, and AAC audio, and the same engine powers DomeScribe’s video compressor, audio compressor, and audio extractor.
Open the converter · Compress a video instead
Updated 2026-08-23
- Engine
- ffmpeg compiled to WebAssembly, running in your browser — no server, no install
- Video formats
- MP4, WebM, MOV, AVI, MKV
- Audio formats
- MP3, WAV, FLAC, M4A, OGG, AAC
- Offline
- After the engine loads once, conversion works without a network connection
- Upload / watermark
- None. The file never leaves your device; the output has no watermark
- Large files
- Depend on your device’s memory; most phone and camera recordings convert as-is
How to convert a video offline in the browser
Open the converter while online
Load /converter once. The first visit fetches the WebAssembly media engine (about 30 MB); your browser caches it. No account is needed for the converter.
Go offline if you want to
Switch to airplane mode or unplug — the engine is already in the tab. This is also the simplest way to confirm for yourself that nothing is being uploaded.
Drop in the file and choose the target
Pick a video output (MP4, WebM, MOV, AVI, MKV) or an audio output (MP3, WAV, FLAC, M4A, OGG, AAC). Choosing an audio format from a video input extracts the audio track.
Convert and download
The conversion runs on your processor; progress shows in the tab. When it finishes, the file is saved from the browser directly to your device — there was never a server copy.
Why a browser converter can work offline
Most online converters are a web form in front of a server: you upload, the server converts, you download. DomeScribe’s converter is built differently. ffmpeg — the open-source media engine behind most video software — is compiled to WebAssembly, a binary format browsers can execute at near-native speed, and loaded into your tab. Once that download has happened once, the whole pipeline (reading the file, decoding, re-encoding, writing the output) runs on your device. The network is only needed to fetch the page and the engine; after that, airplane mode changes nothing.
The practical consequences are the ones people search for: no upload wait for a multi-gigabyte file, no server retention policy to read, no watermark, no queue, and a conversion that finishes as fast as your processor allows. The trade-off is equally direct — speed depends on your machine, and very large files depend on how much memory the browser can give the tab.
Formats it handles
Video in and out: MP4, WebM, MOV, AVI, and MKV. Audio in and out: MP3, WAV, FLAC, M4A, OGG, and AAC. Any video input can be converted to any audio output, which pulls the soundtrack out of a recording — useful for turning a lecture MP4 into an MP3 or a podcast video into the audio file you publish. FLAC and WAV are lossless; MP3, M4A, OGG, and AAC are compressed and much smaller.
- MOV from an iPhone → MP4 for an upload form that rejects MOV
- MKV from a screen recorder → MP4 for an editor that won’t open MKV
- WebM from a browser recording → MP4 for a phone
- MP4 lecture → MP3 for listening; MP4 podcast → WAV or FLAC for editing
Large files, memory, and what to expect
Because the conversion runs inside a browser tab, the practical ceiling on file size is your device’s memory rather than a plan limit. Most phone videos, camera recordings, and screen captures convert as-is on a recent laptop or desktop. Multi-gigabyte files can work but depend on the machine; if a very large conversion stalls, compressing the video first (also in the browser, at /compress-video) or extracting just the audio track reduces the amount of data the engine has to hold. A current Chrome, Edge, Safari, or Firefox on a desktop gives the most headroom; phones have less memory to spare.
The same engine, three more tools
The converter shares its WebAssembly engine with DomeScribe’s other media tools, and all of them share its privacy properties. Compress video shrinks MP4, WebM, MOV, AVI, or MKV with Small, Balanced, and High Quality presets. Compress audio re-encodes MP3, WAV, FLAC, M4A, or OGG to a bitrate you choose. Extract audio pulls MP3, M4A, FLAC, or WAV out of a video you upload. In each case the file stays on your device and the output has no watermark. Once the engine is loaded, they too run offline.
Where the offline rule stops
Only the media tools are browser-local. Transcription — turning speech into text — runs on DomeScribe’s servers because the speech-recognition model is larger than a tab can run well; the recording is uploaded, transcribed, and the original deleted after, with the transcript encrypted and removed after 30 days. So a workflow like “convert offline, then transcribe” crosses from device to server at the second step, and the app says so. The full per-feature account is in the guide on how DomeScribe handles your files.
Questions, answered
Does DomeScribe’s video converter really work offline?
Yes, once the page and its WebAssembly media engine have loaded. The engine (ffmpeg compiled to WebAssembly) runs inside your browser tab, so after the first load you can switch the network off and still convert; nothing needs a server. Open /converter while online first.
Is my video uploaded when I convert it?
No. Decoding and encoding happen on your device inside the browser; the file never leaves it, and the output is saved from the browser directly to your disk. There is no server copy to store or delete.
What formats can it convert?
Video: MP4, WebM, MOV, AVI, MKV. Audio: MP3, WAV, FLAC, M4A, OGG, AAC. A video input can be converted to any audio output, which extracts the soundtrack.
Is there a watermark or a file-size limit?
No watermark. There is no fixed size limit; how large a file you can convert depends on your device’s memory, since the conversion runs inside the browser tab. Most phone and camera recordings convert as-is; for very large files, compress or extract audio first.
Do I need to install anything or create an account?
No install — it is a web page. The converter does not require an account; you can open /converter and convert a file straight away.
Can it convert MOV to MP4, or MKV to MP4?
Yes — both, in the browser. Drop in the MOV or MKV, choose MP4 as the output, and download the result. The same applies to WebM and AVI.
Is the video compressor offline too?
Yes. The video compressor, audio compressor, and audio extractor use the same WebAssembly engine as the converter, so once loaded they run on your device without a network connection, with no upload and no watermark. Transcription is the one DomeScribe feature that runs on a server.
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