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動画ツール

ffmpeg.wasm でブラウザ内の動画を編集 — 完全オフライン、アップロード不要。

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動画ツール

Why browser-only video tools?

Traditional online video tools require you to upload your video to a remote server. That means your footage — whether it is a private recording, a confidential interview, or an unreleased production — is transmitted to and temporarily stored by a third party. The tools on this page use ffmpeg.wasm, a WebAssembly port of FFmpeg, to process video entirely inside your browser. Nothing leaves your device.

ffmpeg.wasm provides the same powerful codec support as native FFmpeg: H.264, VP8, VP9, GIF encoding, audio extraction, and more. The trade-off is speed — WebAssembly runs roughly 5–20× slower than native FFmpeg. For everyday tasks like trimming a clip, muting a video, or extracting a thumbnail, this difference is barely noticeable. For longer re-encode operations such as compression or format conversion, expect to wait a few minutes for a large file.

Choosing the right tool

To cut a video to a shorter length, use the Video Trimmer — it copies streams without re-encoding, so it is near-instant. To reduce file size, use the Video Compressor with a higher CRF value. To share a looping clip on social media, use Video to GIF. To silence a video before posting, use the Video Muter. To fix the orientation of a phone recording, use the Video Rotator. To grab a cover image from a video, use the Thumbnail Generator.

Related audio tools: Audio Trimmer · Audio Converter · Audio Merger

よくある質問

Are my video files uploaded to a server?
No. Every video tool on this page runs entirely inside your browser using ffmpeg.wasm — a WebAssembly build of FFmpeg. Your files never leave your device, not even temporarily.
Why is the first load slow?
ffmpeg.wasm downloads approximately 25 MB of WebAssembly code on the first visit. Subsequent visits are instant because the browser caches the WASM binary. We show a progress indicator so you know the download is in progress.
Which input video formats are supported?
ffmpeg.wasm supports most common formats: MP4 (H.264, H.265), WebM (VP8, VP9), MOV, AVI, MKV, and more. MP4 and WebM work most reliably across all tools.
What format is the output?
Most tools output MP4 (H.264) for maximum compatibility. The GIF tool outputs an animated GIF, the frame extractor outputs PNG images in a ZIP, and the audio extractor can output MP3 or WAV.
Do these tools work on iPhone and Android?
Yes. All tools are mobile-first and work in Chrome and Firefox on Android. iPhone Safari support depends on the iOS version — iOS 16.4+ has sufficient WebAssembly support for ffmpeg.wasm.
How large a video can I process?
The video is loaded into browser memory before processing. Most devices handle files up to a few hundred MB comfortably. Very large files (over 1 GB) may hit RAM limits on mobile devices.
How fast is video processing?
ffmpeg.wasm is single-threaded WebAssembly and runs roughly 5–20× slower than native FFmpeg. A 1-minute MP4 trim takes a few seconds; a full compress re-encode may take a minute or two. Operations that copy streams (trim, mute) are near-instant.
Do the tools work offline?
Yes, after the page and the ffmpeg.wasm core have loaded. The WASM binary is cached by the browser, so once you have visited and loaded a tool, it works without a network connection.
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