Trimming, Converting, and Extracting Audio From Video — What FFmpeg.wasm Can Do in Your Browser

Video editing has traditionally meant either installing a heavyweight desktop app or uploading a file to a cloud service and waiting for it to come back. Neither is great for a quick job — trim ten seconds off a screen recording, pull the audio out of an interview, convert a file so it'll actually play on the device you're sending it to. FFmpeg, compiled to WebAssembly, makes it possible to do all three directly in a browser tab, with the file never leaving your device. It's worth knowing exactly what that setup can and can't do before you rely on it.

What's actually running under the hood

Video Trim, Video Transcoder, and Extract Audio all run on the same engine: FFmpeg compiled to WebAssembly, executing in your browser rather than on a server. This is the real FFmpeg — the same encoder/decoder logic that powers a huge share of video software — not a simplified reimplementation. The trade-off is that it runs on the single-threaded WebAssembly build, so it doesn't spread work across your CPU's cores the way a native desktop app with multi-threaded encoding would. For a short clip or a typical screen recording, that's not noticeable. For a long, high-resolution file, expect it to take meaningfully longer than the same job would on dedicated desktop software.

Trimming and cropping

Video Trim cuts a clip to a specific start and end time, with an optional pixel-precise crop (width, height, X, Y offset) applied at the same time. The output is always exported as MP4 regardless of your source format — there's no format picker in trim mode, since the tool is scoped specifically to "cut this section out," not general conversion.

Converting between formats

Video Transcoder handles the broader conversion job: MP4, MOV, AVI, GIF, and MP3 as outputs, with WebM accepted as an input format but not currently available as an output. It uses FFmpeg's default encoder settings for each target format — there's no manual bitrate, resolution, or quality slider today, so the resulting file size follows your source footage's own characteristics rather than a target you set. If you specifically need a smaller file, trimming length or resolution before conversion has more effect than anything adjustable in the converter itself.

Pulling just the audio out

Extract Audio strips the audio track from a video file and exports it as an MP3 — the only output format this specific tool supports today. If you need a different audio format (WAV, AAC, FLAC), that's not available in this tool; MP3 covers the overwhelmingly common case (attaching audio to an email, importing into a podcast editor, archiving a recording) but isn't universal.

Making a GIF

GIF Maker uses the same FFmpeg.wasm engine to convert a video clip into a looping GIF — useful for a bug report, a quick product demo, or dropping a short clip straight into a chat thread without anyone needing to click play. Like the transcoder, it uses FFmpeg's default settings rather than exposing a palette/dithering quality control, so a highly detailed source clip may produce a larger GIF than a tool built specifically to optimize GIF palettes would.

When this setup is and isn't the right call

For a screen recording, a short clip, or a typical smartphone video, all four of these tools handle the job in the time it takes to drag the file in and click a button — with the added benefit that footage you'd rather not upload anywhere (an unreleased demo, an internal recording, anything under an NDA) never has to leave your device. For a multi-minute 4K file, or a batch of many files at once, the single-threaded processing model means you're trading some speed for not needing to install anything or wait on an upload — a reasonable trade for an occasional job, less so if this is a daily, high-volume workflow, where dedicated desktop software with real multi-core encoding will still be faster.

The Bottom Line

Browser-based video processing via FFmpeg.wasm is genuinely the same underlying encoder software running locally, not a lightweight substitute — the honest trade-off is processing speed on longer files, not capability or quality on the operations it supports. For the common cases (trim a clip, convert a format, pull out the audio, make a quick GIF), that trade-off is easy to accept in exchange for never uploading the file anywhere.