Replace Video Audio is a free, in-browser video tool. Replace the audio track of any video with a new music or voiceover file. The video stream is preserved — only the audio is swapped. Files are processed entirely in your browser with FFmpeg WebAssembly. The page exposes a small surface — input, controls, output — so a first-time visitor can complete the job without reading documentation.
Internally the tool runs on FFmpeg compiled to WebAssembly — the same processing stack used by professional desktop pipelines, just compiled for the browser. MP4, WebM, MOV, MKV, AVI, FLV, and OGV files are accepted natively. 500 MB is the practical ceiling, set so the tool stays responsive on phones and older laptops.
Most people land on Replace Video Audio via a search at the moment they actually need the tool. That shapes the design: the page is a single screen with the input on one side, the controls in the middle, and the result on the other, so a first-time visitor can complete the job without reading documentation.
The browser sandbox isolates the page's JavaScript from the rest of the system, the same way it isolates every other tab you have open. Replace Video Audio works inside that sandbox: it reads the file you give it, processes it with FFmpeg compiled to WebAssembly, and writes the result back. Nothing leaves the page's memory unless you choose to download or copy it.
On limits: 500 MB per file is the ceiling. Output formats and quality settings are listed in the controls panel above, and they apply to every run.
Replace Video Audio sits in a small group of related tools. Useful neighbours include Add Audio to Video, Mute Video, Video to MP3, and Video Converter. They are designed to compose: the output of one is a sensible input to the next, so a multi-step task is usually a sequence of single-click operations.
Replace Video Audio fits naturally into the workflow of support agents preparing screen recordings and teams compressing demo recordings, both of whom typically need a fast result inside the browser. There is no learning curve to budget for: anyone who has used a typical web upload form can complete a run on the first try.
Output handling is intentionally boring: Replace Video Audio produces `{name}-edited.{ext}` and triggers your browser's standard "save" behaviour. If you have a default download folder configured, that is where it will land. There is no Favtoo-side history of jobs you have run.
Replace Video Audio is honest about scope: it handles a single, well-defined video editing and conversion step. Specialist edge-case work — uncommon formats, very large inputs, or pipelines that need scripting — is what dedicated desktop apps are for. This page handles the common case quickly.
Replace Video Audio is one example of a broader pattern: utility software increasingly works as single-page, client-side experiences. Every page in the catalog is shaped that way, which keeps each tool fast to load and easy to recommend in a single link.
Pro tip: Replace Video Audio works just as well in a private/incognito window as in a normal one, which is occasionally useful when you want zero browser-history footprint of the job. Another tip: if the tool ever feels slow, it is almost always because the browser tab is competing for CPU with another tab — pausing or closing the heavy ones gives the engine room to work.
Replace Video Audio fits the gap where opening a desktop app feels heavy and writing a script feels overkill. The page handles the common video editing and conversion task with sensible defaults so a single visit usually completes the job; for highly specialised work, a dedicated desktop application can offer more knobs to turn.
When something goes wrong, the cause is usually one of three things: a malformed input, a browser that is out of memory, or a corporate proxy that is interfering with the page's static assets. The first two are easy to diagnose; the third typically requires asking your IT team to allow FFmpeg compiled to WebAssembly to load.
That is the whole tool. Use Replace Video Audio for as long as it stays useful to you, and if it does, the catalog has many more tools built the same way. Each applies the same single-purpose discipline, so the way you used this page transfers to the next one you try.
A WebAssembly build of FFmpeg loads in this page and replaces the audio track of your video entirely on your device. The video stream is copied without re-encoding (fast), and the new audio is muxed into a fresh MP4.
Server tools run native multi-threaded FFmpeg. WebAssembly is single-threaded in the browser, typically 2–4× slower for muxing. The trade-off is total privacy: your files never leave your device.
MP3, WAV, AAC, M4A, OGG, and FLAC. The audio is automatically re-encoded to AAC at 192 kbps for the MP4 output, which plays everywhere.
No. The video stream is copied byte-for-byte into the new MP4 container — no re-encoding, no quality loss, and processing is much faster than tools that touch the pixels.
The output is automatically trimmed to the shorter of the two streams. If your new audio is longer, only the first portion is used; if shorter, the trailing video has silence.
Up to 500MB of video and 100MB of audio. Because the video stream is copied without re-encoding, even long videos process quickly.
This tool always removes the original audio and replaces it. Add Audio to Video lets you mix the new track on top of the existing audio (great for background music behind narration).
No. The replacement runs entirely in your browser tab. Nothing is transmitted, stored, or logged. Closing the tab erases the files from memory immediately.
Replace Video Audio is built on FFmpeg compiled to WebAssembly, which is the same class of engine used by professional video editing and conversion pipelines. For deterministic operations, the output is byte-identical to what an equivalent CLI run would produce; for operations involving a codec or a model, the result is well within the range of what comparable tools generate. If you have a specific reference output you need to match, run a small test job first to confirm the configuration produces what you expect.
Replace Video Audio is built to preserve quality wherever the underlying video format allows it. Operations that are mathematically lossless (e.g. structural transformations, lossless re-encoding) round-trip with no perceptible change. Operations that involve a lossy codec inevitably introduce small artefacts at the byte level, but the defaults aim at the sweet spot where output looks or sounds the same to a normal viewer or listener while still being meaningfully smaller or faster than the input.
Desktop apps usually have more advanced features but require installation, maintenance and (often) a licence. Paid online tools are convenient but route your file through their servers and gate downloads behind accounts. Replace Video Audio sits in between: free, instant, and private, but intentionally narrow in scope. For one-off jobs and the common video editing and conversion operations, it is usually the lowest-friction choice; for highly specialised work, a dedicated app is still the right answer.
Failures usually fall into one of three buckets: the input is in an unsupported format, the input is over the size cap, or the input is structurally malformed (a truncated download, a partial export, or a stream the engine does not recognise). The first two are easy to confirm — check that your file is one of MP4, WebM, MOV, MKV, AVI, FLV, and OGV and that it is below 500 MB. For the third, opening the file in its native viewer first is the fastest way to confirm the source is intact.
Replace Video Audio runs in any modern mobile browser — Safari, Chrome, Firefox and the in-app browsers in most messaging apps all support the underlying APIs. Performance depends on the device: a recent phone handles typical inputs nearly as fast as a laptop, while older devices may take a few seconds longer near the 500 MB ceiling. The interface lays out cleanly on small screens, so you do not need to pinch-zoom to see the controls.
Replace Video Audio is updated whenever the underlying engine releases an improvement or a bug fix. Because the tool is delivered as a static page, every visit fetches the latest version automatically — there is no "version" to manage on your end. If a particular release ever changes default behaviour, the change is documented on Favtoo's changelog so you can confirm what shifted.
Replace Video Audio is free to use. The processing runs in your browser, which keeps the per-user cost low enough that the tool can be offered openly. The download is the same file the engine produced — you can use it for as many runs as you need.
Replace Video Audio uses native HTML controls wherever possible, which means keyboard navigation, focus rings, and screen-reader labels work the way the platform expects. The drop zone accepts files via the keyboard-accessible file picker as well as drag-and-drop, and result downloads use standard browser download flows. If you spot an accessibility gap, Favtoo treats it as a bug worth fixing.
Your file is processed inside your browser by FFmpeg compiled to WebAssembly. The engine reads the file's bytes from your tab's memory, computes the result, and writes the result back into the tab. You can confirm what the page does by opening developer tools and watching the Network tab during a run — the requests you see are for the tool's static assets only.
Video to GIF
Convert any video clip to an animated GIF entirely in your browser. Pick the start, length, frame rate, and width — your file is processed locally with FFmpeg WebAssembly and never uploaded.
Screen Recorder
Record your screen, a window, or a browser tab directly in your browser. Optionally include system audio and your microphone. Capture, preview, and download the video without installing any app — and without uploading anything.
Webcam Recorder
Record your webcam directly in your browser with optional microphone audio. Pick the resolution (480p, 720p, or 1080p), frame rate, and mirror mode, then capture and download the result without installing any app.
Screen + Webcam Recorder
Record your screen with your webcam composited into a picture-in-picture corner — perfect for tutorials, course videos, demos, and reaction recordings. Pick the camera position, size, and audio sources, then capture and download in your browser.
Video Slideshow Maker
Turn a stack of photos into an MP4 slideshow with per-slide durations, crossfades, and an optional soundtrack. Pick the resolution (up to 1080p), frame rate, and transitions, then download a single MP4 — all processed in your browser with FFmpeg WebAssembly.
Video from Images + Audio
Combine a stack of photos with a music track or narration into a single MP4 video. Pick the resolution, per-slide duration, transitions, and let the slideshow length match the audio. All processed in your browser with FFmpeg WebAssembly.
Video Trimmer
Set precise in and out timestamps, snap to keyframes when needed, and document handles for social-safe cutdowns.
Video Splitter
Split any video into 2–10 equal-length pieces, packaged as a downloadable ZIP. Files are processed entirely in your browser with FFmpeg WebAssembly using lossless stream-copy.