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Online MP4 Converter

Convert any video to universal H.264 MP4 free, private, in your browser

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100% private. Your file is processed locally in your browser with WebAssembly — it is never uploaded to a server, stored, or seen by anyone.

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The Online MP4 Converter turns almost any video file (MKV, MOV, AVI, WebM, FLV, WMV, M4V, and more) into a universally compatible MP4 encoded with H.264 video and AAC audio. This is the format that plays everywhere, including iPhones, Android phones, Windows, macOS, smart TVs, and platforms like YouTube and Instagram, so a clip that refused to open or upload becomes instantly shareable.

Conversion runs entirely inside your web browser using ffmpeg.wasm, a WebAssembly build of FFmpeg, so your video is decoded and re-encoded on your own device and never uploaded to a server. That makes it ideal for anyone handling private footage, large files, or sensitive recordings who needs a fast, free MP4 converter without installing software, creating an account, or trusting a cloud service.

Why use this tool

Plays and uploads everywhere

H.264/AAC MP4 is the universal format accepted by iPhones, Android, browsers, smart TVs, editors, and social platforms, so converted files just work without compatibility errors.

Completely private by design

Your video is converted on your own device with ffmpeg.wasm and never uploaded, making it safe for confidential recordings, raw footage, and copyrighted material.

No installation or signup

There is nothing to download and no account to create. Open the page, drop in a file, and convert, with no software, watermarks, or hidden paywalls.

Control over size and quality

Adjustable quality, bitrate, resolution, and frame rate let you balance visual fidelity against file size, whether you need a pristine archive copy or a small clip for messaging.

How to use the Online MP4 Converter

  1. Add your video

    Drag and drop your video file onto the page or click to browse and select any format such as MKV, MOV, AVI, or WebM from your device.

  2. Choose a quality or bitrate setting

    Pick a quality preset or set a target bitrate, choosing higher for maximum detail and a larger file, or lower for a smaller, more shareable MP4.

  3. Adjust optional output settings

    Optionally set the resolution or dimensions and frame rate (fps), or keep the source values to match the original video.

  4. Start the conversion

    Click Convert and let ffmpeg.wasm re-encode the video to H.264 and AAC locally in your browser, keeping the tab open until it finishes.

  5. Download your MP4

    When processing completes, download the finished MP4 file straight to your device, ready to play, edit, or upload anywhere.

Popular use cases

  • Convert an MKV or AVI download to MP4 so it finally plays on your iPhone or in the Photos app
  • Turn a screen recording or camera clip into MP4 so a social platform or messaging app stops rejecting the upload
  • Standardize a folder of mixed-format videos into MP4 before importing them into a video editor
  • Re-encode a private or sensitive recording to a shareable MP4 without uploading it to any cloud service

Frequently asked questions

Is the Online MP4 Converter free to use?
Yes, it is completely free with no limits on the number of conversions. There is no signup, no account, no watermark, and no paid tier. Every feature runs in your browser at no cost.
Are my video files uploaded to a server?
No. All conversion happens locally in your browser using ffmpeg.wasm (WebAssembly), so your file never leaves your device and is never uploaded to any server. This makes it safe for private, confidential, or copyrighted footage.
Which video formats can I convert to MP4?
You can convert almost any common video format, including MKV, MOV, AVI, WebM, FLV, WMV, M4V, MPEG, 3GP, OGV, and TS. The output is always a standard MP4 using H.264 video and AAC audio for maximum compatibility across devices and platforms.
Is there a file size limit?
There is no fixed file size cap, but because processing happens in your browser using your device's memory, very large files (typically over a few GB) may run slowly or hit your browser's memory limits. For best results on multi-gigabyte videos, use a desktop browser like Chrome or Edge on a machine with ample RAM.
Will converting to MP4 reduce the video quality?
There is a small quality change because H.264 is a lossy codec and the video is re-encoded, but the tool uses sensible default settings to keep the result visually close to the source. You can choose a higher quality or bitrate setting to preserve more detail at the cost of a larger file, or a lower setting for a smaller file.
How long does conversion take?
Because encoding with libx264 runs on your own device via WebAssembly, speed depends on your CPU, the video's length, and resolution. Short clips finish in seconds to a minute, while long or high-resolution videos take longer than a native desktop app would. The browser tab must stay open while it processes.
Why convert to MP4 with H.264 and AAC instead of another codec?
H.264 video paired with AAC audio in an MP4 container is the most widely supported combination across phones, browsers, editors, and social platforms, so it virtually always plays and uploads without issues. Formats like MKV or AVI often fail on iPhones or social apps, which is exactly the problem this MP4 converter solves.
Can I convert a video that won't play or upload anywhere?
Yes, that is a primary use of this tool. Files in formats like MKV, AVI, FLV, or WMV that refuse to open on an iPhone or get rejected by a social platform can be converted to a standard MP4 that plays and uploads everywhere from any modern browser on desktop or mobile.

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MOV → MP4AVI → MP4MKV → MP4WebM → MP4FLV → MP4WMV → MP4M4V → MP4MPEG → MP4