Convert Video to MP4 Free Online
Convert any video to MP4 (H.264 + AAC) for free in your browser. Fast in-browser remuxing or transcoding with no upload. Your files stay on your device.
How to Convert Your Video to MP4 Online
- Choose your video: Drop a WebM, MKV, MOV, FLV, AVI, or another video file into the converter, or select it from your device.
- Start the MP4 conversion: Click convert and GrepCut transcodes the video to an MP4 file with H.264 video and AAC audio inside your browser.
- Save the new MP4: Download the finished MP4 to your device and use it in players, editors, websites, chat apps, or social platforms.
Your media stays local. The conversion runs in your browser, so your file is not uploaded to a server.
Why Your Video May Need an MP4 Version
A file extension does not tell the whole story. MP4, MKV, MOV, WebM, AVI, and FLV are containers, while H.264, VP9, HEVC, AAC, Opus, and similar names are codecs inside those containers. If an app rejects your file, the container, the codec, or both may be the reason.
If your WebM plays in Chrome but fails on an iPhone, or your MOV from a phone will not embed cleanly on a website, converting the file to H.264 + AAC MP4 gives you the safest practical playback target. It does not make every old device perfect, but it avoids the most common compatibility trap: a familiar file name with unsupported video or audio inside.
GrepCut is useful when you want a shareable MP4 without sending private footage to a remote converter. You can handle screen recordings, exports from editing apps, camera clips, and downloaded video files directly on your device.
The goal is not to create a magic format. The goal is to give your file the MP4 container and codec combination that browsers and devices are most likely to understand.
What Happens When You Convert Common Video Files
| Your source file | What may go wrong | What GrepCut creates |
|---|---|---|
| WebM | It may play in one browser but fail in Safari, Photos, older mobile apps, or upload forms. | An MP4 with H.264 video and AAC audio for wider playback. |
| MKV | It can contain codecs or audio tracks that some phones, TVs, and editors do not accept. | A standard MP4 output with a simpler codec target. |
| MOV | A phone or camera MOV may work locally but fail in a web player, form upload, or non-Apple app. | An MP4 designed for cross-platform sharing. |
| AVI or FLV | Older containers can be awkward in modern browsers, social apps, and mobile workflows. | A modern MP4 that is easier to preview, upload, and reuse. |
Conversion speed depends on your device, browser, source codec, resolution, bitrate, and video length.
What Changes During MP4 Conversion
When you convert a video to MP4 in GrepCut, the output is not just renamed. Your browser creates a new file using an MP4 container, H.264 video, and AAC audio. That matters because an .mp4 extension alone does not guarantee compatibility.
You may notice that high-resolution files, HEVC clips, or long recordings take longer to process. That is expected because transcoding uses your local CPU rather than a remote server. The tradeoff is privacy: your video does not need to leave your device.
- Container: The final file is packaged as MP4, a common delivery container for video.
- Video: The video stream is encoded as H.264 (AVC), a widely supported playback codec.
- Audio: The audio stream is encoded as AAC for broad device and browser support.
- Location: The conversion runs locally in your browser instead of uploading your file to a server.
When MP4 Conversion Helps You
✓ Advantages
- You need a video that is easier to open on phones, tablets, computers, and TVs
- You want an upload-friendly file for social platforms, websites, or messaging apps
- You have a WebM, MKV, MOV, AVI, or FLV file that one app refuses to play
- You want private browser-side conversion without sending the source file away
✗ Disadvantages
- Transcoding can take time on large 4K, HEVC, high-bitrate, or long videos
- A new encode can slightly change quality compared with the original source
Video to MP4 Converter FAQ
Can you convert WebM, MKV, MOV, AVI, or FLV to MP4?
Will your video file be uploaded?
Why does an MP4 sometimes still fail to play?
Will converting your video to MP4 be lossless?
Why does WebM often need conversion before sharing?
Can you convert a video to MP4 on a phone?
Does the converter remove audio or subtitles?
Convert Your Video to MP4 Privately
Open GrepCut, drop your video, and create a browser-side MP4 with H.264 video and AAC audio. Your file stays on your device while you prepare it for playback, upload, or sharing.
Open GrepCut EditorRelated format converters
- MOV to MP4: Fast remux path for iPhone and Mac QuickTime files
- WebM to MP4: Fix WebM clips that fail on iPhone or older players
- MKV to MP4: Open Matroska files in apps that only accept MP4
- Compress Video: Make the finished MP4 smaller for sharing
- AVI to MP4: Free online AVI to MP4 converter, transcode videos in your browser.
- DAT to MP4: Free online DAT to MP4 converter, transcode VCD video in your browser.
- FLV to MP4: Free online FLV to MP4 converter, transcode Flash video in your browser.
Sources & further reading
- Super User discussion about WebM VP9 to MP4 playback problems
- Stack Overflow discussion about MOV browser support
- Reddit r/ffmpeg discussion about containers and MP4 conversion
- Reddit discussion about MP4 files failing because of codecs
- MDN guide to web video codecs
- Apple guidance for delivering video content in Safari