MP4 Converter
FileFlip converts MP4 files into 30 other formats entirely inside your browser, using WebCodecs and FFmpeg compiled to WebAssembly. The MP4 file is never uploaded to a server: it is read off your disk, converted on your own machine, and saved back by the browser. There is no file-size limit and no account to create.
How do I convert an MP4 file?#
- Drop your MP4 file onto the converter at the top of this page, or click it to pick one from your computer.
- Choose the format you want out of it. FileFlip downloads the engine that conversion needs, once, and your browser caches it.
- Conversion starts the moment you pick the format, and the result is yours to download. The work happens in this tab, so nothing is uploaded and nothing is queued.
Is it safe to convert MP4 files online?#
Yes, because nothing is uploaded. FileFlip converts MP4 files inside the browser tab you already have open, using WebAssembly builds of the same engines a desktop converter would install. Your file is read from your own disk into the page's memory, and no request carrying it is ever made.
You do not have to take that on trust. Open your browser's network panel, run a conversion, and you will see the engine come down and your file go nowhere. There is no upload, no server-side copy, no retention window, and no account tied to what you converted.
How FileFlip works lists every engine, its version and its download size, and shows how to check for yourself that nothing leaves your machine.
What happens to a MP4 file#
FileFlip converts MP4 into 30 formats with WebCodecs and FFmpeg, all of it inside the browser tab. Each conversion below names the engine it uses, what it downloads, and exactly what that conversion keeps or drops.
| Category | Video Files |
|---|---|
| File extension | .mp4 |
| FileFlip support | Read and written |
| Conversions available | 30 |
| Engines | WebCodecs and FFmpeg |
| Downloaded to your browser | 30.8 MB on the first conversion, then cached |
What is an MP4 file?#
An MP4 file holds video, audio, subtitle and chapter tracks together in the MPEG-4 Part 14 container, the structure ISO standardised from Apple's QuickTime format and the way most video is stored and shared today.
Choose MP4 when the file has to play somewhere you do not control, which covers anything uploaded, emailed or handed to another person.
Convert an MP4 to something else when the destination is not a player: pulling out the audio, making a GIF, or moving into Matroska to keep several subtitle and audio tracks in one file.
The MP4 file format reference covers the specification, the programs that open one, and what each conversion keeps or drops.
MP4 questions people ask#
Is MP4 a video format or a codec?
MP4 is a container, not a codec. It is a wrapper holding video, audio and subtitle streams side by side, and the codec inside decides whether a device can actually decode it. Two MP4 files can behave completely differently: one holding H.264 plays everywhere, one holding H.265 or AV1 may not play at all on older hardware.
Why won't my MP4 file play?
An MP4 that refuses to play is almost always carrying a codec the player cannot decode rather than being damaged. H.265 and AV1 are the usual culprits, since both need recent hardware or software support, and some MP4s from streaming services are encrypted and will only open in an authorised app. Re-encoding the video to H.264 fixes nearly all of these.
Does converting MKV to MP4 lose quality?
Converting MKV to MP4 loses nothing at all when the video is already H.264 or H.265 with AAC audio, because the streams are lifted out of one container and dropped into the other untouched. That is a remux, and it runs at disk speed. Quality only drops when the codec has to change, for example a VP9 video that MP4 players do not expect, which forces a full re-encode.
What is the difference between MP4 and MOV?
MP4 was standardised from Apple's QuickTime file format, which is what a MOV file uses, so the two share the same underlying atom structure. In practice this means an H.264 video in a MOV and the same video in an MP4 are the same bytes in a slightly different wrapper, and converting between them is a fast remux rather than a re-encode. MOV also carries codecs MP4 does not, ProRes being the common one.
Does MP4 support subtitles and chapters?
MP4 carries both, subtitles as timed text tracks and chapters as a chapter track, but player support is uneven. QuickTime and VLC read them, plenty of smart TVs and browsers ignore them, and many encoders never write chapters in the first place. Subtitles delivered as a separate SRT file alongside the MP4 are more reliably picked up.