Re-encode VP8, VP9 or AV1 WebM clips into an H.264 and AAC MP4 that iPhones, Macs, TVs and editing apps accept. Nothing is uploaded, and there’s no account, watermark or limit.
Drop one or more recordings where the page says “Drop WebM files here”, or tap to choose them. Each row lists the duration and resolution and announces the work ahead, typically “VP9 video will be re-encoded to H.264 (slower)”.
Press “Convert 1 video to MP4” (the count updates as you add files). Clips are encoded one after another, each with its own percentage and a Cancel button.
When a row is finished, press Download to save that MP4, or “Download all (.zip)” to collect several at once.
WebM is an open, royalty-free video format that Google launched in 2010 for the web. Its container is a trimmed-down version of Matroska (the MKV format), and it only allows royalty-free codecs: VP8, VP9 or AV1 for the picture, Vorbis or Opus for the sound. Chrome, Firefox and Edge play it natively, and YouTube uses VP9 heavily.
You usually end up with a WebM because something in a browser made it. Screen recorders that run in a web page, video calls saved through the MediaRecorder API, OBS set to a custom WebM output, and clips saved from websites are common sources. Those files play fine in a browser but stall elsewhere: the iPhone Photos app won't import them, QuickTime Player won't open them, and many TVs and editing apps refuse them.
Unlike MOV or MKV, a WebM can never simply be copied into a widely playable MP4. Players such as QuickTime, iOS and most TVs expect H.264 or HEVC video with AAC sound in an MP4, not VP9 and Opus. So filetidy decodes every frame and encodes it again as H.264, and turns Opus or Vorbis into AAC at 160 kbit/s. Resolution and frame rate stay the same.
VP8 and VP9 can carry a transparent background (an alpha channel), used for overlays and stickers. H.264 MP4 has no alpha channel, so the converted file is fully opaque: transparent areas do not stay see-through.
Windows
That VLC profile stores the sound as MP3 inside the MP4. Most players accept it, but some editors and phones prefer AAC.
Mac
QuickTime Player can't open WebM at all, which is why Mac users usually need a converter.
Keep the WebM if the clip will only be played in a browser or embedded on a website: VP9 and AV1 give a good picture at small sizes and all major browsers support them. There is no point re-encoding a file that already plays where it's needed, since every re-encode loses a little detail.
Choose MP4 when the video has to leave the browser: sent to an iPhone, dropped into iMovie, Premiere or a slideshow, played on a TV from a USB stick, or attached to a form that only accepts MP4. H.264 in MP4 is the most widely supported video file there is.
Plan for time. Because every frame is decoded and re-encoded, a WebM conversion is far slower than a MOV or MKV remux. On a recent laptop with hardware encoding, a few minutes of 1080p usually converts in about the time it takes to play, or faster; long 4K recordings or older phones take noticeably longer. The MP4 may also be larger than the WebM, since VP9 and AV1 are more efficient than H.264.
Because the codecs inside a WebM (VP8, VP9 or AV1 and Opus or Vorbis) are not what MP4 players expect. Putting VP9 into an .mp4 file would technically work in some browsers, but the iPhone Photos app, QuickTime and most TVs would still refuse it. Re-encoding to H.264 and AAC is what makes the result play everywhere.
Recordings made in a browser often lack a duration and a seek index because the recorder never knew when it would stop. The MP4 written here has a complete index placed at the start of the file, so players show the real length and let you jump anywhere.
VP9 and AV1 compress better than H.264, so matching their quality takes more bits. filetidy aims at roughly 0.1 bit per pixel per frame, so a 1080p30 recording lands around 6 Mbit/s. If size matters more than anything, run the MP4 through the video compressor afterwards with a target in MB.
No. The H.264 MP4 produced here has no alpha channel, so the result is a normal opaque video and the see-through areas are lost. If you need transparency, keep the WebM for browsers or export a format built for it from your animation software.
It depends on your device and the video's resolution, because every frame is decoded and encoded again. Browsers with hardware H.264 encoding often go at or above real-time speed for 1080p. If your browser can't decode the WebM or lacks an encoder, filetidy uses a one-time 32 MB compatibility encoder, which works everywhere but is slower.
Yes. OBS can write WebM through its custom FFmpeg output, typically with VP8 or VP9 video and Opus or Vorbis sound, and those files are re-encoded here like any other WebM. If you plan to edit or share as MP4 anyway, recording to MKV or MP4 with H.264 in OBS spares you the slow re-encode later.
No. The WebM is decoded and re-encoded inside your browser tab, in a background worker, and the MP4 is saved straight to your device. Only the conversion program itself may be downloaded once; your recording is never uploaded.
Last updated October 28, 2026
iPhone videos are often HEVC. Copying is instant, but some Windows PCs, TVs and editors can't play HEVC.