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Private Video Converter

Web Video Converter

Make two web-ready copies of a video in one run: H.264 in MP4, which plays everywhere, and VP9 in WebM, which is usually smaller. Both are made on your device.

H.264 MP4VP9 WebMOptional poster image

Video

Choose a video

or drop it here

The video is processed on this device and never uploaded.

MP4, MOV, WebM, MKV, AVI, WMV, FLV, 3GP, TS / MTS / M2TS or VOB / MPG

Files over 1 GB can be slow. Very large outputs need a browser that can save straight to a file.

Settings

Quality Level
Audio

The H.264 file gets AAC audio and the VP9 file gets Opus audio, both at 128 kbps.

Poster Image

A still frame to show before the video plays (the poster attribute of a video tag). Made after both videos, at the same width.

How the files are set up for the web

  • The MP4 index is at the start of the file, so playback can begin before the download finishes.
  • The H.264 file has a keyframe every 90 frames (about 3 seconds at 30 fps), so seeking is quick.
  • Both files use 4:2:0 colour, which every browser and phone can decode.

How it works

Choose a video and a quality level, then convert. The page makes the H.264 MP4 first and the VP9 WebM second, one after the other, so the two encodes never compete for memory. Each result shows its size, so you can see how much the WebM saves before you download either.

The MP4 uses H.264 video and AAC audio, which every browser and phone plays. The WebM uses VP9 video and Opus audio, which modern browsers play and which is usually smaller at the same quality. Use both in an HTML <video> element, with the WebM listed first, and each browser picks the one it supports.

An optional poster image (JPEG and WebP) can be saved from a chosen moment of the video, for the element's poster attribute. Everything is done in your browser and the video is never uploaded.

Supported files

Inputs
MP4, M4V, MOV, WebM, MKV, AVI, WMV, FLV, 3GP, MPEG-TS and MPEG-PS files, at their original size or scaled to 1080p or 720p.
Outputs
An H.264 and AAC MP4 plus a VP9 and Opus WebM, at low, medium, high or best quality, with or without audio, and an optional JPEG and WebP poster.

Limitations

  • VP9 is encoded only with the browser's WebCodecs encoder. In a browser without one the MP4 is still made and the WebM step says why it cannot run.
  • The two encodes run one after the other, so a run takes about as long as two separate conversions.
  • Very large outputs are kept in memory until downloaded; for long, high-resolution videos use a lower quality or a smaller size.

Questions

Do I need both MP4 and WebM?

Not always. An H.264 MP4 alone plays in every current browser. Adding a VP9 WebM saves bandwidth for the browsers that pick it, which matters most for large or autoplaying videos.

Which quality should I choose?

Medium suits most web pages. Low is for background or decorative videos where size matters more than detail, high for product or demo videos where people look closely, and best when quality matters more than size or encoding time.

Is the video uploaded?

No. Both files are made on your device and never leave it.