Containers and codecs
A video file is a container (MP4, MOV, WebM, MKV) holding streams encoded with a codec (H.264, HEVC, VP9 or AV1 for video; AAC, Opus or MP3 for sound). Converting between containers that can hold the same codecs, such as MOV to MP4 with H.264 inside, is just repackaging: the tool copies the streams, which is nearly instant and loses nothing. Converting to a container that cannot hold the codec, such as H.264 into WebM, needs re-encoding, which takes as long as compressing the video.
| From | To | What happens |
|---|---|---|
| MOV (H.264) | MP4 | Copied, seconds |
| MOV (HEVC, iPhone) | MP4 | Copied; for maximum compatibility use the compress tool to get H.264 |
| MKV (H.264) | MP4 | Copied; subtitles are not carried over |
| WebM (VP9) | MP4 | Re-encoded to H.264 |
| MP4 (H.264) | WebM | Re-encoded to VP9 |
Rotate, mute and speed
- Rotate fixes sideways phone videos. It is applied as rotation metadata where the format allows, which is instant.
- Remove the sound drops the audio stream, for background videos and clips with unwanted noise.
- Speed from 0.5× (slow motion) to 2× (fast) retimes every frame and re-encodes; the sound is removed.
Which format to choose
MP4 with H.264 plays on every phone, computer, TV and website. Choose WebM for websites that want royalty-free formats, MOV for Apple editing workflows, and MKV for archiving with several tracks. When in doubt, choose MP4.
Why it is slower than a desktop app, and when to use HandBrake
This tool uses your browser's own video encoders through WebCodecs, often the same hardware encoders a desktop app would use, but it runs inside a browser tab with a fraction of the computer's memory and without the tuned encoders desktop apps ship. Short clips are quick; a 10-minute 1080p video can take several minutes on a laptop and longer on a phone. The tool refuses files that are likely to run out of memory rather than failing halfway. For long videos, 4K footage, batches of large files, or precise control over the encoder, use HandBrake, which is free, open-source and much faster for heavy work.
Browser support and troubleshooting
The line at the top of the tool lists the video and audio codecs this browser can encode. Current Chrome and Edge on Windows and Mac handle H.264, VP9 and AV1 with AAC and Opus; Safari adds HEVC; Firefox supports WebCodecs from version 130. If a file will not open:
- "This browser cannot decode…" usually means HEVC (H.265) video, common from iPhones, in a browser without HEVC support. Try Safari or Edge on a computer with hardware HEVC, or convert it on the phone (Settings › Camera › Formats › Most Compatible for future videos).
- "Cannot read this file's format" means an old or unusual container such as AVI, WMV or FLV that browsers cannot read. Convert it with HandBrake first.
- It stops or the tab reloads on long or 4K videos: the tab ran out of memory. Trim the video into parts, close other tabs, or use a desktop app.
- Very slow on a phone or an older laptop: the browser may be using software encoding. Shorter clips and lower resolutions help.
Copying versus re-encoding
Copying streams keeps every bit of the original picture and sound and finishes in seconds whatever the length, because nothing is decoded. Re-encoding decodes every frame and compresses it again: it takes roughly as long as the video plays on a fast computer (often much less with hardware encoding), and each re-encode loses a little quality, invisible at the settings used here but cumulative if you re-encode the same file many times. The result line tells you which happened: "copied without re-encoding" or "re-encoded".
Troubleshooting playback
- An MP4 plays without picture on an older TV or Windows PC: the video inside may be HEVC. Use the compress tool, which always writes H.264.
- A rotated video still appears sideways in an editor: some editors ignore rotation metadata. Convert with a speed change of 1× and rotation, then compress it, which writes the rotation into the frames.
- MKV subtitles are missing: subtitle tracks are not carried over. Keep the original MKV if you need them.
Batch conversion
With the video licence you can choose up to 20 files at once; each is converted with the same settings, one after another, and listed with its own download button. Free use converts one file at a time with no other limits on features.
Privacy
Your video never leaves your device. It is read and written in the browser tab; there is no upload, no server-side processing and no account. You can disconnect from the internet after the page has loaded and it still works. Free use has no watermark and covers files up to 500 MB and 10 minutes; the A$9 lifetime licence removes those limits (your device's memory still applies), queues up to 20 files and saves presets.