Phones decide which way is up from their motion sensor, and they guess wrong surprisingly often: a clip started while the phone lay flat on a table, filmed from above, or recorded in a hurry can play on its side or upside down. Webcam and screen captures sometimes come out mirrored. Watching it with your head tilted is not a fix.
This tool rotates MP4, MOV, WebM, MKV and AVI files by 90 degrees either way or by 180 degrees, flips them horizontally or vertically, and saves the result in the same format. For a plain turn of an MP4 or MOV file it does not touch the picture at all, so the result is ready almost at once and identical in quality.
Two ways to rotate a video
MP4 and MOV files can carry a small piece of metadata, a rotation tag (strictly a display matrix), that tells players to turn the picture while showing it. This is in fact how phones store portrait video: the frames are recorded sideways and the tag says to show them upright. Changing only that tag rotates the video without decoding or re-encoding a single frame, so it is lossless and takes seconds even for a large file. The tool does this automatically whenever you rotate an MP4 or MOV without flipping it.
The other way is to rewrite the pixels: decode every frame, turn or mirror it, and encode it again. That is necessary for a flip, which a rotation tag cannot express, for WebM, MKV and AVI, which have no such tag here, and for players that ignore the tag. It takes longer and adds a small generation of compression, but the result looks right everywhere.
When rotating or flipping helps
Sideways phone videos
Choose 90° right or 90° left, whichever brings the top of the scene to the top. The turn is applied on top of how the clip currently plays, so you pick what you see is wrong, not what the file stores.
Upside-down clips
Action cameras mounted under a helmet or a bike, and phones held the wrong way round, produce footage that needs 180°.
Mirrored webcam and selfie footage
Some cameras and apps save a mirror image, so text reads backwards. Flip Horizontal swaps left and right; Flip Vertical turns the image over top to bottom.
The options and the re-encode switch
Rotate offers 90° right (the default), 180°, 90° left and None; Flip offers None, Horizontal and Vertical. You can combine a turn with a flip, in which case the picture is turned first and then mirrored. With a turn and no flip, MP4 and MOV files keep their video and sound streams byte for byte and only the rotation tag changes. Everything else is re-encoded in the original container: H.264 and AAC for MP4, MOV and MKV, VP8 and Vorbis for WebM, MPEG-4 Part 2 and MP3 for AVI, at a balanced quality.
Most current players, browsers, phones and social networks respect the rotation tag. Some older players, certain video editors and a few upload services ignore it and show the original sideways frames. If that happens, switch on Re-encode for players that ignore rotation: the pixels are then turned for real. The re-encoding is done by the site's ffmpeg-based converter, which downloads once (about 31 MB) and runs on your device; tag-only rotations finish in moments regardless of length.
Comment utiliser cet outil
- Drop one or more videos on the box above. MP4, MOV, WebM, MKV and AVI files up to 500 MB are accepted.
- Choose Rotate: 90° right, 180°, 90° left or None.
- Choose Flip if the picture is mirrored, and switch on Re-encode for players that ignore rotation if a previous result still played sideways somewhere.
- Press Convert and download each file, which ends in -rotated, or all of them as a ZIP.
Limitations
- Only quarter turns are possible. Straightening a slightly tilted horizon needs a video editor.
- Tag-only rotation depends on the player honouring the tag. Use the re-encode switch when you cannot control where the video will be played.
- Flipping, re-encoding and any rotation of WebM, MKV or AVI files take as long as a conversion and are slowest on phones.
- Only the main video track and the sound are kept; subtitle tracks and extra data streams are not carried over.