Runs on your device · Your file never leaves your device.
A clip filmed with the phone held the wrong way, a screen recording that came out on its side, a mirror-image selfie video: pick the turn, check the preview, download the fixed file. Choices are 90° clockwise, 90° counter-clockwise, 180°, flip horizontally (mirror) and flip vertically.
This tool rotates the picture itself and re-encodes it to H.264, rather than writing a rotation flag into the metadata. A flag is cheap but many players, websites and editing programs ignore it and show the video sideways anyway; rotated pixels need no flag. The audio is copied untouched whenever MP4 can carry it.
The preview shows a still frame turned the same way the video will be, so you can see that "clockwise" is the right choice before waiting for the encode. Everything runs on your device; files over 1 GB are processed in parts that fit in memory.
Not for: Straightening a slightly tilted horizon by a few degrees — this turns in steps of 90° only.
Phones often store a video the way the camera sensor sees it, lying on its side, and add a small note to the file that tells players to turn it upright. This tool applies that note first, so your choice is added on top of the picture as it is meant to be shown. The finished MP4 has the whole turn in its pixels and carries no rotation note.
Choose the turn from the preview here. If the clip already stands upright in the preview but lies on its side in another app, that app is ignoring the note and you need no turn at all: converting the file to MP4 with the Convert mode of this same tool (also at /mov-to-mp4) writes the stored rotation into the pixels in the same way.
The job goes first to the H.264 encoder built into your device, through the browser's WebCodecs interface, and the progress line says so. The built-in engine takes over when the browser has no such encoder, cannot decode the source, does not know its container (VOB, AVI, WMV, FLV, RealMedia), or when the expected result would be too big to assemble in memory: above 1.5 GB, or 400 MB on a device that reports 4 GB of memory or less. If the device encoder stops part-way, a note says so and the engine does the job instead.
The engine encodes with x264 at quality setting 23, and for clips of a minute or longer it can share the picture between up to four copies of itself. The device encoder can be much faster: on a 4-core computer with no graphics chip (so Chrome's software encoder), a 3-minute 1080p film compressed to 25 MB took 91 seconds on it and 653 seconds on the engine. That was a compression, not a rotation, but the same two encoders do this work.
On the device encoder the picture gets a bitrate worked out from its frame size and frame rate, about 3 Mbit/s for 1080p at 30 frames per second, but never more than the original picture had. On both paths the index is written at the start of the file, so it can start playing before it has fully loaded.
AAC and MP3 sound is copied untouched; the engine also copies AC-3, E-AC-3 and ALAC, and turns anything else into AAC at 128 kbit/s. Where sound has to be converted but the browser has no AAC encoder (Chrome on Linux is one), the picture is still made on the device and the engine adds the sound in a short second step.
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