How the rotation is applied
Pick a direction and export. The picture is genuinely rotated frame by frame and the video is re-encoded to MP4 with H.264 video and AAC audio. That is the important detail, and it is worth understanding before you choose a tool for this job.
Many rotation tools do not touch the picture at all. They flip a rotation flag in the file metadata, which players are supposed to read and respect. It is instant and lossless, and it works right up until the file reaches something that ignores the flag, which is when you get a sideways video in an editor, on a smart TV, or in an upload form. This tool takes the slower route and rewrites the actual pixels, so there is no flag left for anything to ignore.
The trade is that re-encoding takes time and costs a small amount of quality, the way any re-encode does. The encoder runs at a high quality setting, so the loss is not something you will see on ordinary footage, but it is not a free operation and it is not instant.
- Load a video and pick 90 left, 90 right, or 180
- The picture is rotated and re-encoded to MP4
- Audio is carried through
Which direction do you need
The quickest way to decide is to look at where the top of your subject currently points. If the top of the image points to the left of the screen, you need to rotate 90 degrees right. If it points to the right, rotate 90 degrees left. If everything is upside down, use 180.
The 180 case is more common than people expect. It happens when a phone was held upside down, when a clip came from a camera mounted inverted on a rig, or when a screen recording was made on a rotated display.
A rotation of 90 degrees in either direction also swaps the dimensions of the video. A 1920 by 1080 landscape clip becomes 1080 by 1920 portrait. That is what you want when the footage was shot in the wrong orientation, and it is worth knowing before you rotate a clip that was already the right shape.
File size and what else you might need
The whole video is held in browser memory while it is processed, so there is a real ceiling. Files above roughly 1.5 GB are rejected with a message rather than being allowed to fail partway through an export, because the memory the encoder can use runs out before the run finishes.
If your file is above that, trim it into sections with Video Trimmer, rotate each one, and join them with Merge Videos. That is more work than one pass, but it completes.
Rotation is a distinct job from cropping, and they are often confused. Rotating turns the whole frame. If instead you want to change the shape of the frame, cut a landscape clip into a portrait one for example, that is Video Cropper, which lets you drag a selection at a fixed aspect ratio.
- Files above roughly 1.5 GB are rejected up front
- Split, rotate, and rejoin for anything larger
- Use Video Cropper if you want to change the frame shape rather than turn it