The video looked fine on your phone. Then you opened it on a laptop, sent it to someone, played it on the TV or uploaded it to a course site, and it came out lying on its side or upside down. It feels like the file got damaged on the way. Almost always it didn't: the picture is exactly as it was, and one small piece of information about how to turn it got lost or ignored. Once you know which, the fix takes a second and costs nothing in quality.
The quick answer
| What you see | Most likely cause | What to do |
|---|---|---|
| Upright on the phone, sideways in one app, TV or website | That app ignores the rotation note in the file | Rotate with “Turn the pixels” so the turn is in the picture itself |
| Sideways everywhere, including on the phone | The phone wrote the wrong note, usually because it was lying flat when you pressed record | Turn it a quarter in Rotate video; no re-encoding needed |
| Upside down everywhere | Same as above, 180° | 180° in Rotate video |
| Correct way up, but text reads backwards | A front-camera (selfie) video, mirrored | Flip left–right in Rotate video |
| Upright, but a tall video has black bars or a wide one is cut off | The app wants a different shape | Crop video to 9:16, 4:5 or square |
Why it happens: phones store vertical video on its side
A phone camera's sensor is wider than it is tall, and it always records that way. When you hold the phone upright, it doesn't turn the picture before saving. It saves the frames sideways and adds a short note to the file: “turn this 90° clockwise when you play it”. In an MP4 or MOV that note is a little grid of numbers next to the video, and the phone writes it from its motion sensor at the moment you start recording.
We checked this on a 1080p clip stored the way phones store vertical video. A program that reads the frames without the note, like the video library our test suite uses, sees a 1920×1080 picture lying on its side. Chrome, which reads the note, shows the same file as an upright 1080×1920 video. Same bytes, two different pictures, depending only on whether the note is read.
That explains both kinds of sideways video:
- Fine on the phone, sideways somewhere else: the somewhere else is ignoring the note. Users on the Plex forums, for example, have reported iPhone videos that play correctly on a computer and sideways through a particular TV app. The file is fine.
- Sideways everywhere: the note itself is wrong. When the phone is flat on a table or pointed at the floor, its motion sensor can't tell which way is up, and it guesses. The guess is written into the file and every player obeys it.
What we found when we tested rotation
We made a short test video with four coloured quarters (red top left, green top right, blue bottom left, white bottom right), so that any turn or mirror shows up at a glance. Then we changed only the note, without touching the frames, and looked at the result in two places on Windows 11:
| Note in the file | Chrome | File Explorer thumbnail | Frames changed |
|---|---|---|---|
| Turn 90° right | correct | correct | 0 of 60 |
| Turn 180° | correct | correct | 0 of 60 |
| Turn 90° left | correct | correct | 0 of 60 |
| Mirror left–right | correct | ignored — not mirrored | 0 of 60 |
Two lessons. First, a rotation note is a reliable way to turn a video in mainstream software, and it costs nothing: the frames are not decoded, so there is no quality loss and the file stays the same size. Second, a mirror note is not reliable: the same Windows that honoured every turn showed the mirrored file unmirrored. If you need a video mirrored, the mirror has to be built into the picture.
How to fix a sideways video without losing quality
- Open Rotate video and drop the file in. It works in the browser on Windows, Mac, Chromebook or a phone, and the video isn't uploaded.
- Press 90° left, 90° right or 180° until the preview is the right way up.
- Keep Keep quality selected and press Rotate video. Only the note changes; the page then compares every frame with the original and shows the count (all 360 of 360 on a 12-second phone clip, in 0.06 seconds).
- Download it and check it where it went wrong before.
If it is still sideways in that one app or TV, that app ignores notes altogether. Run it again with Turn the pixels. That decodes the video, turns every frame and encodes it again at about the original bitrate, so the picture is upright with no note at all and every player has to show it the same way. It takes longer and is a re-encode, so use it only when you need it.
On the phone itself
Both iPhone and Android can rotate a video in the built-in gallery: on an iPhone, open the video in Photos, tap Edit, then the crop tool and the rotate button; on most Android phones, Edit and then Rotate in Google Photos or the maker's gallery. We haven't measured whether those re-encode the video. They are the quickest route if the video is still on the phone and you only need to fix it once.
Mirrored selfie videos
Front cameras show you a mirror image while you record, because that feels natural, and some phones save it that way too. Writing on a T-shirt or a sign then reads backwards. Use Flip left–right in Rotate video. For the reason in the test above, that always rebuilds the picture rather than adding a mirror note.
Common questions
Why does my video turn sideways after I upload it? Some sites and course platforms re-process uploads, and software that drops the note on the way. Turning the pixels before you upload avoids it, because there is no note left to drop.
Will rotating make the file smaller or bigger? A note-only rotation keeps the size exactly. Turning the pixels re-encodes, which can come out slightly smaller or larger. If the file is too big to send, Compress video brings it under a set size.
The video is upright now but doesn't fill the screen on Reels or TikTok. That's the shape, not the rotation. Crop video cuts it to 9:16, 4:5 or square, and shows the exact pixel size before you start.