Rotate video online

Why videos end up sideways

Phones decide orientation from the motion sensor at the moment you press record. Several everyday situations confuse it:

• Starting a recording with the phone lying flat on a table or pointing straight down, where the sensor cannot tell which edge is up.
• Rotation lock switched on while you turn the phone to landscape.
• Turning the phone halfway through a clip. Orientation is fixed at the start and does not follow the turn.
• Action cameras, dashcams and drones mounted upside down.

Most phones do not actually rotate the pixels. They store the image as the sensor saw it and add a small rotation flag to the file that tells players how to show it. Players that respect the flag show the clip correctly; some editors, older TVs, web players and upload pipelines ignore it, so the same file looks fine on the phone and sideways everywhere else.

How the rotation is applied

This tool rotates the actual pixels and produces a new MP4 that needs no flag at all.

1. FFmpeg reads the video and applies any rotation flag already in the file, so the starting point is the clip as it appears in a normal player.
2. The chosen rotation is applied on top: 90° turns the picture clockwise, 270° turns it counter-clockwise, 180° turns it upside down.
3. The video is encoded again as H.264 at CRF 23 with standard 8-bit 4:2:0 colour and written as an MP4 with its index at the start.
4. AAC audio is copied unchanged; any other audio is converted to AAC at 128 kbit/s.

Because step 1 uses what you actually see, choose the angle by looking at the clip in your usual player:

• People's heads point to the left: choose 90°.
• People's heads point to the right: choose 270°.
• The picture is upside down: choose 180°.

A 90° or 270° rotation swaps width and height, so a 1920×1080 landscape file becomes 1080×1920 portrait. A 180° rotation keeps the dimensions. The tool only rotates; it does not mirror the picture, so a selfie video that reads backwards stays that way.

Quality, size and speed

Rotation cannot be done without re-encoding, because every frame has to be rebuilt in a new orientation. CRF 23 is a constant-quality setting at which the difference from the original is hard to see in normal viewing, and resolution and frame rate are unchanged.

In the browser FFmpeg runs as WebAssembly with the fast encoder preset. Expect roughly real-time speed on a recent laptop for 1080p, slower for 4K and on phones. The server option uses native FFmpeg with the slower medium preset and the same CRF, which usually gives a somewhat smaller file and finishes much faster on long clips.

Output size often differs from the input. Footage recorded in HEVC on a recent iPhone can grow, because H.264 needs more bits for the same quality. Footage from older devices or heavily compressed downloads may shrink a little. If the result is too large to send, compress video can reduce it further.

Formats and limits

• Input: MP4, MOV and WebM files up to 2 GB in the browser. Output is always an MP4 named after the original with -rotated added.
• AAC audio is copied, the rest converted. Phone and camera MP4 and MOV files with AAC sound keep it untouched. Opus or Vorbis from WebM files and uncompressed PCM from some cameras and audio recorders are converted to AAC, so the MP4 plays in any player and editor.
• Memory. In the browser the input and output are held in memory together, so multi-gigabyte files on a phone may fail.
• Server processing. One free server job a day for files up to 500 MB; Premium is unlimited and accepts up to 4 GB. Files are deleted automatically within about an hour.

Tips

• One angle applies to every file in a batch. If clips need different corrections, run them in separate groups.
• Use trim video before rotating when you only need part of a clip. Both steps re-encode, but rotating a 30-second excerpt is far quicker than rotating a 20-minute recording.
• Only part of a clip sideways because the phone was turned mid-recording? Cut that section out first, rotate just that piece, and keep the rest as it was.
• Keep the original. Each re-encode loses a small amount of detail, and the original with its rotation flag is still the best source if you need to try again.