video captured from iphone gets rotated when converted to .mp4 using ffmpeg

Question

When I try to upload videos captured from my iPhone in my app, the server performs a conversion from .mov to .mp4 so that it can be played in other platforms. However the pr

Answer 1

For sake of completeness, the reason this is happening is that iPhones only actually capture video in one fixed orientation. The measured orientation is then recorded in Apple-specific metadata.

The effect is that Quicktime Player reads the metadata and rotates the video to the correct orientation during playback, but other software (e.g., VLC) does not and shows it as oriented in the actual codec data.

This is why rotate=90 (or vflip, or transpose, or etc.) will work for some people, but not others. Depending on how the camera is held during recording, the rotation necessary could be 90, 180, or even 270 degrees. Without reading the metadata, you're just guessing at how much rotation is necessary and the change that fixes one video will fail for another.