Rotation metadata
Also known as: display matrix, rotate tag, sideways video
A flag stored in a video file that tells players to rotate the picture on playback; when software ignores it, clips appear sideways or upside down.
Updated
What it means
Phones and many cameras do not physically rotate the image they record. The sensor writes frames in its native landscape shape, and when you hold the device upright the file simply carries a note saying to turn the picture 90 degrees on playback. In MP4 and MOV files that note lives in the track header as a display matrix; many tools show it as a rotate value.
Most modern players read it, so you never notice. Problems appear when one step in the chain does not: an old editor, a converter, a web player or a script. Then a vertical clip plays lying on its side, or a correctly flagged clip from an inverted camera plays upside down.
How it works in practice
To see what a file says, inspect its metadata with MediaInfo or the ffprobe tool that ships with FFmpeg, which report the rotation in degrees. If the flag is wrong, you can change it without re-encoding by Remuxing with a new value, which is quick and lossless.
The alternative is to bake it in: transcode the clip with the rotation applied to the pixels and the flag cleared. The file then plays upright everywhere, in exchange for one more generation of compression. Many phone apps do this silently when they export or share.
What to watch out for
Fixing the picture twice is a common accident. If an editor reads the flag and you also rotate the clip by hand, it ends up sideways again. Check one clip in a plain player before batch-processing a whole card.
A Large file transfer service passes files through untouched, flag included, but chat apps that re-encode may apply it, drop it or get it wrong. Cameras mounted upside down add another twist: some write a flag, others flip the pixels in camera, and mixing both in one vertical project gets confusing.
How RawClip handles it
RawClip takes orientation from the footage: when every clip used is vertical the highlight is vertical, otherwise it is horizontal with vertical clips pillarboxed and nothing cropped. If a clip plays sideways in your usual desktop player, fix its rotation before uploading, so it is treated the way you meant it to look.