Current ExifTool will not accept to write the Rotation tag in a MPEG4 video file.
I tried with a video created on an Android phone and on a MP4 video file created using HandBreak with output profile "Android"
File Type : MP4
MIME Type : video/mp4
Major Brand : MP4 v2 [ISO 14496-14]
Minor Version : 0.0.0
Compatible Brands : mp42, isom, avc1
exiftool -Rotation VID_20131125_223725.mp4 VID_20131125_223750.mp4
======== VID_20131125_223725.mp4
Rotation : 90
======== VID_20131125_223750.mp4
Rotation : 0
2 image files read
exiftool -tagsFromFile VID_20131125_223725.mp4 -Rotation VID_20131125_223750.mp4
0 image files updated
1 image files unchanged
exiftool -Rotation=90 VID_20131125_223750.mp4
0 image files updated
1 image files unchanged
Correct. Changing the rotation of an MP4 video would be fairly complex. I'm not even sure I know how to do this. The Rotation tag is a Composite tag based on the MatrixStructure tag extracted from the video track. This matrix controls more than just rotation. It may also control things like aspect ratio, but I don't know for sure. Also, there are other places where matrices are stored in the file, and I don't know which of these would be need to be changed. My opinion is that this comes too close to image manipulations, and ExifTool doesn't venture into this realm. I suggest finding a video editor to do this.
- Phil