It's been a long time, but I once wrote code to parse and rewrite ['rotate'] the matrices at a previous job. The "Matrix Structure" is in the 'mvhd' atom. See

It's been a long time, but I once wrote code to parse and rewrite ['rotate'] the matrices at a previous job. The "Matrix Structure" is in the 'mvhd' atom. See: * https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap2/qtff2.html#//apple_ref/doc/uid/TP40000939-CH204-32947 https://developer.apple.com/library/archive/documentation/Qu... * https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap4/qtff4.html#//apple_ref/doc/uid/TP40000939-CH206-18737 https://developer.apple.com/library/archive/documentation/Qu... [Some of the best documentation for MP4 that I've seen on the web is from Apple, since it grew out of QuickTime.]