A dumb reason computer vision apps aren’t working: Exif Orientation

Re:A dumb reason computer vision apps aren’t working: Exif O... by asveikau on Wednesday October 09, 2019 @09:28PM (#21210046)

> That videos sometimes use "Rotation", not "Orientation" (and Rotation is encoded in degrees, not the crazy EXIF rotation enum)

Not technically degrees. MP4 encodes it as a matrix. (Now, there are matrices corresponding to degree transformations...)

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Re:A dumb reason computer vision apps aren’t working: Exif O... by mceachen on Wednesday October 09, 2019 @10:20PM (#21210265)

I haven't seen that: can you give me an example?

(The output of `exiftool -Rotation example.mp4` would be great!)

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Re:A dumb reason computer vision apps aren’t working: Exif O... by asveikau on Wednesday October 09, 2019 @10:42PM (#21210343)

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:

[Some of the best documentation for MP4 that I've seen on the web is from Apple, since it grew out of QuickTime.]

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