iOS AVFoundation Video Capture Orientation Options

Question

I have an app that I would like to have video capture for the front-facing camera only. That's no problem. But I would like the video capture to always be in landscape, even when the phone is being held in portrait.

I have a working implementation based on the AVCamDemo code that Apple published. And borrowing from the information in this tech note, I am able to specify the orientation. There's just one trick: while the video frame is oriented correctly, the contents still appear as though shot in portrait:

I'm wondering if I'm just getting boned by the physical constraints of the hardware: is the image sensor just oriented this way? The referenced tech note above makes this note:

Important: Setting the orientation on a still image output and movie file output doesn't physically rotate the buffers. For the movie file output, it applies a track transform (matrix) to the video track so that the movie is rotated on playback, and for the still image output it inserts exif metadata that image viewers use to rotate the image properly when viewing later.

But my playback of that video suggests otherwise. Any insight or suggestions would be appreciated!

Thanks, Aaron.

Answer 1

To answer your question, yes, the image sensor is just oriented that way. The video camera is an approx 1-megapixel "1080p" camera that has a fixed orientation. The 5MP (or 8MP for 4S, etc) still camera also has a fixed orientation. The lenses themselves don't rotate nor do any of the other camera bits, and hence the feed itself has a fixed orientation.

"But wait!", you say, "pictures I take with the camera app (or API) get rotated correctly. Why is that?" That's cuz iOS takes a look at the orientation of the phone when a picture is taken and stores that information with the picture (as an Exif attachment). Yet video isn't so flagged -- and each frame would have to be individually flagged, and then there's issues about what to do when the user rotates the phone during video....

So, no, you can't ask a video stream or a still image what orientation the phone was in when the video was captured. You can, however, directly ask the phone what orientation it is in now:

UIDeviceOrientation currentOrientation = [UIDevice currentDevice].orientation;

If you do that at the start of video capture (or when you grab a still image from a video feed) you can then use that information to do your own rotation of playback.