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Different number of mappedBytes in QVideoFrame in android versus ios

  • I'm working on a mobile application where I would like to process a QVideoFrame in OpenCV (or QImage). I am able to properly receive a QVideoFrame in Android, where I receive a logical number of bytes (3110400 for a 1920x1080 image). When I run the same code on ios, i receive a weird number of bytes (3136384 for a 1920x1080 image).

    After I map the QVideoFrame, I am able to properly process the Image using the NV21 format (as reported by the QVideoFrame pixelFormat() function). In ios, I am able to process the image (using the NV12 format), but I noticed that there is a shift in the colors (about 16 columns to the left). This is unsurprising, as I am only reading in 3110400 bytes versus the full 3136384 bytes.

    Both Android and ios report a QVideoFrame size of 1920x1080. Is there a way to properly read a QVideoFrame for processing such that there is no shift in the data?

  • I was able to resolve the issue by changing the QCameraViewFinderSettings on my QCamera to use QVideoFrame::Format_ARGB32 @ 1920x1080. After this change, the QVideoFrame reported the proper number of mappedBytes.

    One interesting note, I had to QCameraViewFinderSettings.setMinimumFrameRate(0). For some reason there was a lag on the viewfinder in low light, but changing this setting fixed it.