Incorrect frame rate selectiion for QCamera on iOS

Per the QCameraFormat docs, "the camera will always try to use the highest frame rate supported by a certain video format." However, the code used to select the frame rate pick the first match it finds, rather than the best match. For example, when requesting a 240 fps camera on iOS, I get a 60 fps camera, since 60 fps is with the bounds specified by the [minFrameRate, maxFrameRate] request of [2, 240].

The current code, in qtmultimedia/src/plugins/multimedia/darwin/camera.avfcamerautility.mm line 125:]

 

{{ if (frameRateRange.minFrameRate >= cameraFormatPrivate->minFrameRate
&& frameRateRange.maxFrameRate <= cameraFormatPrivate->maxFrameRate) {}}

      {{ newFormat = format;}}

       {{ break;}}

{} }{}{}

Note that this picks the first match, not the best match. My revised code:

{{   AVCaptureDeviceFormat *newFormat = nil;
    qreal newFormatMaxFrameRate = 0;
    NSArray<AVCaptureDeviceFormat *> *formats = captureDevice.formats;
    for (AVCaptureDeviceFormat *format in formats) {
        CMFormatDescriptionRef formatDesc = format.formatDescription;
        CMVideoDimensions dim = CMVideoFormatDescriptionGetDimensions(formatDesc);
        FourCharCode cvPixFormat = CMVideoFormatDescriptionGetCodecType(formatDesc);

        if (requiredCvPixFormat == cvPixFormat
            && cameraFormatPrivate->resolution == QSize(dim.width, dim.height)
            && (!cvFormatValidator || cvFormatValidator(cvPixFormat))) {
            for (AVFrameRateRange *frameRateRange in format.videoSupportedFrameRateRanges) {
                if (frameRateRange.minFrameRate >= cameraFormatPrivate->minFrameRate
                    && frameRateRange.maxFrameRate <= cameraFormatPrivate->maxFrameRate
                    && (newFormat == nil || newFormatMaxFrameRate < frameRateRange.maxFrameRate))

{                     newFormat = format;                     newFormatMaxFrameRate = frameRateRange.maxFrameRate;                 }

            }
        }}}

 

Note that this source file does contain a qt_find_best_framerate_match function that might be helpful.