Recording MP4 with OpenCV VideoWriter on iOS and Setting Video Bitrate

enum VideoWriterProperties {
  VIDEOWRITER_PROP_QUALITY = 1,    //!< Current quality (0..100%) of the encoded videostream. Can be adjusted dynamically in some codecs.
  VIDEOWRITER_PROP_FRAMEBYTES = 2, //!< (Read-only): Size of just encoded video frame. Note that the encoding order may be different from representation order.
  VIDEOWRITER_PROP_NSTRIPES = 3,   //!< Number of stripes for parallel encoding. -1 for auto detection.
  VIDEOWRITER_PROP_IS_COLOR = 4,   //!< If it is not zero, the encoder will expect and encode color frames, otherwise it
                                   //!< will work with grayscale frames.
  VIDEOWRITER_PROP_DEPTH = 5,      //!< Defaults to CV_8U.
  VIDEOWRITER_PROP_HW_ACCELERATION = 6, //!< (**open-only**) Hardware acceleration type (see #VideoAccelerationType). Setting supported only via `params` parameter in VideoWriter constructor / .open() method. Default value is backend-specific.
  VIDEOWRITER_PROP_HW_DEVICE       = 7, //!< (**open-only**) Hardware device index (select GPU if multiple available). Device enumeration is acceleration type specific.
  VIDEOWRITER_PROP_HW_ACCELERATION_USE_OPENCL= 8, //!< (**open-only**) If non-zero, create new OpenCL context and bind it to current thread. The OpenCL context created with Video Acceleration context attached it (if not attached yet) for optimized GPU data copy between cv::UMat and HW accelerated encoder.
  VIDEOWRITER_PROP_BITRATE = 9,
#ifndef CV_DOXYGEN
  CV__VIDEOWRITER_PROP_LATEST
#endif
};

cv::Ptr<cv::IVideoWriter> cv::create_AVFoundation_writer(const std::string& filename, int fourcc,
                                                         double fps, const cv::Size &frameSize,
                                                         const cv::VideoWriterParameters& params)
{
    CvSize sz = { frameSize.width, frameSize.height };
    const bool isColor = params.get(VIDEOWRITER_PROP_IS_COLOR, true);
    const int bitrate = params.get(VIDEOWRITER_PROP_BITRATE, 600000);
    CvVideoWriter_AVFoundation* wrt = new CvVideoWriter_AVFoundation(filename.c_str(), fourcc, fps, sz, bitrate, isColor);
    return cv::makePtr<cv::LegacyWriter>(wrt);
}

CvVideoWriter_AVFoundation::CvVideoWriter_AVFoundation(const char* filename, int fourcc,
        double fps, CvSize frame_size,
        int bitrate, int is_color) {

NSDictionary* videoCompressionSetting = [NSDictionary dictionaryWithObjectsAndKeys:
        [NSNumber numberWithInteger:bitrate], AVVideoAverageBitRateKey,
        nil]; // 设置 AVAssetWriterInput 编码码率

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
        codec, AVVideoCodecKey,
        [NSNumber numberWithInt:movieSize.width], AVVideoWidthKey,
        [NSNumber numberWithInt:movieSize.height], AVVideoHeightKey,
        videoCompressionSetting, AVVideoCompressionPropertiesKey,
        nil];

 mMovieWriterInput = [[AVAssetWriterInput
        assetWriterInputWithMediaType:AVMediaTypeVideo
        outputSettings:videoSettings] retain];

python platforms/ios/build_framework.py ios --iphoneos_archs armv7,arm64 --iphonesimulator_archs i386,x86_64

cv::VideoWriter writer;
cv::Size size = cv::Size(480, 640);
  int myFourcc = cv::VideoWriter::fourcc('H', '2', '6', '4');
  double fps = 30;
  std::vector<int> vect;
  vect.push_back(cv::VIDEOWRITER_PROP_BITRATE);
  vect.push_back(450*1000); // 更改 video 码率
  // outputPath = @"document/video.mp4" 存储路径
  writer.open([outputPath UTF8String], cv::CAP_AVFOUNDATION, myFourcc, fps, size, vect);