将背景图片设置为具有透明背景iOS

Question

我有一个应用程序，我有一个透明背景的视频，我需要设置一个背景图像到该视频并将其保存在我的画廊或其他任何，我已经尝试在我的视图上播放视频并记录整个屏幕用这样的东西：

- (void)startScreenRecording {
    self.screenRecorder = [RPScreenRecorder sharedRecorder];
    if (self.screenRecorder.isRecording) {
        return;
    }
    NSError *error = nil;
    NSArray *pathDocuments = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *outputURL = pathDocuments[0];

    NSString *videoOutPath = [[outputURL stringByAppendingPathComponent:[NSString stringWithFormat:@"%u", arc4random() % 1000]] stringByAppendingPathExtension:@"mp4"];
    if (@available(iOS 11.0, *)) {
        NSDictionary *videoSettings = @{AVVideoCompressionPropertiesKey : compressionProperties,
                                        AVVideoCodecKey                 : AVVideoCodecTypeH264,
                                        AVVideoWidthKey                 : width,
                                        AVVideoHeightKey                : height};

        self.assetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
    } else {
        // Fallback on earlier versions
    }

    [self.assetWriter addInput:self.assetWriterInput];
    [self.assetWriterInput setMediaTimeScale:60];
    [self.assetWriter setMovieTimeScale:60];
    [self.assetWriterInput setExpectsMediaDataInRealTime:YES];

    if (@available(iOS 11.0, *)) {
        [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
            dispatch_async(dispatch_get_main_queue(), ^{
                if (granted)
                {
                    [self.screenRecorder setMicrophoneEnabled:YES];

                    [self.screenRecorder startCaptureWithHandler:^(CMSampleBufferRef  _Nonnull sampleBuffer, RPSampleBufferType bufferType, NSError * _Nullable error) {
                        if (CMSampleBufferDataIsReady(sampleBuffer)) {
                            if (self.assetWriter.status == AVAssetWriterStatusUnknown && bufferType == RPSampleBufferTypeVideo) {
                                [self.assetWriter startWriting];
                                [self.assetWriter startSessionAtSourceTime:CMSampleBufferGetPresentationTimeStamp(sampleBuffer)];
                                [videoView play];
                            }

                            if (self.assetWriter.status == AVAssetWriterStatusFailed) {
                                NSLog(@"An error occured.");
                                //show alert
                                [[RPScreenRecorder sharedRecorder] stopCaptureWithHandler:^(NSError * _Nullable error) {}];
                                return;
                            }
                            if (bufferType == RPSampleBufferTypeVideo) {
                                if (self.assetWriterInput.isReadyForMoreMediaData) {
                                    [self.assetWriterInput appendSampleBuffer:sampleBuffer];
                                }else{
                                    NSLog(@"Not ready for video");
                                }
                            }
                        }
                    } completionHandler:^(NSError * _Nullable error) {
                        if (!error) {
                            AVAudioSession *session = [AVAudioSession sharedInstance];
                            [session setActive:YES error:nil];
                            // Start recording
                            NSLog(@"Recording started successfully.");
                        }else{
                            //show alert
                        }
                    }];
                }
            });
        }];


    } else {
        // Fallback on earlier versions
    }
}

但似乎质量低且速度慢，还有其他建议吗？