Question

我正在开展个人iOS项目，需要通过4G连接上传到后端的全屏视频（长度为15秒）。虽然我可以很好地拍摄视频，但文件的输出大小达到了30MB，这让我觉得在压缩方面我做错了严重错误。以下是我用来设置AssetWriter的代码：

-(void)captureOutput:(AVCaptureFileOutput *)captureOutput didStartRecordingToOutputFileAtURL:(NSURL *)fileURL fromConnections:(NSArray *)connections
{
    NSLog(@"Started Recording! *******************");
    self.movieWriter = [AVAssetWriter assetWriterWithURL:fileURL fileType:AVFileTypeMPEG4 error:nil];
    [self.movieWriter setShouldOptimizeForNetworkUse:YES];

    NSDictionary *videoCleanApertureSettings = @{
                                                 AVVideoCleanApertureWidthKey: [NSNumber numberWithFloat:self.view.frame.size.width],
                                                 AVVideoCleanApertureHeightKey: [NSNumber numberWithFloat:self.view.frame.size.height],
                                                 AVVideoCleanApertureHorizontalOffsetKey: [NSNumber numberWithInt:10],
                                                 AVVideoCleanApertureVerticalOffsetKey: [NSNumber numberWithInt:10],
                                                 };

    NSDictionary *videoCompressionSettings = @{
                                          AVVideoAverageBitRateKey: [NSNumber numberWithFloat:5000000.0],
                                          AVVideoMaxKeyFrameIntervalKey: [NSNumber numberWithInteger:1],
                                          AVVideoProfileLevelKey: AVVideoProfileLevelH264Baseline30,
                                          AVVideoCleanApertureKey: videoCleanApertureSettings,
                                          };

    NSDictionary *videoSettings = @{AVVideoCodecKey: AVVideoCodecH264,
                                    AVVideoWidthKey: [NSNumber numberWithFloat:self.view.frame.size.width],
                                    AVVideoHeightKey: [NSNumber numberWithFloat:self.view.frame.size.height],
                                    AVVideoCompressionPropertiesKey: videoCompressionSettings,
                                    };

    self.movieWriterVideoInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:videoSettings];
    self.movieWriterVideoInput.expectsMediaDataInRealTime = YES;
    [self.movieWriter addInput:self.movieWriterVideoInput];

    NSDictionary *audioSettings = @{AVFormatIDKey: [NSNumber numberWithInteger:kAudioFormatMPEG4AAC],
                                    AVSampleRateKey: [NSNumber numberWithFloat:44100.0],
                                    AVNumberOfChannelsKey: [NSNumber numberWithInteger:1],
                                    };

    self.movieWriterAudioInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeAudio outputSettings:audioSettings];
    self.movieWriterAudioInput.expectsMediaDataInRealTime = YES;
    [self.movieWriter addInput:self.movieWriterAudioInput];


    [self.movieWriter startWriting];
}

-(void)captureOutput:(AVCaptureFileOutput *)captureOutput didFinishRecordingToOutputFileAtURL:(NSURL *)outputFileURL fromConnections:(NSArray *)connections error:(NSError *)error
{
    NSLog(@"Done Recording!");
    [self.movieWriterVideoInput markAsFinished];
    [self.movieWriterAudioInput markAsFinished];
    [self.movieWriter finishWritingWithCompletionHandler:^{
        AVURLAsset *compressedVideoAsset = [[AVURLAsset alloc] initWithURL:self.movieWriter.outputURL options:nil];
        //Upload video to server

    }];
}

使用以下代码设置实际会话：

            //Indicate that some changes will be made to the session
            [self.captureSession beginConfiguration];
            self.captureSession.sessionPreset = AVCaptureSessionPresetHigh;

            AVCaptureInput* currentCameraInput = [self.captureSession.inputs objectAtIndex:0];
            for (AVCaptureInput *captureInput in self.captureSession.inputs) {
                [self.captureSession removeInput:captureInput];
            }


            //Get currently selected camera and use for input
            AVCaptureDevice *videoCamera = nil;
            if(((AVCaptureDeviceInput*)currentCameraInput).device.position == AVCaptureDevicePositionBack)
            {
                videoCamera = [self cameraWithPosition:AVCaptureDevicePositionBack];
            }
            else
            {
                videoCamera = [self cameraWithPosition:AVCaptureDevicePositionFront];
            }

            //Add input to session
            AVCaptureDeviceInput *newVideoInput = [[AVCaptureDeviceInput alloc] initWithDevice:videoCamera error:nil];
            [self.captureSession addInput:newVideoInput];

            //Add mic input to the session
            AVCaptureDevice *audioDevice = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeAudio];
            AVCaptureInput *audioInput = [AVCaptureDeviceInput deviceInputWithDevice:audioDevice error:nil];
            [self.captureSession addInput:audioInput];

            //Add movie output to session
            for (AVCaptureOutput *output in self.captureSession.outputs) {
                [self.captureSession removeOutput:output];
            }

            self.movieOutput = [AVCaptureMovieFileOutput new];
            int32_t preferredTimeScale = 30; //Frames per second
            self.movieOutput.maxRecordedDuration = CMTimeMakeWithSeconds(15, preferredTimeScale); //Setting the max video length
            [self.captureSession addOutput:self.movieOutput];

            //Commit all the configuration changes at once
            [self.captureSession commitConfiguration];

我知道如果我将 AVCaptureSessionPresetHigh 更改为其他预设，我可以减少最终视频的文件大小，但不幸的是看起来像 AVCaptureSessionPresetiFrame1280x720 是唯一一个提供了我试图捕获的全帧（这使我的输出大小约为20MB，对于4G上传而言仍然太大）。

我花了很多时间在谷歌搜索上搜索Stack Overflow上的其他帖子，但我似乎无法弄清楚我在生活中做错了什么以及任何帮助我将非常感激。

Answer 1

您需要博士才能使用AVAssetWriter - 这非常重要：https://developer.apple.com/library/mac/documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/05_Export.html#//apple_ref/doc/uid/TP40010188-CH9-SW1

有一个令人惊叹的库，可以完全按照您的需要进行操作，这只是一个AVAssetExportSession直接替换，具有更重要的功能，如更改比特率：https://github.com/rs/SDAVAssetExportSession

以下是如何使用它：

-(void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{

  SDAVAssetExportSession *encoder = [SDAVAssetExportSession.alloc initWithAsset:[AVAsset assetWithURL:[info objectForKey:UIImagePickerControllerMediaURL]]];
  NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
  NSString *documentsDirectory = [paths objectAtIndex:0];
  self.myPathDocs =  [documentsDirectory stringByAppendingPathComponent:
                      [NSString stringWithFormat:@"lowerBitRate-%d.mov",arc4random() % 1000]];
  NSURL *url = [NSURL fileURLWithPath:self.myPathDocs];
  encoder.outputURL=url;
  encoder.outputFileType = AVFileTypeMPEG4;
  encoder.shouldOptimizeForNetworkUse = YES;

  encoder.videoSettings = @
  {
  AVVideoCodecKey: AVVideoCodecH264,
  AVVideoCompressionPropertiesKey: @
    {
    AVVideoAverageBitRateKey: @2300000, // Lower bit rate here
    AVVideoProfileLevelKey: AVVideoProfileLevelH264High40,
    },
  };
  encoder.audioSettings = @
  {
  AVFormatIDKey: @(kAudioFormatMPEG4AAC),
  AVNumberOfChannelsKey: @2,
  AVSampleRateKey: @44100,
  AVEncoderBitRateKey: @128000,
  };

  [encoder exportAsynchronouslyWithCompletionHandler:^
  {
    int status = encoder.status;

    if (status == AVAssetExportSessionStatusCompleted)
    {
      AVAssetTrack *videoTrack = nil;
      AVURLAsset *asset = [AVAsset assetWithURL:encoder.outputURL];
      NSArray *videoTracks = [asset tracksWithMediaType:AVMediaTypeVideo];
      videoTrack = [videoTracks objectAtIndex:0];
      float frameRate = [videoTrack nominalFrameRate];
      float bps = [videoTrack estimatedDataRate];
      NSLog(@"Frame rate == %f",frameRate);
      NSLog(@"bps rate == %f",bps/(1024.0 * 1024.0));
      NSLog(@"Video export succeeded");
      // encoder.outputURL <- this is what you want!!
    }
    else if (status == AVAssetExportSessionStatusCancelled)
    {
      NSLog(@"Video export cancelled");
    }
    else
    {
      NSLog(@"Video export failed with error: %@ (%d)", encoder.error.localizedDescription, encoder.error.code);
    }
  }];
}

AVAssetWriter输出大文件（即使应用压缩设置）

1 个答案: