ios - AVAssetWriterを使用して縮小サイズのビデオを作成するにはどうすればよいですか？

Question

縮小サイズのビデオを作成します。おそらく、幅が50ピクセル、長さが75ピクセルです。それらは物理的な次元です。

どのように設定しますか？ビデオ設定で？AVVideoWidthKeyとAVVideoHeightKeyは、私が必要としていた物理的な寸法ではなく、解像度のためのものだと思います。

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               [NSNumber numberWithInt: 320], AVVideoWidthKey,    
                               [NSNumber numberWithInt:480], AVVideoHeightKey,   
                               nil];
AVAssetWriterInput* writerInput = [[AVAssetWriterInput
                                    assetWriterInputWithMediaType:AVMediaTypeVideo
                                    outputSettings:videoSettings] retain

Answer 1

ビデオ コーデック パラメータを設定する必要があります。

NSDictionary *videoCleanApertureSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                           [NSNumber numberWithInt:320], AVVideoCleanApertureWidthKey,
                                           [NSNumber numberWithInt:480], AVVideoCleanApertureHeightKey,
                                           [NSNumber numberWithInt:10], AVVideoCleanApertureHorizontalOffsetKey,
                                           [NSNumber numberWithInt:10], AVVideoCleanApertureVerticalOffsetKey,
                                            nil];


NSDictionary *videoAspectRatioSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                                             [NSNumber numberWithInt:3], AVVideoPixelAspectRatioHorizontalSpacingKey,
                                             [NSNumber numberWithInt:3],AVVideoPixelAspectRatioVerticalSpacingKey,
                                                    nil];



NSDictionary *codecSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               [NSNumber numberWithInt:960000], AVVideoAverageBitRateKey,
                               [NSNumber numberWithInt:1],AVVideoMaxKeyFrameIntervalKey,
                               videoCleanApertureSettings, AVVideoCleanApertureKey,
                               //videoAspectRatioSettings, AVVideoPixelAspectRatioKey,
                               //AVVideoProfileLevelH264Main30, AVVideoProfileLevelKey,
                               nil];





NSString *targetDevice = [[UIDevice currentDevice] model];

NSDictionary *videoSettings = [NSDictionary dictionaryWithObjectsAndKeys:
                               AVVideoCodecH264, AVVideoCodecKey,
                               codecSettings,AVVideoCompressionPropertiesKey,
                               [NSNumber numberWithInt:320], AVVideoWidthKey,
                               [NSNumber numberWithInt:480], AVVideoHeightKey,
                               nil];

Answer 2

AVAssetWriter を使用するには PhD が必要です 。 TP40010188-CH9-SW1

ビットレートの変更などのより重要な機能を備えた AVAssetExportSession ドロップイン置換である、まさにあなたが望むことを行うための素晴らしいライブラリがあります: https://github.com/rs/SDAVAssetExportSession

使用方法は次のとおりです。

-(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,
    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);
    }
  }];
}