如何使用AVAssetWriter保持视频的宽高比

Question

我有以下代码，它可以从相机中捕获视频并使用AVAssetWriter将其存储为QuickMovie文件。它可以正常工作，但是由于outputSettings for AVAssetWriterInput中的宽度和高度被硬编码（480 x 320），因此纵横比不完美。

我更愿意找出源视频的纵横比，并指定适当的高度（480 x 纵横比）。有人知道如何做吗？我是否应该推迟AssetWriterInput的创建直到第一个sampleBuffer？

      // 将sessionPreset设置为'medium'
      self.captureSession = [[AVCaptureSession alloc] init];
      self.captureSession.sessionPreset = AVCaptureSessionPresetMedium;
      ...
// 创建AVCaptureVideoDataOutput
      self.captureVideo = [[AVCaptureVideoDataOutput alloc] init];
      NSString* formatTypeKey = (NSString*)kCVPixelBufferPixelFormatTypeKey;
      self.captureVideo.videoSettings = @{
        formatTypeKey:[NSNumber numberWithInt:kCVPixelFormatType_32BGRA]
      };
      [self.captureVideo setSampleBufferDelegate:self queue:dispatch_get_main_queue()];
// 创建AVAssetWriter
      NSError* error = nil;
      self.videoWriter = [[AVAssetWriter alloc] initWithURL:url 
                             fileType:AVFileTypeQuickTimeMovie
                             error:&error];
      ...
      // 使用指定的设置创建AVAssetWriterInput
      NSDictionary* compression = @{
        AVVideoAverageBitRateKey:[NSNumber numberWithInt:960000],
        AVVideoMaxKeyFrameIntervalKey:[NSNumber numberWithInt:1]
      };
      self.videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
            outputSettings:@{
              AVVideoCodecKey:AVVideoCodecH264,
              AVVideoCompressionPropertiesKey:compression,
              AVVideoWidthKey:[NSNumber numberWithInt:480], // 必需
              AVVideoHeightKey:[NSNumber numberWithInt:320] // 必需
            }];
// 将其添加到AVAssetWriter
      [self.videoWriter addInput:self.videoInput];

- Satoshi Nakajima

Answer 1

这是我的做法；你选择的方法不支持后续对应用程序的扩展。与其不这样做，甚至牺牲更多时间和精力，还不如一开始就学会正确的方法。在我的应用程序中，在创建资产编写器后...

_writer = [[AVAssetWriter alloc] initWithURL:_outURL fileType:AVFileTypeQuickTimeMovie error:outError];

我创建了一个视频资产轨道...

 NSArray *videoTracks = [_asset tracksWithMediaType:AVMediaTypeVideo];
        if ([videoTracks count] > 0)
            assetVideoTrack = [videoTracks objectAtIndex:0];

然后从中创建一个资产读取器轨道输出对象：

_readerVideoOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:assetVideoTrack outputSettings:decompressionVideoSettings];
            [_reader addOutput:_readerVideoOutput];

然后，我将视频轨道的格式描述属性加载到一个数组中，当访问每个属性时，将每个元素转换为CMFormatDescriptionRef对象：

CMFormatDescriptionRef formatDescription = NULL;
NSArray *formatDescriptions = [assetVideoTrack formatDescriptions];
if ([formatDescriptions count] > 0)
    formatDescription = (__bridge CMFormatDescriptionRef)[formatDescriptions objectAtIndex:0];

然后，我尝试加载清晰光圈设置和像素宽高比设置，并在最后进行选择：

if (formatDescription)
            {
                NSDictionary *cleanAperture = nil;
                NSDictionary *pixelAspectRatio = nil;
                CFDictionaryRef cleanApertureFromCMFormatDescription = CMFormatDescriptionGetExtension(formatDescription, kCMFormatDescriptionExtension_CleanAperture);
                if (cleanApertureFromCMFormatDescription)
                {
                    cleanAperture = @{
                                      AVVideoCleanApertureWidthKey            : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureWidth),
                                      AVVideoCleanApertureHeightKey           : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureHeight),
                                      AVVideoCleanApertureHorizontalOffsetKey : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureHorizontalOffset),
                                      AVVideoCleanApertureVerticalOffsetKey   : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureVerticalOffset)
                                      };
                }
                CFDictionaryRef pixelAspectRatioFromCMFormatDescription = CMFormatDescriptionGetExtension(formatDescription, kCMFormatDescriptionExtension_PixelAspectRatio);
                if (pixelAspectRatioFromCMFormatDescription)
                {
                    pixelAspectRatio = @{
                                         AVVideoPixelAspectRatioHorizontalSpacingKey : (id)CFDictionaryGetValue(pixelAspectRatioFromCMFormatDescription, kCMFormatDescriptionKey_PixelAspectRatioHorizontalSpacing),
                                         AVVideoPixelAspectRatioVerticalSpacingKey   : (id)CFDictionaryGetValue(pixelAspectRatioFromCMFormatDescription, kCMFormatDescriptionKey_PixelAspectRatioVerticalSpacing)
                                         };
                }
                // Add whichever settings we could grab from the format description to the compression settings dictionary.
                if (cleanAperture || pixelAspectRatio)
                {
                    NSMutableDictionary *mutableCompressionSettings = [NSMutableDictionary dictionary];
                    if (cleanAperture)
                        [mutableCompressionSettings setObject:cleanAperture forKey:AVVideoCleanApertureKey];
                    if (pixelAspectRatio)
                        [mutableCompressionSettings setObject:pixelAspectRatio forKey:AVVideoPixelAspectRatioKey];
                    compressionSettings = mutableCompressionSettings;
                }
            }

那就是你混淆了；一些视频轨道只有其中一个，而另一些则没有，反之亦然。所以，你尝试同时加载它们，然后选择哪个属性集返回完整，并丢弃未返回的那个集合。

请记住，实际上只有一种方法可以嵌套所有要求的读写 iPhone 文件的方法，即使你看到很多变化。你能做的最明智和谨慎的事情就是确保你正在正确的方式下执行它。

如果你对此感兴趣，这就是它的样子：

#import "ExportVideo.h"

@implementation ExportVideo

@synthesize url = _url;
@synthesize renderer = _renderer;

- (id)initWithURL:(NSURL *)url usingRenderer:(GLKitView *)renderer {
    NSLog(@"ExportVideo");
    if (!(self = [super init])) {
        return nil;
    }

    self.url = url;
    self.renderer = renderer;

    NSString *serializationQueueDescription = [NSString stringWithFormat:@"%@ serialization queue", self];
    _mainSerializationQueue = dispatch_queue_create([serializationQueueDescription UTF8String], NULL);

    NSString *rwAudioSerializationQueueDescription = [NSString stringWithFormat:@"%@ rw audio serialization queue", self];
    _rwAudioSerializationQueue = dispatch_queue_create([rwAudioSerializationQueueDescription UTF8String], NULL);

    NSString *rwVideoSerializationQueueDescription = [NSString stringWithFormat:@"%@ rw video serialization queue", self];
    _rwVideoSerializationQueue = dispatch_queue_create([rwVideoSerializationQueueDescription UTF8String], NULL);

    return self;
}

- (void)startProcessing {
    NSDictionary *inputOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
    _asset = [[AVURLAsset alloc] initWithURL:self.url options:inputOptions];
    NSLog(@"URL: %@", self.url);
    _cancelled = NO;
    [_asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:@"tracks"] completionHandler: ^{
        dispatch_async(_mainSerializationQueue, ^{
            if (_cancelled)
                return;
            BOOL success = YES;
            NSError *localError = nil;
            success = ([_asset statusOfValueForKey:@"tracks" error:&localError] == AVKeyValueStatusLoaded);
            if (success)
            {
                NSFileManager *fm = [NSFileManager defaultManager];
                NSString *localOutputPath = [self.url path];
                if ([fm fileExistsAtPath:localOutputPath])
                    success = [fm removeItemAtPath:localOutputPath error:&localError];
            }
            if (success)
                success = [self setupAssetReaderAndAssetWriter:&localError];
            if (success)
                success = [self startAssetReaderAndWriter:&localError];
            if (!success)
                [self readingAndWritingDidFinishSuccessfully:success withError:localError];
        });
    }];
}


- (BOOL)setupAssetReaderAndAssetWriter:(NSError **)outError
{
    // Create and initialize the asset reader.
    _reader = [[AVAssetReader alloc] initWithAsset:_asset error:outError];
    BOOL success = (_reader != nil);
    if (success)
    {
        // If the asset reader was successfully initialized, do the same for the asset writer.
        NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
        _outputURL = paths[0];
        NSFileManager *manager = [NSFileManager defaultManager];
        [manager createDirectoryAtPath:_outputURL withIntermediateDirectories:YES attributes:nil error:nil];
        _outputURL = [_outputURL stringByAppendingPathComponent:@"output.mov"];
        [manager removeItemAtPath:_outputURL error:nil];
        _outURL = [NSURL fileURLWithPath:_outputURL];
        _writer = [[AVAssetWriter alloc] initWithURL:_outURL fileType:AVFileTypeQuickTimeMovie error:outError];
        success = (_writer != nil);
    }

    if (success)
    {
        // If the reader and writer were successfully initialized, grab the audio and video asset tracks that will be used.
        AVAssetTrack *assetAudioTrack = nil, *assetVideoTrack = nil;
        NSArray *audioTracks = [_asset tracksWithMediaType:AVMediaTypeAudio];
        if ([audioTracks count] > 0)
            assetAudioTrack = [audioTracks objectAtIndex:0];
        NSArray *videoTracks = [_asset tracksWithMediaType:AVMediaTypeVideo];
        if ([videoTracks count] > 0)
            assetVideoTrack = [videoTracks objectAtIndex:0];

        if (assetAudioTrack)
        {
            // If there is an audio track to read, set the decompression settings to Linear PCM and create the asset reader output.
            NSDictionary *decompressionAudioSettings = @{ AVFormatIDKey : [NSNumber numberWithUnsignedInt:kAudioFormatLinearPCM] };
            _readerAudioOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:assetAudioTrack outputSettings:decompressionAudioSettings];
            [_reader addOutput:_readerAudioOutput];
            // Then, set the compression settings to 128kbps AAC and create the asset writer input.
            AudioChannelLayout stereoChannelLayout = {
                .mChannelLayoutTag = kAudioChannelLayoutTag_Stereo,
                .mChannelBitmap = 0,
                .mNumberChannelDescriptions = 0
            };
            NSData *channelLayoutAsData = [NSData dataWithBytes:&stereoChannelLayout length:offsetof(AudioChannelLayout, mChannelDescriptions)];
            NSDictionary *compressionAudioSettings = @{
                                                       AVFormatIDKey         : [NSNumber numberWithUnsignedInt:kAudioFormatMPEG4AAC],
                                                       AVEncoderBitRateKey   : [NSNumber numberWithInteger:128000],
                                                       AVSampleRateKey       : [NSNumber numberWithInteger:44100],
                                                       AVChannelLayoutKey    : channelLayoutAsData,
                                                       AVNumberOfChannelsKey : [NSNumber numberWithUnsignedInteger:2]
                                                       };
            _writerAudioInput = [AVAssetWriterInput assetWriterInputWithMediaType:[assetAudioTrack mediaType] outputSettings:compressionAudioSettings];
            [_writer addInput:_writerAudioInput];
        }

        if (assetVideoTrack)
        {
            // If there is a video track to read, set the decompression settings for YUV and create the asset reader output.
            NSDictionary *decompressionVideoSettings = @{
                                                         (id)kCVPixelBufferPixelFormatTypeKey     : [NSNumber numberWithUnsignedInt:kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange],
                                                         (id)kCVPixelBufferIOSurfacePropertiesKey : [NSDictionary dictionary]
                                                         };
            _readerVideoOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:assetVideoTrack outputSettings:decompressionVideoSettings];
            [_reader addOutput:_readerVideoOutput];
            CMFormatDescriptionRef formatDescription = NULL;
            // Grab the video format descriptions from the video track and grab the first one if it exists.
            NSArray *formatDescriptions = [assetVideoTrack formatDescriptions];
            if ([formatDescriptions count] > 0)
                formatDescription = (__bridge CMFormatDescriptionRef)[formatDescriptions objectAtIndex:0];
            CGSize trackDimensions = {
                .width = 0.0,
                .height = 0.0,
            };
            // If the video track had a format description, grab the track dimensions from there. Otherwise, grab them direcly from the track itself.
            if (formatDescription)
                trackDimensions = CMVideoFormatDescriptionGetPresentationDimensions(formatDescription, false, false);
            else
                trackDimensions = [assetVideoTrack naturalSize];
            NSDictionary *compressionSettings = nil;
            // If the video track had a format description, attempt to grab the clean aperture settings and pixel aspect ratio used by the video.
            if (formatDescription)
            {
                NSDictionary *cleanAperture = nil;
                NSDictionary *pixelAspectRatio = nil;
                CFDictionaryRef cleanApertureFromCMFormatDescription = CMFormatDescriptionGetExtension(formatDescription, kCMFormatDescriptionExtension_CleanAperture);
                if (cleanApertureFromCMFormatDescription)
                {
                    cleanAperture = @{
                                      AVVideoCleanApertureWidthKey            : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureWidth),
                                      AVVideoCleanApertureHeightKey           : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureHeight),
                                      AVVideoCleanApertureHorizontalOffsetKey : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureHorizontalOffset),
                                      AVVideoCleanApertureVerticalOffsetKey   : (id)CFDictionaryGetValue(cleanApertureFromCMFormatDescription, kCMFormatDescriptionKey_CleanApertureVerticalOffset)
                                      };
                }
                CFDictionaryRef pixelAspectRatioFromCMFormatDescription = CMFormatDescriptionGetExtension(formatDescription, kCMFormatDescriptionExtension_PixelAspectRatio);
                if (pixelAspectRatioFromCMFormatDescription)
                {
                    pixelAspectRatio = @{
                                         AVVideoPixelAspectRatioHorizontalSpacingKey : (id)CFDictionaryGetValue(pixelAspectRatioFromCMFormatDescription, kCMFormatDescriptionKey_PixelAspectRatioHorizontalSpacing),
                                         AVVideoPixelAspectRatioVerticalSpacingKey   : (id)CFDictionaryGetValue(pixelAspectRatioFromCMFormatDescription, kCMFormatDescriptionKey_PixelAspectRatioVerticalSpacing)
                                         };
                }
                // Add whichever settings we could grab from the format description to the compression settings dictionary.
                if (cleanAperture || pixelAspectRatio)
                {
                    NSMutableDictionary *mutableCompressionSettings = [NSMutableDictionary dictionary];
                    if (cleanAperture)
                        [mutableCompressionSettings setObject:cleanAperture forKey:AVVideoCleanApertureKey];
                    if (pixelAspectRatio)
                        [mutableCompressionSettings setObject:pixelAspectRatio forKey:AVVideoPixelAspectRatioKey];
                    compressionSettings = mutableCompressionSettings;
                }
            }
            // Create the video settings dictionary for H.264.
            NSMutableDictionary *videoSettings = (NSMutableDictionary *) @{
                                                                           AVVideoCodecKey  : AVVideoCodecH264,
                                                                           AVVideoWidthKey  : [NSNumber numberWithDouble:trackDimensions.width],
                                                                           AVVideoHeightKey : [NSNumber numberWithDouble:trackDimensions.height]
                                                                           };
            // Put the compression settings into the video settings dictionary if we were able to grab them.
            if (compressionSettings)
                [videoSettings setObject:compressionSettings forKey:AVVideoCompressionPropertiesKey];
            // Create the asset writer input and add it to the asset writer.
            _writerVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:[assetVideoTrack mediaType] outputSettings:videoSettings];
            [_writer addInput:_writerVideoInput];
        }
    }
    return success;
}

- (BOOL)startAssetReaderAndWriter:(NSError **)outError
{
    BOOL success = YES;
    // Attempt to start the asset reader.
    success = [_reader startReading];
    if (!success) {
        *outError = [_reader error];
        NSLog(@"Reader error");
    }
    if (success)
    {
        // If the reader started successfully, attempt to start the asset writer.
        success = [_writer startWriting];
        if (!success) {
            *outError = [_writer error];
            NSLog(@"Writer error");
        }
    }

    if (success)
    {
        // If the asset reader and writer both started successfully, create the dispatch group where the reencoding will take place and start a sample-writing session.
        _dispatchGroup = dispatch_group_create();
        [_writer startSessionAtSourceTime:kCMTimeZero];
        _audioFinished = NO;
        _videoFinished = NO;

        if (_writerAudioInput)
        {
            // If there is audio to reencode, enter the dispatch group before beginning the work.
            dispatch_group_enter(_dispatchGroup);
            // Specify the block to execute when the asset writer is ready for audio media data, and specify the queue to call it on.
            [_writerAudioInput requestMediaDataWhenReadyOnQueue:_rwAudioSerializationQueue usingBlock:^{
                // Because the block is called asynchronously, check to see whether its task is complete.
                if (_audioFinished)
                    return;
                BOOL completedOrFailed = NO;
                // If the task isn't complete yet, make sure that the input is actually ready for more media data.
                while ([_writerAudioInput isReadyForMoreMediaData] && !completedOrFailed)
                {
                    // Get the next audio sample buffer, and append it to the output file.
                    CMSampleBufferRef sampleBuffer = [_readerAudioOutput copyNextSampleBuffer];
                    if (sampleBuffer != NULL)
                    {
                        BOOL success = [_writerAudioInput appendSampleBuffer:sampleBuffer];
                        CFRelease(sampleBuffer);
                        sampleBuffer = NULL;
                        completedOrFailed = !success;
                    }
                    else
                    {
                        completedOrFailed = YES;
                    }
                }
                if (completedOrFailed)
                {
                    // Mark the input as finished, but only if we haven't already done so, and then leave the dispatch group (since the audio work has finished).
                    BOOL oldFinished = _audioFinished;
                    _audioFinished = YES;
                    if (oldFinished == NO)
                    {
                        [_writerAudioInput markAsFinished];
                    }
                    dispatch_group_leave(_dispatchGroup);
                }
            }];
        }

        if (_writerVideoInput)
        {
            // If we had video to reencode, enter the dispatch group before beginning the work.
            dispatch_group_enter(_dispatchGroup);
            // Specify the block to execute when the asset writer is ready for video media data, and specify the queue to call it on.
            [_writerVideoInput requestMediaDataWhenReadyOnQueue:_rwVideoSerializationQueue usingBlock:^{
                // Because the block is called asynchronously, check to see whether its task is complete.
                if (_videoFinished)
                    return;
                BOOL completedOrFailed = NO;
                // If the task isn't complete yet, make sure that the input is actually ready for more media data.
                while ([_writerVideoInput isReadyForMoreMediaData] && !completedOrFailed)
                {
                    // Get the next video sample buffer, and append it to the output file.
                    CMSampleBufferRef sampleBuffer = [_readerVideoOutput copyNextSampleBuffer];

                    /* PROCESS FRAME HERE */
                    //CVImageBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
                    //_currentBuffer = pixelBuffer;
                    //[self performSelectorOnMainThread:@selector(processFrame) withObject:nil waitUntilDone:YES];
                    /* ------------------ */

                    if (sampleBuffer != NULL)
                    {
                        BOOL success = [_writerVideoInput appendSampleBuffer:sampleBuffer];
                        CFRelease(sampleBuffer);
                        sampleBuffer = NULL;
                        completedOrFailed = !success;
                    }
                    else
                    {
                        completedOrFailed = YES;
                    }
                }
                if (completedOrFailed)
                {
                    // Mark the input as finished, but only if we haven't already done so, and then leave the dispatch group (since the video work has finished).
                    BOOL oldFinished = _videoFinished;
                    _videoFinished = YES;
                    if (oldFinished == NO)
                    {
                        [_writerVideoInput markAsFinished];
                    }
                    dispatch_group_leave(_dispatchGroup);
                }
            }];
        }
        // Set up the notification that the dispatch group will send when the audio and video work have both finished.
        dispatch_group_notify(_dispatchGroup, _mainSerializationQueue, ^{
            BOOL finalSuccess = YES;
            NSError *finalError = nil;
            // Check to see if the work has finished due to cancellation.
            if (_cancelled)
            {
                // If so, cancel the reader and writer.
                [_reader cancelReading];
                [_writer cancelWriting];
            }
            else
            {
                // If cancellation didn't occur, first make sure that the asset reader didn't fail.
                if ([_reader status] == AVAssetReaderStatusFailed)
                {
                    finalSuccess = NO;
                    finalError = [_reader error];
                    NSLog(@"_reader finalError: %@", finalError);
                }
                // If the asset reader didn't fail, attempt to stop the asset writer and check for any errors.
                [_writer finishWritingWithCompletionHandler:^{
                    UISaveVideoAtPathToSavedPhotosAlbum(_outputURL, nil, nil, nil);
                    [self readingAndWritingDidFinishSuccessfully:finalSuccess withError:[_writer error]];
                }];
            }
            // Call the method to handle completion, and pass in the appropriate parameters to indicate whether reencoding was successful.

        });
    }
    // Return success here to indicate whether the asset reader and writer were started successfully.
    return success;
}

- (void)readingAndWritingDidFinishSuccessfully:(BOOL)success withError:(NSError *)error
{
    if (!success)
    {
        // If the reencoding process failed, we need to cancel the asset reader and writer.
        [_reader cancelReading];
        [_writer cancelWriting];
        dispatch_async(dispatch_get_main_queue(), ^{
            // Handle any UI tasks here related to failure.
        });
    }
    else
    {
        // Reencoding was successful, reset booleans.
        _cancelled = NO;
        _videoFinished = NO;
        _audioFinished = NO;
        dispatch_async(dispatch_get_main_queue(), ^{
            // Handle any UI tasks here related to success.
        });
    }
    NSLog(@"readingAndWritingDidFinishSuccessfully success = %@ : Error = %@", (success == 0) ? @"NO" : @"YES", error);
}

@end

- James Bush

---

我如何在现有的AVAsset中使用它？谢谢！ - trdavidson

Answer 2

解决方法之一是使用固定大小的AVCaptureSessionPresets之一，例如AVCaptureSessionPreset640x480。在开始捕获之前，似乎没有公共API可以获取AVCaptureSession分辨率：

了解AVCaptureSession的会话预设的分辨率

- Tark

Answer 3

谢谢您的快速回答，Tark。根据您的答案，我决定推迟创建AVAssetWriterInput直到第一帧，效果非常好。以下是代码。

    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    CVPixelBufferLockBaseAddress(imageBuffer, 0);
    size_t width = CVPixelBufferGetWidth(imageBuffer);
    size_t height = CVPixelBufferGetHeight(imageBuffer);
    CVPixelBufferUnlockBaseAddress(imageBuffer,0);
    NSLog(@"NVW size=%zd, %zd", width, height);
NSDictionary* compression = @{
        AVVideoAverageBitRateKey:[NSNumber numberWithInt:960000],
        AVVideoMaxKeyFrameIntervalKey:[NSNumber numberWithInt:1]
    };
    self.videoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo
        outputSettings:@{
            AVVideoCodecKey:AVVideoCodecH264,
            AVVideoCompressionPropertiesKey:compression,
            AVVideoWidthKey:[NSNumber numberWithInt:width],
            AVVideoHeightKey:[NSNumber numberWithInt:height]
        }];
    self.videoInput.expectsMediaDataInRealTime = YES;

- Satoshi Nakajima