導(dǎo)出音視頻文件
要讀取和寫入視聽asset，必須使用AVFoundation框架中的導(dǎo)出api。AVAssetExportSession類僅是一個簡單的導(dǎo)出的接口，例如修改文件格式或者修剪資源的長度。想要更多的導(dǎo)出需求，我們需要是用AVAssetReader類和AVAssetWriter類
如果想要對asset中的內(nèi)容操作，那么使用AVAssetReader類。例如，讀取asset的track以產(chǎn)生波形的只管表示。要從樣本緩沖區(qū)或者靜止圖像等媒體生成asset，使用AVAssetWriter類
注意：asset的讀取和編寫不能用于實時處理。實際上，AVAssetReader不能用于http實時流等實時源讀取。但是，我們可以使用AVAssetWriter對實時數(shù)據(jù)（例如AVCaptureOutput對象）進行處理。我們需要設(shè)置expectsMediaDataInRealTime=yes。對于非實時性源數(shù)據(jù)，將此屬性設(shè)置為yes，將導(dǎo)致文件無法正確存取。
讀取asset
每個AVAssetReader對象一次只能與一個asset相關(guān)聯(lián)，但是asset可以包含多個track。因此，在開始讀取asset之前，我們必須要將AVAssetReaderOutput類的具體子類分配給AVAssetReader對象，以便配置媒體數(shù)據(jù)的讀取方式。AVAssetReaderOutput基類有三個具體的子類，可以滿足讀取asset的要求。他們是AVAssetReaderTrackOutput，AVAssetReaderAudioMixOutput和AVAssetReaderVideoCompositionOutput。
具體關(guān)系如圖
創(chuàng)建asset的閱讀器 -AVAssetReader
NSError *outError;
AVAsset *someAsset = <#AVAsset that you want to read#>;
AVAssetReader *assetReader = [AVAssetReader assetReaderWithAsset:someAsset error:&outError];
BOOL success = (assetReader != nil)
注意：這里必須檢測AVAssetReader實例對象是否真正的生成。error包含沒有生成的錯誤信息
設(shè)置 AVAssetReaderOutput
創(chuàng)建AVAssetReader后，我們應(yīng)該設(shè)置一個輸出。當(dāng)我們設(shè)置輸出后，確保alwaysCopiesSampleData屬性是NO。通過這種方式，我們可以獲得性能改進的好處。
如果只想從一個或者多個track讀取媒體數(shù)據(jù)，并轉(zhuǎn)換數(shù)據(jù)為其他格式，那么我們應(yīng)該使用AVAssetReaderTrackOutput類，該類可以從asset中讀取每個AVAssetTrack對象。如果想壓縮一個音頻track成 linear pcm，我們應(yīng)該如下設(shè)置
AVAsset *localAsset = assetReader.asset;
// Get the audio track to read.
AVAssetTrack *audioTrack = [[localAsset tracksWithMediaType:AVMediaTypeAudio] objectAtIndex:0];
// Decompression settings for Linear PCM
NSDictionary *decompressionAudioSettings = @{ AVFormatIDKey : [NSNumber numberWithUnsignedInt:kAudioFormatLinearPCM] };
// Create the output with the audio track and decompression settings.
AVAssetReaderOutput *trackOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:audioTrack outputSettings:decompressionAudioSettings];
// Add the output to the reader if possible.
if ([assetReader canAddOutput:trackOutput])
[assetReader addOutput:trackOutput];
注意，這里要是把audioSettings傳遞為nil，那么就是告訴assetReader以最方便的未壓縮格式返回樣本。
視頻合成輸出的行為方式大致相同：我們可以使用AVVideoComposition對象從asset中讀取多個track。從多個AVVideoComposition 的track中讀取媒體數(shù)據(jù)并將其解壓縮為ARGB。方式如下
AVVideoComposition *videoComposition = <#An AVVideoComposition that specifies how the video tracks from the AVAsset are composited#>;
// Assumes assetReader was initialized with an AVComposition.
AVComposition *composition = (AVComposition *)assetReader.asset;
// Get the video tracks to read.
NSArray *videoTracks = [composition tracksWithMediaType:AVMediaTypeVideo];
// Decompression settings for ARGB.
NSDictionary *decompressionVideoSettings = @{ (id)kCVPixelBufferPixelFormatTypeKey : [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32ARGB], (id)kCVPixelBufferIOSurfacePropertiesKey : [NSDictionary dictionary] };
// Create the video composition output with the video tracks and decompression setttings.
AVAssetReaderOutput *videoCompositionOutput = [AVAssetReaderVideoCompositionOutput assetReaderVideoCompositionOutputWithVideoTracks:videoTracks videoSettings:decompressionVideoSettings];
// Associate the video composition used to composite the video tracks being read with the output.
videoCompositionOutput.videoComposition = videoComposition;
// Add the output to the reader if possible.
if ([assetReader canAddOutput:videoCompositionOutput])
[assetReader addOutput:videoCompositionOutput];
讀取asset的媒體數(shù)據(jù)
在設(shè)置所需的所有輸出后開始讀取asset，我們應(yīng)該調(diào)用startReading方法。接下來，使用copyNextSampleBuffer方法從每個輸出中單獨檢索媒體數(shù)據(jù)。要是使用單個輸出啟動assert reader并讀取所有的媒體，請看下列例子：
// Start the asset reader up.
[self.assetReader startReading];
BOOL done = NO;
while (!done)
{
// Copy the next sample buffer from the reader output.
CMSampleBufferRef sampleBuffer = [self.assetReaderOutput copyNextSampleBuffer];
if (sampleBuffer)
{
// Do something with sampleBuffer here.
CFRelease(sampleBuffer);
sampleBuffer = NULL;
}
else
{
// Find out why the asset reader output couldn't copy another sample buffer.
if (self.assetReader.status == AVAssetReaderStatusFailed)
{
NSError *failureError = self.assetReader.error;
// Handle the error here.
}
else
{
// The asset reader output has read all of its samples.
done = YES;
}
}
}
寫asset
AVAssetWriter 類可以將多個源的媒體數(shù)據(jù)寫入指定文件格式的單個文件。我們不需要將AVAssetWriter和asset聯(lián)系在一起，但是需要有輸出文件與之對應(yīng)。這是因為AVAssetWriter可以使用多個源寫入媒體數(shù)據(jù)，因此我們必須要為每個單獨的track創(chuàng)建AVAssetWriterInput對象。每一個AVAssetWriterInput對象都已CMSampleBufferRef對象的形式接受數(shù)據(jù)，如果想要追加數(shù)據(jù)到CVPixelBufferRef對象上，應(yīng)該使用AVAssetWriterInputPixelBufferAdaptor類。
創(chuàng)建AVAssetWriter對象
創(chuàng)建AVAssetWriter對象，我們需要指定一個輸出路徑的url。
NSError *outError;
NSURL *outputURL = <#NSURL object representing the URL where you want to save the video#>;
AVAssetWriter *assetWriter = [AVAssetWriter assetWriterWithURL:outputURL
fileType:AVFileTypeQuickTimeMovie
error:&outError];
BOOL success = (assetWriter != nil);
設(shè)置asset的 輸入源
使用AVAssetWriter對象可以寫入媒體數(shù)據(jù)，我們必須至少設(shè)置一個輸入源。例如，我們將媒體數(shù)據(jù)轉(zhuǎn)換成了CMSampleBufferRef對象，那么我們只需要使用AVAssetWriterInput類即可。要設(shè)置將音頻媒體數(shù)據(jù)壓縮為128kbps aac 并將其連接到AVAssetWriter ，步驟如下
// Configure the channel layout as stereo.
AudioChannelLayout stereoChannelLayout = {
.mChannelLayoutTag = kAudioChannelLayoutTag_Stereo,
.mChannelBitmap = 0,
.mNumberChannelDescriptions = 0
};
// Convert the channel layout object to an NSData object.
NSData *channelLayoutAsData = [NSData dataWithBytes:&stereoChannelLayout length:offsetof(AudioChannelLayout, mChannelDescriptions)];
// Get the compression settings for 128 kbps AAC.
NSDictionary *compressionAudioSettings = @{
AVFormatIDKey : [NSNumber numberWithUnsignedInt:kAudioFormatMPEG4AAC],
AVEncoderBitRateKey : [NSNumber numberWithInteger:128000],
AVSampleRateKey : [NSNumber numberWithInteger:44100],
AVChannelLayoutKey : channelLayoutAsData,
AVNumberOfChannelsKey : [NSNumber numberWithUnsignedInteger:2]
};
// Create the asset writer input with the compression settings and specify the media type as audio.
AVAssetWriterInput *assetWriterInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeAudio outputSettings:compressionAudioSettings];
// Add the input to the writer if possible.
if ([assetWriter canAddInput:assetWriterInput])
[assetWriter addInput:assetWriterInput];
注意：如果要以存儲的格式寫入媒體數(shù)據(jù)，請在outputSettings傳遞nil。僅當(dāng)使用fileType為AVFileTypeQuickTimeMovie初始化才傳遞為nil。
如果asset writer的input 可以選擇性的包含一些元數(shù)據(jù)，或者分別使用元數(shù)據(jù)和transform屬性為特定的track指定不同的transfrom。對于將數(shù)據(jù)源是一個視頻track的asset writer的input，我們可以通過執(zhí)行下列操作維護視頻的原始transform。
AVAsset *videoAsset = <#AVAsset with at least one video track#>;
AVAssetTrack *videoAssetTrack = [[videoAsset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
assetWriterInput.transform = videoAssetTrack.preferredTransform;
注意：metadata 和transform 屬性要在啟動AVAssetWriter之前開啟。
將媒體數(shù)據(jù)寫入到輸出文件時，有時候可能需要分配像素緩沖區(qū)。因此，使用AVAssetWriterInputPixelBufferAdaptor類。為了獲取最高效率，我們應(yīng)該提供一個緩沖池。看下列代碼
NSDictionary *pixelBufferAttributes = @{
kCVPixelBufferCGImageCompatibilityKey : [NSNumber numberWithBool:YES],
kCVPixelBufferCGBitmapContextCompatibilityKey : [NSNumber numberWithBool:YES],
kCVPixelBufferPixelFormatTypeKey : [NSNumber numberWithInt:kCVPixelFormatType_32ARGB]
};
AVAssetWriterInputPixelBufferAdaptor *inputPixelBufferAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:self.assetWriterInput sourcePixelBufferAttributes:pixelBufferAttributes];
所有的AVAssetWriterInputPixelBufferAdaptor和一個asset 的input關(guān)聯(lián)。并且intput必須是AVMediaTypeVideo類型的媒體數(shù)據(jù)
編寫媒體數(shù)據(jù)
當(dāng)我們?yōu)锳VAssetWriter配置所有的inputs 時，我們就可以編寫媒體數(shù)據(jù)了。通過調(diào)用startWriting方法啟動寫入數(shù)據(jù)。然后需要調(diào)用startSessionAtSourceTime：方法來啟動編寫會話。每個媒體數(shù)據(jù)都有個時間范圍，AVAssetWriter通過這個來一次編寫input?？聪铝欣樱?/p>
CMTime halfAssetDuration = CMTimeMultiplyByFloat64(self.asset.duration, 0.5);
[self.assetWriter startSessionAtSourceTime:halfAssetDuration];
//Implementation continues.
通過，要結(jié)束寫的session，我們必須調(diào)用endSessionAtSourceTime方法。但是，如果我們寫的session已經(jīng)寫到文件末尾了，只需要調(diào)用finishWriting即可。
// Prepare the asset writer for writing.
[self.assetWriter startWriting];
// Start a sample-writing session.
[self.assetWriter startSessionAtSourceTime:kCMTimeZero];
// Specify the block to execute when the asset writer is ready for media data and the queue to call it on.
[self.assetWriterInput requestMediaDataWhenReadyOnQueue:myInputSerialQueue usingBlock:^{
while ([self.assetWriterInput isReadyForMoreMediaData])
{
// Get the next sample buffer.
CMSampleBufferRef nextSampleBuffer = [self copyNextSampleBufferToWrite];
if (nextSampleBuffer)
{
// If it exists, append the next sample buffer to the output file.
[self.assetWriterInput appendSampleBuffer:nextSampleBuffer];
CFRelease(nextSampleBuffer);
nextSampleBuffer = nil;
}
else
{
// Assume that lack of a next sample buffer means the sample buffer source is out of samples and mark the input as finished.
[self.assetWriterInput markAsFinished];
break;
}
}
}];
重新編碼assets
我們可以串聯(lián) AVAssetReader 和AVAssetWriter，將asset從一種表示轉(zhuǎn)換成另一種表示。使用這些對象，我們可以比使用AVAssetExportSession對象更多的控制轉(zhuǎn)換。例如，我們可以選擇要在輸出文件中表示那些軌道，指定自己的輸出格式，或者在轉(zhuǎn)換過程中修改asset。此過程的第一步是根據(jù)需要設(shè)置
AVAssetReader和AVAssetWriter 的input。當(dāng)AVAssetReader和AVAssetWriter完全配置完畢后，，分別調(diào)用startReading和startWriting方法啟動它們?？聪铝写a
NSString *serializationQueueDescription = [NSString stringWithFormat:@"%@ serialization queue", self];
// Create a serialization queue for reading and writing.
dispatch_queue_t serializationQueue = dispatch_queue_create([serializationQueueDescription UTF8String], NULL);
// Specify the block to execute when the asset writer is ready for media data and the queue to call it on.
[self.assetWriterInput requestMediaDataWhenReadyOnQueue:serializationQueue usingBlock:^{
while ([self.assetWriterInput isReadyForMoreMediaData])
{
// Get the asset reader output's next sample buffer.
CMSampleBufferRef sampleBuffer = [self.assetReaderOutput copyNextSampleBuffer];
if (sampleBuffer != NULL)
{
// If it exists, append this sample buffer to the output file.
BOOL success = [self.assetWriterInput appendSampleBuffer:sampleBuffer];
CFRelease(sampleBuffer);
sampleBuffer = NULL;
// Check for errors that may have occurred when appending the new sample buffer.
if (!success && self.assetWriter.status == AVAssetWriterStatusFailed)
{
NSError *failureError = self.assetWriter.error;
//Handle the error.
}
}
else
{
// If the next sample buffer doesn't exist, find out why the asset reader output couldn't vend another one.
if (self.assetReader.status == AVAssetReaderStatusFailed)
{
NSError *failureError = self.assetReader.error;
//Handle the error here.
}
else
{
// The asset reader output must have vended all of its samples. Mark the input as finished.
[self.assetWriterInput markAsFinished];
break;
}
}
}
}];
export 真是匯總demo
上面都是知識片段，看知識片段還不能完全了解具體的使用，我們下列就具體的編寫一個demo來看看
demo的具體步驟如下
- 1.使用串行隊列異步處理讀取和寫入的視聽數(shù)據(jù)
- 2.初始化AVAssetReader對象，配置兩個output，一個視頻另一個音頻
- 3.初始化AVASsetWriter對象，配置兩個inputs，一個音頻一個視頻
- 4.使用AVAssetReader對象異步將獲取的數(shù)據(jù)傳輸給AVASsetWriter對象
- 5.用dispatch goupe通知重新編碼過程的完成。
- 6允許用戶在開始后取消重新編碼過程
強制引用屬性
@property (nonatomic,strong) AVCaptureSession * captureSession;
@property (nonatomic,strong) dispatch_queue_t mainSerializationQueue;
@property (nonatomic,strong) dispatch_queue_t rwAudioSerializationQueue;
@property (nonatomic,strong) dispatch_queue_t rwVideoSerializationQueue;
@property (nonatomic,strong) AVURLAsset *asset;
@property (nonatomic,strong) NSURL *outputURL;
@property (nonatomic,assign) BOOL cancelled;
@property (nonatomic,strong) AVAssetReader *assetReader;
@property (nonatomic,strong) AVAssetWriter *assetWriter;
@property (nonatomic,strong) AVAssetReaderTrackOutput *assetReaderAudioOutput;
@property (nonatomic,strong) AVAssetWriterInput *assetWriterAudioInput;
@property (nonatomic,strong) AVAssetReaderTrackOutput *assetReaderVideoOutput;
@property (nonatomic,strong) AVAssetWriterInput *assetWriterVideoInput;
@property (nonatomic,strong) dispatch_group_t dispatchGroup;
@property (nonatomic,assign) BOOL audioFinished;
@property (nonatomic,assign) BOOL videoFinished;
-(AVURLAsset * )getAVAssetABC{
NSURL *fileURL = [[NSBundle mainBundle] URLForResource:@"abc" withExtension:@"mp4"];
AVURLAsset * asset = [AVURLAsset URLAssetWithURL:fileURL options:nil];
return asset;
}
- (void)viewDidLoad {
[super viewDidLoad];
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES);
NSString *path = [[[paths objectAtIndex:0]stringByAppendingPathComponent:[NSUUID UUID].UUIDString] stringByAppendingString:@".mov"];
self.path = path;
NSLog(@"%@",self.path);
// [self edit];
// [self capture];
[self readerWriter];
}
-(void)readerWriter{
NSString *serializationQueueDescription = [NSString stringWithFormat:@"%@ serialization queue", self];
// Create the main serialization queue.
self.mainSerializationQueue = dispatch_queue_create([serializationQueueDescription UTF8String], NULL);
NSString *rwAudioSerializationQueueDescription = [NSString stringWithFormat:@"%@ rw audio serialization queue", self];
// Create the serialization queue to use for reading and writing the audio data.
self.rwAudioSerializationQueue = dispatch_queue_create([rwAudioSerializationQueueDescription UTF8String], NULL);
NSString *rwVideoSerializationQueueDescription = [NSString stringWithFormat:@"%@ rw video serialization queue", self];
// Create the serialization queue to use for reading and writing the video data.
self.rwVideoSerializationQueue = dispatch_queue_create([rwVideoSerializationQueueDescription UTF8String], NULL);
self.asset = [self getAVAssetABC];
self.cancelled = NO;
self.outputURL = [NSURL fileURLWithPath:self.path];;
[self.asset loadValuesAsynchronouslyForKeys:@[@"tracks"] completionHandler:^{
// Once the tracks have finished loading, dispatch the work to the main serialization queue.
dispatch_async(self.mainSerializationQueue, ^{
// Due to asynchronous nature, check to see if user has already cancelled.
if (self.cancelled)
return;
BOOL success = YES;
NSError *localError = nil;
// Check for success of loading the assets tracks.
success = ([self.asset statusOfValueForKey:@"tracks" error:&localError] == AVKeyValueStatusLoaded);
if (success)
{
// If the tracks loaded successfully, make sure that no file exists at the output path for the asset writer.
NSFileManager *fm = [NSFileManager defaultManager];
NSString *localOutputPath = [self.outputURL 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
{
self.assetReader = [[AVAssetReader alloc] initWithAsset:self.asset error:outError];
BOOL success = (self.assetReader != nil);
if (success)
{
// If the asset reader was successfully initialized, do the same for the asset writer.
self.assetWriter = [[AVAssetWriter alloc] initWithURL:self.outputURL fileType:AVFileTypeQuickTimeMovie error:outError];
success = (self.assetWriter != 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 = [self.asset tracksWithMediaType:AVMediaTypeAudio];
if ([audioTracks count] > 0)
assetAudioTrack = [audioTracks objectAtIndex:0];
NSArray *videoTracks = [self.asset tracksWithMediaType:AVMediaTypeVideo];
if ([videoTracks count] > 0)
assetVideoTrack = [videoTracks objectAtIndex:0];
///音頻輸入和輸出
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] };
self.assetReaderAudioOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:assetAudioTrack outputSettings:decompressionAudioSettings];
[self.assetReader addOutput:self.assetReaderAudioOutput];
// 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]
};
self.assetWriterAudioInput = [AVAssetWriterInput assetWriterInputWithMediaType:[assetAudioTrack mediaType] outputSettings:compressionAudioSettings];
[self.assetWriter addInput:self.assetWriterAudioInput];
}
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_422YpCbCr8],
(id)kCVPixelBufferIOSurfacePropertiesKey : [NSDictionary dictionary]
};
self.assetReaderVideoOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:assetVideoTrack outputSettings:decompressionVideoSettings];
[self.assetReader addOutput:self.assetReaderVideoOutput];
CMFormatDescriptionRef formatDescription = NULL;
// Grab the video format descriptions from the video track and grab the first one if it exists.
NSArray *videoFormatDescriptions = [assetVideoTrack formatDescriptions];
if ([videoFormatDescriptions count] > 0)
formatDescription = (__bridge CMFormatDescriptionRef)[videoFormatDescriptions 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 *videos = (NSMutableDictionary *) @{
AVVideoCodecKey : AVVideoCodecH264,
AVVideoWidthKey : [NSNumber numberWithDouble:trackDimensions.width],
AVVideoHeightKey : [NSNumber numberWithDouble:trackDimensions.height]
};
NSMutableDictionary * videoSettings = [NSMutableDictionary dictionary];
[videoSettings setDictionary:videos];
// 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.
self.assetWriterVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:[assetVideoTrack mediaType] outputSettings:videoSettings];
[self.assetWriter addInput:self.assetWriterVideoInput];
}
}
return success;
}
- (BOOL)startAssetReaderAndWriter:(NSError **)outError
{
BOOL success = YES;
// Attempt to start the asset reader.
success = [self.assetReader startReading];
if (!success)
*outError = [self.assetReader error];
if (success)
{
// If the reader started successfully, attempt to start the asset writer.
success = [self.assetWriter startWriting];
if (!success)
*outError = [self.assetWriter 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.
self.dispatchGroup = dispatch_group_create();
[self.assetWriter startSessionAtSourceTime:kCMTimeZero];
self.audioFinished = NO;
self.videoFinished = NO;
if (self.assetWriterAudioInput)
{
// If there is audio to reencode, enter the dispatch group before beginning the work.
dispatch_group_enter(self.dispatchGroup);
// Specify the block to execute when the asset writer is ready for audio media data, and specify the queue to call it on.
[self.assetWriterAudioInput requestMediaDataWhenReadyOnQueue:self.rwAudioSerializationQueue usingBlock:^{
// Because the block is called asynchronously, check to see whether its task is complete.
if (self.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 ([self.assetWriterAudioInput isReadyForMoreMediaData] && !completedOrFailed)
{
// Get the next audio sample buffer, and append it to the output file.
CMSampleBufferRef sampleBuffer = [self.assetReaderAudioOutput copyNextSampleBuffer];
if (sampleBuffer != NULL)
{
BOOL success = [self.assetWriterAudioInput 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 = self.audioFinished;
self.audioFinished = YES;
if (oldFinished == NO)
{
[self.assetWriterAudioInput markAsFinished];
}
dispatch_group_leave(self.dispatchGroup);
}
}];
}
if (self.assetWriterVideoInput)
{
// If we had video to reencode, enter the dispatch group before beginning the work.
dispatch_group_enter(self.dispatchGroup);
// Specify the block to execute when the asset writer is ready for video media data, and specify the queue to call it on.
[self.assetWriterVideoInput requestMediaDataWhenReadyOnQueue:self.rwVideoSerializationQueue usingBlock:^{
// Because the block is called asynchronously, check to see whether its task is complete.
if (self.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 ([self.assetWriterVideoInput isReadyForMoreMediaData] && !completedOrFailed)
{
// Get the next video sample buffer, and append it to the output file.
CMSampleBufferRef sampleBuffer = [self.assetReaderVideoOutput copyNextSampleBuffer];
if (sampleBuffer != NULL)
{
BOOL success = [self.assetWriterVideoInput 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 = self.videoFinished;
self.videoFinished = YES;
if (oldFinished == NO)
{
[self.assetWriterVideoInput markAsFinished];
}
dispatch_group_leave(self.dispatchGroup);
}
}];
}
// Set up the notification that the dispatch group will send when the audio and video work have both finished.
dispatch_group_notify(self.dispatchGroup, self.mainSerializationQueue, ^{
BOOL finalSuccess = YES;
NSError *finalError = nil;
// Check to see if the work has finished due to cancellation.
if (self.cancelled)
{
// If so, cancel the reader and writer.
[self.assetReader cancelReading];
[self.assetWriter cancelWriting];
}
else
{
// If cancellation didn't occur, first make sure that the asset reader didn't fail.
if ([self.assetReader status] == AVAssetReaderStatusFailed)
{
finalSuccess = NO;
finalError = [self.assetReader error];
}
// If the asset reader didn't fail, attempt to stop the asset writer and check for any errors.
if (finalSuccess)
{
finalSuccess = [self.assetWriter finishWriting];
if (!finalSuccess)
finalError = [self.assetWriter error];
}
}
// Call the method to handle completion, and pass in the appropriate parameters to indicate whether reencoding was successful.
[self readingAndWritingDidFinishSuccessfully:finalSuccess withError:finalError];
});
}
// Return success here to indicate whether the asset reader and writer were started successfully.
return success;
}
