第五十七篇AVAssetReader和AVAssetWrite 对视频进行编码
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AV Foundation提供了直接处理媒体样本的低级功能，其中需要使用的两个重要的类，AVAssetReader和AVAssetWrite，AVAssetReader用于从AVAsset资源读取媒体样本，AVAssetWrite用于对媒体资源进行编码并写入到容器文件中。下面简单的使用一下：
初始化AVAssetReader
-(void)configAssetReader { NSURL *videoUrl = [NSURL fileURLWithPath:[self resoucePath]]; _asset = [AVAsset assetWithURL:videoUrl]; //获取资源的一个视频轨道 AVAssetTrack *track = [[_asset tracksWithMediaType:AVMediaTypeVideo] firstObject]; _assetReader = [[AVAssetReader alloc] initWithAsset:_asset error:nil]; //指定将读取的样本数据压缩为BGRA格式 NSDictionary *setting = @{(id)kCVPixelBufferPixelFormatTypeKey:@(kCVPixelFormatType_32BGRA)}; //初始化输出，指定从track轨道中读取样本数据 _assetOutPut = [[AVAssetReaderTrackOutput alloc] initWithTrack:track outputSettings:setting]; //添加输出 [_assetReader addOutput:_assetOutPut]; //开始读取过程 [_assetReader startReading]; }
初始化AVAssetWrite
-(void)configWriteInput { NSString *storePath = nil; NSString *path = [self resoucePath]; NSRange range = [path rangeOfString:@"/" options:NSBackwardsSearch]; if (range.location != NSNotFound) { NSString *pathRoot = [path substringToIndex:range.location]; storePath = [pathRoot stringByAppendingPathComponent:@"copy.mp4"]; } if (storePath) { _assetWrite = [[AVAssetWriter alloc] initWithURL:[NSURL fileURLWithPath:storePath] fileType:AVFileTypeQuickTimeMovie error:nil]; //指定编码格式，像素宽高等信息 NSDictionary *setting = @{ AVVideoCodecKey:AVVideoCodecH264, AVVideoWidthKey:@1280, AVVideoHeightKey:@720, AVVideoCompressionPropertiesKey:@{ AVVideoMaxKeyFrameIntervalKey:@1, AVVideoAverageBitRateKey:@10500000, AVVideoProfileLevelKey:AVVideoProfileLevelH264Main31 } }; 初始化写入器，并制定了媒体格式 _assetInput = [[AVAssetWriterInput alloc] initWithMediaType:AVMediaTypeVideo outputSettings:setting]; //添加写入器 [_assetWrite addInput:_assetInput]; [_assetWrite startWriting]; } }
将读取的数据写入到_assetInput写入器中
-(void)assertReadToAssetInput { dispatch_queue_t queue = dispatch_queue_create("com.writequeue", DISPATCH_QUEUE_CONCURRENT); if (_assetInput) { __block NSInteger count = 0; __block BOOL isComplete = NO; //开启写入会话，并指定样本的开始时间 [_assetWrite startSessionAtSourceTime:kCMTimeZero]; [_assetInput requestMediaDataWhenReadyOnQueue:queue usingBlock:^{ if (!isComplete && _assetInput.readyForMoreMediaData) { //样本数据 CMSampleBufferRef buffer = [_assetOutPut copyNextSampleBuffer]; if (buffer) { [_assetInput appendSampleBuffer:buffer]; count++; // 展示第2000帧数据 if (count == 2000) { CGImageRef imgref = [UIImage imageFromSampleBufferRef:buffer]; //读取CMSampleBuffer中的数据，将其转化为CGImageRef 参考代码见：http://www.jianshu.com/p/3d5ccbde0de1 UIImage *img = [UIImage imageWithCGImage:imgref]; dispatch_sync(dispatch_get_main_queue(), ^{ _imageView.image = img; }); } } else { isComplete = YES; } if(isComplete) { //关闭写入会话 [_assetWrite finishWritingWithCompletionHandler:^{ AVAssetWriterStatus status = self.assetWrite.status; if (status == AVAssetWriterStatusCompleted) { NSLog(@"finsished"); } else { NSLog(@"failure"); } }]; } } }]; } }
-(void)assertReadToAssetInput { dispatch_queue_t queue = dispatch_queue_create("com.writequeue", DISPATCH_QUEUE_CONCURRENT); if (_assetInput) { __block NSInteger count = 0; __block BOOL isComplete = NO; //开启写入会话，并指定样本的开始时间 [_assetWrite startSessionAtSourceTime:kCMTimeZero]; [_assetInput requestMediaDataWhenReadyOnQueue:queue usingBlock:^{ if (!isComplete && _assetInput.readyForMoreMediaData) { //样本数据 CMSampleBufferRef buffer = [_assetOutPut copyNextSampleBuffer]; if (buffer) { [_assetInput appendSampleBuffer:buffer]; count++; // 展示第2000帧数据 if (count == 2000) { CGImageRef imgref = [UIImage imageFromSampleBufferRef:buffer]; //读取CMSampleBuffer中的数据，将其转化为CGImageRef 参考代码见：http://www.jianshu.com/p/3d5ccbde0de1 UIImage *img = [UIImage imageWithCGImage:imgref]; dispatch_sync(dispatch_get_main_queue(), ^{ _imageView.image = img; }); } } else { isComplete = YES; } if(isComplete) { //关闭写入会话 [_assetWrite finishWritingWithCompletionHandler:^{ AVAssetWriterStatus status = self.assetWrite.status; if (status == AVAssetWriterStatusCompleted) { NSLog(@"finsished"); } else { NSLog(@"failure"); } }]; } } }]; } }
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