iOS|iOS 基于Metal的本地视频渲染流程及详细解析 iOS基于Metal的本地视频渲染流程

1.本地视频的渲染流程与AVFoundation采集的视频流渲染流程完全一致，只不过视频流的来源不同，一个是AVFoundation采集的CMSampleBufferRef和AVAssetReader读取本地视频文件的CMSampleBufferRef， AVFoundation这个采集的是异步的所以数据来了生成准备好的Y和UV纹理，AVAssetReader可以用的时候再读取 2. AVAssetReader 相关的本地视频文件读取类代码实现

#import @interface CCAssetReader : NSObject//初始化 - (instancetype)initWithUrl:(NSURL *)url; //从MOV文件读取CMSampleBufferRef 数据 - (CMSampleBufferRef)readBuffer;

@implementation CCAssetReader { //轨道 AVAssetReaderTrackOutput *readerVideoTrackOutput; //AVAssetReader可以从原始数据里获取解码后的音视频数据 AVAssetReader*assetReader; //视频地址 NSURL *videoUrl; //锁 NSLock *lock; }//初始化 - (instancetype)initWithUrl:(NSURL *)url{self = [super init]; if(self != nil) { videoUrl = url; lock = [[NSLock alloc]init]; [self setUpAsset]; } return self; }//Asset 相关设置 -(void)setUpAsset{//AVURLAssetPreferPreciseDurationAndTimingKey 默认为NO,YES表示提供精确的时长 NSDictionary *inputOptions = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:YES] forKey:AVURLAssetPreferPreciseDurationAndTimingKey]; //1. 创建AVURLAsset 是AVAsset 子类,用于从本地/远程URL初始化资源 AVURLAsset *inputAsset = [[AVURLAsset alloc] initWithURL:videoUrl options:inputOptions]; //2.异步加载资源 //weakSelf 解决循环引用 __weak typeof(self) weakSelf = self; //定义属性名称 NSString *tracks = @"tracks"; //对资源所需的键执行标准的异步载入操作,这样就可以访问资源的tracks属性时,就不会受到阻碍. [inputAsset loadValuesAsynchronouslyForKeys:@[tracks] completionHandler: ^{//延长self 生命周期 __strong typeof(self) strongSelf = weakSelf; //开辟子线程并发队列异步函数来处理读取的inputAsset dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ NSError *error = nil; //获取状态码. AVKeyValueStatus tracksStatus = [inputAsset statusOfValueForKey:@"tracks" error:&error]; //如果状态不等于成功加载,则返回并打印错误信息 if (tracksStatus != AVKeyValueStatusLoaded) { NSLog(@"error %@", error); return; } //处理读取的inputAsset [weakSelf processWithAsset:inputAsset]; }); }]; }//处理获取到的asset - (void)processWithAsset:(AVAsset *)asset { //锁定 [lock lock]; NSLog(@"processWithAsset"); NSError *error = nil; //1.创建AVAssetReader assetReader = [AVAssetReader assetReaderWithAsset:asset error:&error]; //2.kCVPixelBufferPixelFormatTypeKey 像素格式. /* kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange : 420v kCVPixelFormatType_32BGRA : iOS在内部进行YUV至BGRA格式转换 */ NSMutableDictionary *outputSettings = [NSMutableDictionary dictionary]; [outputSettings setObject:@(kCVPixelFormatType_420YpCbCr8BiPlanarFullRange) forKey:(id)kCVPixelBufferPixelFormatTypeKey]; /*3. 设置readerVideoTrackOutput assetReaderTrackOutputWithTrack:(AVAssetTrack *)track outputSettings:(nullable NSDictionary *)outputSettings 参数1: 表示读取资源中什么信息参数2: 视频参数 */ readerVideoTrackOutput = [AVAssetReaderTrackOutput assetReaderTrackOutputWithTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0] outputSettings:outputSettings]; //alwaysCopiesSampleData : 表示缓存区的数据输出之前是否会被复制.YES:输出总是从缓存区提供复制的数据,你可以自由的修改这些缓存区数据 readerVideoTrackOutput.alwaysCopiesSampleData = https://www.it610.com/article/NO; //4.为assetReader 填充输出 [assetReader addOutput:readerVideoTrackOutput]; //5.assetReader 开始读取.并且判断是否开始. if ([assetReader startReading] == NO) { NSLog(@"Error reading from file at URL: %@", asset); }//取消锁 [lock unlock]; }//读取Buffer 数据 - (CMSampleBufferRef)readBuffer { //锁定 [lock lock]; CMSampleBufferRef sampleBufferRef = nil; //1.判断readerVideoTrackOutput 是否创建成功. if (readerVideoTrackOutput) {//复制下一个缓存区的内容到sampleBufferRef sampleBufferRef = [readerVideoTrackOutput copyNextSampleBuffer]; }//2.判断assetReader 并且status 是已经完成读取则重新清空readerVideoTrackOutput/assetReader.并重新初始化它们 if (assetReader && assetReader.status == AVAssetReaderStatusCompleted) { NSLog(@"customInit"); readerVideoTrackOutput = nil; assetReader = nil; [self setUpAsset]; }//取消锁 [lock unlock]; //3.返回读取到的sampleBufferRef 数据 return sampleBufferRef; }

3.渲染代码的差异，直接读取CMSampleBuffer

- (void)drawInMTKView:(MTKView *)view {//1.每次渲染都要单独创建一个CommandBuffer id commandBuffer = [self.commandQueue commandBuffer]; //获取渲染描述信息 MTLRenderPassDescriptor *renderPassDescriptor = view.currentRenderPassDescriptor; //2. 从CCAssetReader中读取图像数据 CMSampleBufferRef sampleBuffer = [self.reader readBuffer]; //3.判断renderPassDescriptor 和 sampleBuffer 是否已经获取到了? if(renderPassDescriptor && sampleBuffer) { //4.设置renderPassDescriptor中颜色附着(默认背景色) renderPassDescriptor.colorAttachments[0].clearColor = MTLClearColorMake(0.0, 0.5, 0.5, 1.0f); //5.根据渲染描述信息创建渲染命令编码器 id renderEncoder = [commandBuffer renderCommandEncoderWithDescriptor:renderPassDescriptor]; //6.设置视口大小(显示区域) [renderEncoder setViewport:(MTLViewport){0.0, 0.0, self.viewportSize.x, self.viewportSize.y, -1.0, 1.0 }]; //7.为渲染编码器设置渲染管道 [renderEncoder setRenderPipelineState:self.pipelineState]; //8.设置顶点缓存区 [renderEncoder setVertexBuffer:self.vertices offset:0 atIndex:CCVertexInputIndexVertices]; //9.设置纹理(将sampleBuffer数据设置到renderEncoder 中) [self setupTextureWithEncoder:renderEncoder buffer:sampleBuffer]; //10.设置片元函数转化矩阵 [renderEncoder setFragmentBuffer:self.convertMatrix offset:0 atIndex:CCFragmentInputIndexMatrix]; //11.开始绘制 [renderEncoder drawPrimitives:MTLPrimitiveTypeTriangle vertexStart:0 vertexCount:self.numVertices]; //12.结束编码 [renderEncoder endEncoding]; //13.显示 [commandBuffer presentDrawable:view.currentDrawable]; }//14.提交命令 [commandBuffer commit]; }