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 <AVFoundation/AVFoundation.h>
@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<NSString *, id> *)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 = 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<MTLCommandBuffer> 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<MTLRenderCommandEncoder> 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];
}
