一.AVFoundation基础
AVFoundation是一个可以用来使用和创建基于时间的视听媒体的框架，它提供了一个能使用基于时间的视听数据的详细级别的Objective-C接口。例如：您可以用它来检查，创建，编辑或是重新编码媒体文件。也可以从设备中获取输入流，在视频实时播放时操作和回放。
AVAsset
AVFoundation框架用来表示媒体的主要类是AVAsset。AVAsset实例的媒体数据是一个或更多个（音频和视频轨道）的集合的聚集表示。它规定将有关集合的信息作为一个整体，如它的名称，时间，自然呈现大小等的信息，AVAsset不依赖于特定的数据格式。
CMTime
typedef struct{
CMTimeValue value;
CMTimeScale timescale;
CMTimeFlags flags;
CMTimeEpoch epoch;
} CMTime;
CMTime定义是一个C语言的结构体，CMTime是以分数的形式表示时间，value表示分子，timescale表示分母，flags是位掩码，表示时间的指定状态。在AVFoundation中使用CMTime来作为操作的时间单位，使得操作粒度非常精确。
使用AVFoundation可以很方便的完成几项工作：
媒体播放：使用
player item和player item tracks，你可以设置被播放器呈现的项目中可视的那一部分，设置音频的混合参数以及被应用于播放期间的视频组合设定，或者播放期间的禁用组件。读取，写入和重新编码媒体：
AVFoundation允许你用几种方式创建新的asset的表现形式。你可以简单将已经存在的asset重新编码或者在编辑后再保存为一个新的asset。获取视频缩略图：想要生成缩略图的
asset初始化一个AVAssetImageGenerator的实例。AVAssetImageGenerator使用默认启用视频轨道来生成图像。编辑视频：
AVFoundation使用compositions去从现有的媒体片段（通常是一个或多个视频和音频轨道）创建新的assets。你可以使用一个composition去添加和删除轨道，并调整它们的时间排序。你也可以设置相对音量和增加音频轨道，并且设置不透明度，浑浊坡道，视频跟踪。相机和麦克风捕获：iOS的相机和麦克风输入由一个
capture session管理。
二.AVFoundation播放
AVPlayer用于播放多媒体的播放器，使用AVPlayerItem作为播放管理单元，我们可以通过编辑它的轨道来实现加速/禁音播放等效果，通过KVO来监听当前播放的进度和状态，当播放的时候会通过KVO渲染到AVPlayerLayer上。
// 设置监听粒度
- (void)setupCurrentCMTimeObserver {
self.observeCMTime = YES;
__weak typeof(self) weakSelf = self;
if (CMTIME_IS_INVALID(self.currentTimeObserverInterval)) {
_currentTimeObserverInterval = CMTimeMake(1, 10);
}
self.currentCMTimeObserver = [self.player addPeriodicTimeObserverForInterval:self.currentTimeObserverInterval queue:dispatch_get_main_queue() usingBlock:^(CMTime time) {
if (weakSelf.observeCMTime) {
weakSelf.currentTime = CMTimeGetSeconds(time) * weakSelf.speed;
}
}];
}
- (void)startObservePlayerItemProperties {
if (self.playerItem) {
[self.playerItem addObserver:self forKeyPath:@"duration" options:NSKeyValueObservingOptionNew context:NULL];
[self.playerItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:NULL];
[self.playerItem addObserver:self forKeyPath:@"playbackBufferEmpty" options:NSKeyValueObservingOptionNew context:NULL];
[self.playerItem addObserver:self forKeyPath:@"playbackLikelyToKeepUp" options:NSKeyValueObservingOptionNew context:NULL];
self.observingPlayerItem = YES;
}
}
- (void)stopObservePlayerItemProperties {
if (self.playerItem && self.observingPlayerItem) {
self.observingPlayerItem = NO;
[self.playerItem removeObserver:self forKeyPath:@"duration"];
[self.playerItem removeObserver:self forKeyPath:@"status"];
[self.playerItem removeObserver:self forKeyPath:@"playbackBufferEmpty"];
[self.playerItem removeObserver:self forKeyPath:@"playbackLikelyToKeepUp"];
}
}
- (void)reobserveNotifications {
if (self.observerArray.count) {
for (id observer in self.observerArray) {
[[NSNotificationCenter defaultCenter] removeObserver:observer];
}
}
self.observerArray = [NSMutableArray array];
__weak typeof(self) weakSelf = self;
{
id observer = [[NSNotificationCenter defaultCenter] addObserverForName:AVPlayerItemDidPlayToEndTimeNotification object:self.playerItem queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification * _Nonnull note) {
weakSelf.didStart = NO;
weakSelf.isFinish = YES;
if (weakSelf.delegate && [weakSelf.delegate respondsToSelector:@selector(videoPlayerDidFinish:)]) {
[weakSelf.delegate videoPlayerDidFinish:weakSelf];
}
[weakSelf stopUpdateStatisticTimer];
}];
[self.observerArray addObject:observer];
}
{
id observer = [[NSNotificationCenter defaultCenter] addObserverForName:AVPlayerItemFailedToPlayToEndTimeNotification object:self.playerItem queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification * _Nonnull note) {
NSError *error = [note.userInfo objectForKey:AVPlayerItemFailedToPlayToEndTimeErrorKey];
[weakSelf handlePlayFailWithError:error];
}];
[self.observerArray addObject:observer];
}
{
id observer = [[NSNotificationCenter defaultCenter] addObserverForName:AVPlayerItemNewErrorLogEntryNotification object:self.playerItem queue:[NSOperationQueue mainQueue] usingBlock:^(NSNotification * _Nonnull note) {
AVPlayerItem *item = note.object;
AVPlayerItemErrorLog *errorLog = item.errorLog;
if (errorLog.events.count) {
AVPlayerItemErrorLogEvent *event = errorLog.events.lastObject;
NSError *error = [NSError errorWithDomain:event.errorDomain code:event.errorStatusCode userInfo:@{@"errorLogEvent": event}];
[weakSelf handlePlayFailWithError:error];
}
}];
[self.observerArray addObject:observer];
}
}
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {
if (object == self.playerItem) {
if ([keyPath isEqualToString:@"duration"]) {
if (self.delegate && [self.delegate respondsToSelector:@selector(videoPlayer:didUpdateDuration:)]) {
[self.delegate videoPlayer:self didUpdateDuration:CMTimeGetSeconds(self.playerItem.duration)];
}
} else if ([keyPath isEqualToString:@"playbackBufferEmpty"]) {
} else if ([keyPath isEqualToString:@"playbackLikelyToKeepUp"]) {
NSLog(@"observeValueForKeyPath: playbackLikelyToKeepUp = %d", self.playerItem.playbackLikelyToKeepUp);
if (self.delegate && [self.delegate respondsToSelector:@selector(videoPlayer:bufferToBeKeepUp:)]) {
[self.delegate videoPlayer:self bufferToBeKeepUp:self.playerItem.playbackLikelyToKeepUp];
}
} else if ([keyPath isEqualToString:@"status"]) {
if (self.playerItem.status == AVPlayerItemStatusFailed) {
[self handlePlayFailWithError:self.playerItem.error];
} else if (self.playerItem.status == AVPlayerItemStatusReadyToPlay) {
}
}
} else if (object == self.playerLayer) {
if (self.playerLayer.readyForDisplay) {
self.didGetFirstFrame = YES;
}
} else if (object == self.player) {
if (self.player.status == AVPlayerStatusFailed) {
[self handlePlayFailWithError:self.player.error];
}
}
}
- (AVPlayerItem *)playerItemWithAsset:(AVAsset *)asset
{
AVPlayerItem *playerItem = nil;
if (self.speed == 1) {
playerItem = [AVPlayerItem playerItemWithAsset:asset];
} else {
CMTime duration = asset.duration;
AVMutableComposition *composition = [AVMutableComposition composition];
[composition insertTimeRange:CMTimeRangeMake(kCMTimeZero, duration) ofAsset:asset atTime:kCMTimeZero error:nil];
if (self.speed != 0) {
[composition scaleTimeRange:CMTimeRangeMake(kCMTimeZero, duration) toDuration:CMTimeMultiplyByFloat64(duration, 1 / self.speed)];
}
playerItem = [AVPlayerItem playerItemWithAsset:composition];
if ([composition tracksWithMediaType:AVMediaTypeVideo].count && [asset tracksWithMediaType:AVMediaTypeVideo].count) {
AVMutableCompositionTrack *track = [composition tracksWithMediaType:AVMediaTypeVideo][0];
track.preferredTransform = [asset tracksWithMediaType:AVMediaTypeVideo][0].preferredTransform;
}
}
return playerItem;
}
//初始化并开始播放
- (void)initPlayerWithPlayItem:(AVPlayerItem *)playItem
{
self.currentTimeObserverInterval = CMTimeMake(1, 10);
self.playerItem = playItem;
[self startObservePlayerItemProperties];
self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
[self.player addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:NULL];
self.player.muted = self.shouldMute;
self.playerLayer = [AVPlayerLayer playerLayerWithPlayer:self.player];
self.playerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
[self.playerLayer addObserver:self forKeyPath:@"readyForDisplay" options:NSKeyValueObservingOptionNew context:NULL];
[self reobserveNotifications];
[self setupCurrentCMTimeObserver];
[self.player play];
}
三.AVFoundation重新编码
AVAssetReader：用于从AVAssert实例中读取媒体样本。
每个
AVAssetReader对象在某个时刻只能和单个asset关联，但这个asset可包含多个tracks。所以，在开始读取之前，必须给asset reader指定一个AVAssetReaderOutput的具体子类，来配置media data怎样读取。可通过
copyNextSampleBuffer方法可以访问音频样本和视频帧。
AVAssetWriter：将媒体数据从多个源写入指定文件格式的单个文件。
不需要将
asset writer对象与特定的asset相关联，但必须为要创建的每个输出文件使用单独的asset writer。由于
asset writer可以从多个源写入媒体数据，因此必须要为写入文件的每个track创建一个AVAssetWriterInput对象，每个AVAssetWriterInput期望以CMSampleBufferRef对象形式接收数据，但如果你想要将CVPixelBufferRef类型对象添加到asset writer input，就使用AVAssetWriterInputPixelBufferAdaptor类。
- (void)initReader
{
self.reader = [[AVAssetReader alloc]initWithAsset:self.inputAsset error:nil];
NSArray *videoTracks = [self.inputAsset tracksWithMediaType:AVMediaTypeVideo];
NSDictionary *decompressionVideoSettings = @{
(id)kCVPixelBufferPixelFormatTypeKey : [NSNumber numberWithUnsignedInt:kCVPixelFormatType_32ARGB],
(id)kCVPixelBufferIOSurfacePropertiesKey : [NSDictionary dictionary]
};
self.videoCompositionOutput = [AVAssetReaderVideoCompositionOutput assetReaderVideoCompositionOutputWithVideoTracks:videoTracks
videoSettings:decompressionVideoSettings];
self.videoComposition = [AVVideoComposition videoCompositionWithPropertiesOfAsset:self.inputAsset];
self.videoComposition = [AVVideoComposition videoCompositionWithPropertiesOfAsset:self.inputAsset];
self.videoCompositionOutput.videoComposition = self.videoComposition;
if ([self.reader canAddOutput:self.videoCompositionOutput]){
[self.reader addOutput:self.videoCompositionOutput];
}
[self.reader startReading];
}
- (void)initWriter
{
NSURL *outputFileURL = [FRVideoEditExportCache storyClockOutputUrl];
self.writer = [AVAssetWriter assetWriterWithURL:outputFileURL
fileType:AVFileTypeMPEG4
error:nil];
NSDictionary *videoCompressionSettings = [NSDictionary dictionaryWithObjectsAndKeys:
AVVideoCodecH264, AVVideoCodecKey,
[NSNumber numberWithInteger:self.videoComposition.renderSize.width], AVVideoWidthKey,
[NSNumber numberWithInteger:self.videoComposition.renderSize.height], AVVideoHeightKey,
nil];
self.writerVideoInput = [AVAssetWriterInput assetWriterInputWithMediaType:AVMediaTypeVideo outputSettings:videoCompressionSettings];
self.writerVideoInput.expectsMediaDataInRealTime = YES;
NSDictionary *sourceBufferAttribute = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInteger:kCVPixelFormatType_32ARGB], (id)kCVPixelBufferPixelFormatTypeKey,
[NSNumber numberWithUnsignedInteger:self.videoComposition.renderSize.width], (id)kCVPixelBufferWidthKey,
[NSNumber numberWithUnsignedInteger:self.videoComposition.renderSize.height], (id)kCVPixelBufferHeightKey,
(id)kCFBooleanTrue, (id)kCVPixelFormatOpenGLESCompatibility,
nil];
self.writerInputPixelBufferAdaptor = [AVAssetWriterInputPixelBufferAdaptor assetWriterInputPixelBufferAdaptorWithAssetWriterInput:self.writerVideoInput
sourcePixelBufferAttributes:sourceBufferAttribute];
if([self.writer canAddInput:self.writerVideoInput]){
[self.writer addInput:self.writerVideoInput];
}
[self.writer startWriting];
}
- (void)readWrite:(AVAsset *)asset
{
self.inputAsset = asset;
__weak typeof(self)weakSelf = self;
dispatch_async(self.queue, ^{
[weakSelf initReader];
[weakSelf initWriter];
// 从reader中拷贝出元视频数据
CMSampleBufferRef buffer = [weakSelf.videoCompositionOutput copyNextSampleBuffer];
while (buffer != NULL) {
CMItemCount count = CMSampleBufferGetNumSamples(buffer);
if (!count) {
break;
}
// 获取元数据及其信息
CMTime presentationTime = CMSampleBufferGetOutputPresentationTimeStamp(buffer);
CVPixelBufferRef pixelBuffer = CMSampleBufferGetImageBuffer(buffer);
// 写回到Writer中
if (!weakSelf.videoWritingStarted){
weakSelf.videoWritingStarted = YES;
[weakSelf.writer startSessionAtSourceTime:presentationTime];
}
if (weakSelf.writerVideoInput.readyForMoreMediaData){
[weakSelf.writerInputPixelBufferAdaptor appendPixelBuffer:pixelBuffer withPresentationTime:presentationTime];
}
CFRelease(buffer);
buffer = NULL;
buffer = [weakSelf.videoCompositionOutput copyNextSampleBuffer];
}
[weakSelf.writer finishWritingWithCompletionHandler:^(void){
weakSelf.videoWritingStarted = NO;
switch (weakSelf.writer.status) {
case AVAssetWriterStatusFailed:{
NSLog(@"Write fail");
break;
}
case AVAssetWriterStatusCompleted:{
NSLog(@"Write compelte");
break;
}
default:
break;
}
}];
});
}
四.AVFoundation获取缩略图
AVAssetImageGenerator：用于获取视频的缩略图，它可以异步获取到一组采样点（CMTime）的缩略图，精确的采样点为视频压缩时的presentationTime。
- (void)setUrl:(NSURL *)url
{
_url = url;
_asset = nil;
_imageGenerator = nil;
}
- (AVAsset *)asset
{
if(_asset == nil && _url){
_asset = [AVAsset assetWithURL:_url];
}
return _asset;
}
- (AVAssetImageGenerator *)imageGenerator
{
if(!_url){
_imageGenerator = nil;
}
if(_imageGenerator == nil && self.asset){
_imageGenerator = [[AVAssetImageGenerator alloc]initWithAsset:_asset];
_imageGenerator.maximumSize = CGSizeMake(self.imageSize.width * [UIScreen mainScreen].scale, self.imageSize.height * [UIScreen mainScreen].scale);
_imageGenerator.appliesPreferredTrackTransform = YES;
_imageGenerator.requestedTimeToleranceBefore = kCMTimeZero;
_imageGenerator.requestedTimeToleranceAfter = kCMTimeZero;
}
return _imageGenerator;
}
- (void)generateUnscaledCGImagesAsynchronouslyForTimes:(NSArray<NSValue *> *)requestedTimes completionHandler:(AVAssetImageGeneratorCompletionHandler)handler {
if (!self.imageGenerator) {
return;
}
self.imageGenerator.maximumSize = CGSizeZero;
[self.imageGenerator generateCGImagesAsynchronouslyForTimes:requestedTimes completionHandler:handler];
self.imageGenerator.maximumSize = CGSizeMake(self.imageSize.width * [UIScreen mainScreen].scale, self.imageSize.height * [UIScreen mainScreen].scale);
}
五.AVFoundation视频编辑
我们使用MediaComposition 来进行视频编辑，其中文档中将相关类分为几个部分来介绍：
- Media Composition：用于表示多条媒体轨道合集以及在合集层级操作相关的类。包括AVComposition，AVMutableComposition，AVCompositionTrack，AVMutableCompositionTrack，AVCompositionTrackSegment。
- Video Composition：表示视频轨道处理相关类。
- Movie Editing：QuikTime视频处理相关类。
- Audio Mixing：音频合成处理相关类。
实例可参考官方Demo：AVSimpleEditoriOS
添加水印/设置遮罩
- (CALayer *)parentLayer
{
if(!_parentLayer){
_parentLayer = [CALayer layer];
_parentLayer.backgroundColor = [UIColor whiteColor].CGColor;
}
return _parentLayer;
}
- (CALayer *)videoLayer
{
if(!_videoLayer){
_videoLayer = [CALayer layer];
}
return _videoLayer;
}
- (AVMutableVideoComposition *)maskWithInputAsset:(AVAsset *)asset
{
// 初始化Composition
if(!self.mutableComposition){
self.mutableComposition = [AVMutableComposition composition];
AVAssetTrack *assetVideoTrack = nil;
AVAssetTrack *assetAudioTrack = nil;
if ([[asset tracksWithMediaType:AVMediaTypeVideo] count] != 0) {
assetVideoTrack = [asset tracksWithMediaType:AVMediaTypeVideo][0];
}
if ([[asset tracksWithMediaType:AVMediaTypeAudio] count] != 0) {
assetAudioTrack = [asset tracksWithMediaType:AVMediaTypeAudio][0];
}
CMTime duration = [asset duration];
if(assetVideoTrack != nil) {
AVMutableCompositionTrack *compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, duration) ofTrack:assetVideoTrack atTime:kCMTimeZero error:nil];
compositionVideoTrack.preferredTransform = assetVideoTrack.preferredTransform;
}
if(assetAudioTrack != nil) {
AVMutableCompositionTrack *compositionAudioTrack = [composition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[compositionAudioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, duration) ofTrack:assetAudioTrack atTime:kCMTimeZero error:nil];
}
}
// 初始化VideoComposition
if (!self.mutableVideoComposition) {
//初始化容器大小和间隔
AVAssetTrack *videoTrack = [self.mutableComposition tracksWithMediaType:AVMediaTypeVideo][0];
self.mutableVideoComposition = [AVMutableVideoComposition videoComposition];
self.mutableVideoComposition.frameDuration = CMTimeMake(1, videoTrack.nominalFrameRate + 10);//渲染帧数太少会直接导致质量下降
self.mutableVideoComposition.renderSize = videoTrack.naturalSize;
self.mutableVideoComposition.renderScale = 1.0;
//指定添加layer指令
self.instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
self.instruction.timeRange = CMTimeRangeMake(kCMTimeZero, [self.mutableComposition duration]);
self.layerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
self.instruction.layerInstructions = @[self.layerInstruction];
self.mutableVideoComposition.instructions = @[self.instruction];
}
// 水印/遮罩都可以通过设置videoLayer来实现
CGSize renderSize = self.mutableVideoComposition.renderSize;
CGFloat maskLength = renderSize.width > renderSize.height ? renderSize.height : renderSize.width;
CGFloat maskOffset = ABS(renderSize.width - renderSize.height);
CGSize maskSize = CGSizeMake(maskLength, maskLength);
CGRect maskFrame = CGRectMake(0, 0, maskSize.width, maskSize.height);
CAShapeLayer *maskLayer = [CAShapeLayer layer];
CGFloat radius = maskSize.width /2.0;
UIBezierPath *circlePath = [UIBezierPath bezierPathWithArcCenter:CGPointMake(maskSize.width/2, maskSize.height/2)
radius:radius
startAngle:0
endAngle:2 * M_PI
clockwise:NO];
maskLayer.path = circlePath.CGPath;
// 当起始点变化的时候，Composition也需要进行移动
CGAffineTransform transform = CGAffineTransformMakeTranslation(- maskOffset / 2.0, 0);
if(renderSize.width > renderSize.height){
transform = CGAffineTransformMakeTranslation(- maskOffset / 2.0, 0);
}else{
transform = CGAffineTransformMakeTranslation(0, - maskOffset / 2.0);
}
[self.layerInstruction setTransform:transform atTime:kCMTimeZero];
self.mutableVideoComposition.renderSize = maskSize;
// 将遮罩层添加到VideoLayer上
self.videoLayer.frame = maskFrame;
self.parentLayer.frame = maskFrame;
self.videoLayer.mask = maskLayer;
[self.parentLayer insertSublayer:self.videoLayer atIndex:0];
self.mutableVideoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:self.videoLayer inLayer:self.parentLayer];
return self.mutableVideoComposition;
}
添加音乐
// 替换音乐
+ (AVMutableComposition *)compositionWithInputAsset:(AVMutableComposition *)inputComposition audioAsset:(AVAsset *)audioAsset
{
//移除旧音频
AVAssetTrack *videoTrack = [inputComposition tracksWithMediaType:AVMediaTypeVideo][0];
[self removeAudioTrack:inputComposition];
if (!audioAsset) {
return inputComposition;
}
//添加新音频
AVMutableCompositionTrack *compositionAudioTrack = [inputComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *err = nil;
CMTime audioDuration = [audioAsset duration];
CMTime videoDuration = [videoTrack.asset duration];
err = [self resizeCompositionTrack:(AVMutableCompositionTrack *)[audioAsset tracksWithMediaType:AVMediaTypeAudio][0]
fromDuration:audioDuration
toCompositionTrack:compositionAudioTrack
toDuration:videoDuration];
if (err) {
NSLog(@"AVMutableCompositionTrack inserAudio error = %@",err);
}
return inputComposition;
}
// 添加背景音
+ (AVMutableAudioMix *)audioMixWithInputAsset:(AVMutableComposition *)inputComposition audioAsset:(AVAsset *)audioAsset
{
AVMutableAudioMix *audioMix = [AVMutableAudioMix audioMix];
AVAssetTrack *videoTrack = [inputComposition tracksWithMediaType:AVMediaTypeVideo][0];
//添加新音频
AVMutableCompositionTrack *compositionAudioTrack = [inputComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
NSError *err = nil;
CMTime audioDuration = [audioAsset duration];
CMTime videoDuration = [videoTrack.asset duration];
err = [self resizeCompositionTrack:(AVMutableCompositionTrack *)[audioAsset tracksWithMediaType:AVMediaTypeAudio][0]
fromDuration:audioDuration
toCompositionTrack:compositionAudioTrack
toDuration:videoDuration];
AVMutableAudioMixInputParameters *inputParameters = [AVMutableAudioMixInputParameters audioMixInputParametersWithTrack:compositionAudioTrack];
audioMix.inputParameters = @[inputParameters];
return audioMix;
}