效果图：
正常.gif
慢放.gif
快放.gif
倒放.gif
视频预览播放
倒入框架#import
使用AVPlayer播放视频、rate属性进行加速、减速
使用AVPlayerItem中的方法判断加速、减速
canPlaySlowReverse：支持到放
canPlaySlowForward：支持慢放
canPlayFastForward：支持快放
核心代码：
注意：倒放需要seek到视频结尾。
- (void)clickAction:(UIButton*)sender{
[self.avplayer seekToTime:kCMTimeZero];
[self.avplayer play];
switch (sender.tag) {
case 0:
if ([self.avplayer.currentItem canPlaySlowReverse]) {
self.avplayer.rate = -1.0;
[self.avplayer seekToTime:self.avplayer.currentItem.duration];
}else{
[self showAlert:@"不支持倒叙播放"];
}
break;
case 1:
self.avplayer.rate = 1;
break;
case 2:
if ([self.avplayer.currentItem canPlaySlowForward]) {
self.avplayer.rate = 0.5;
}else{
[self showAlert:@"不支持0.5倍速播放"];
}
break;
case 3:
if ([self.avplayer.currentItem canPlayFastForward]) {
self.avplayer.rate = 2.0;
}else{
[self showAlert:@"不支持2倍速播放"];
}
break;
default:
break;
}
}
生成资源视频
如果对视频资源做速度处理，我思考的原理：AVAssetReader+AVAssetWriter
倒放：我本来是想着用AVAssetWriter从后往前写入CMSampleBufferRef，苹果应该是不支持这种方式，必须要从0点开始写入。
所以需要使用resetForReadingTimeRanges方法，这个方法能够加载一个时间节点数组，倒序便利，copyNextSampleBuffer，就能取出后->前CMSampleBufferRef时间点。
使用resetForReadingTimeRanges，必须设置AVAssetReaderTrackOutput的supportsRandomAccess为YES：不按照顺序读取
获取到时间点数组、时间节点范围数组
- (void)setclipTimeRangeArray{
CMSampleBufferRef sample;
CMTime presentationTime = kCMTimeZero;
CMTime startTime = kCMTimeZero;
CMTime endTime = kCMTimeZero;
NSUInteger processIndex = 0;
self.clipTimeRangeArray = [NSMutableArray array];
self.sampleTimeArray = [NSMutableArray array];
//每10片确定一个帧组范围
while((sample = [self nextVideoSample])) {
//时间点
presentationTime = CMSampleBufferGetPresentationTimeStamp(sample);
NSValue *presentationValue = [NSValue valueWithBytes:&presentationTime objCType:@encode(CMTime)];
[self.sampleTimeArray addObject:presentationValue];
CFRelease(sample);
sample = NULL;
if (processIndex == 0) {
// startTime = presentationTime;
processIndex ++;
} else if (processIndex == 9) {
endTime = presentationTime;
CMTimeRange timeRange = CMTimeRangeMake(startTime, CMTimeSubtract(endTime, startTime));
NSValue *timeRangeValue = [NSValue valueWithCMTimeRange:timeRange];
[self.clipTimeRangeArray addObject:timeRangeValue];
processIndex = 0;
startTime = presentationTime;
endTime = kCMTimeZero;
} else {
processIndex ++;
}
}
//处理不够kClipMaxContainCount数量的帧的timerange
if (CMTIME_COMPARE_INLINE(kCMTimeZero, !=, startTime) && CMTIME_COMPARE_INLINE(kCMTimeZero, ==, endTime)) {
endTime = presentationTime;
//单独处理最后只剩一帧的情况
if (CMTIME_COMPARE_INLINE(endTime, ==, startTime) &&
processIndex == 1) {
startTime = CMTimeSubtract(startTime, CMTimeMake(1, self.videoAsset.tracks[0].nominalFrameRate));
}
CMTimeRange timeRange = CMTimeRangeMake(startTime, CMTimeSubtract(endTime, startTime));
NSValue *timeRangeValue = [NSValue valueWithCMTimeRange:timeRange];
[self.clipTimeRangeArray addObject:timeRangeValue];
}
}
针对每一个时间节点范围，获取CMSampleBufferRef，再依据元素位置获取时间点。
CMSampleBufferRef：前->后
pts：后->前
//倒序读取
- (void)nextReverseVideoSample:(void(^)(CMSampleBufferRef buffer,CMTime pts_reverse))block{
__block NSInteger index = 0;
__block NSMutableArray* bufferCaches = [NSMutableArray array];
__block NSMutableArray* ptsCaches = [NSMutableArray array];
[self.clipTimeRangeArray enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
CMSampleBufferRef buffer;
[_readerTrackOutput_video resetForReadingTimeRanges:@[obj]];
while ((buffer = [self nextVideoSample])) {
[bufferCaches addObject:(__bridge id _Nonnull)(buffer)];
[ptsCaches addObject:self.sampleTimeArray[index]];
index++;
}
[bufferCaches enumerateObjectsWithOptions:NSEnumerationReverse usingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
CMTime pts = ptsCaches[ptsCaches.count - idx - 1].CMTimeValue;
NSLog(@"==%f",CMTimeGetSeconds(pts));
block((__bridge CMSampleBufferRef)(obj),pts);
}];
[bufferCaches removeAllObjects];
[ptsCaches removeAllObjects];
}];
}
插入视频
// 开始写入
- (void)pushVideoBuffer:(CVPixelBufferRef)buffer pts:(CMTime)pts{
[NSThread sleepForTimeInterval:0.005];
if (self.assetWriterInput_video.readyForMoreMediaData) {
NSLog(@"插入图片:%f",CMTimeGetSeconds(pts));
if (buffer) {
[_adaptor appendPixelBuffer:buffer withPresentationTime:pts];
CFRelease(buffer);
buffer = NULL;
}
}else{
NSLog(@"！！！！！无法插入图片:%f---%ld",CMTimeGetSeconds(pts),(long)self.writer.status);
}
}
慢速、快速
对视频实现快速、慢速，无非是改变帧的时间点。
慢速：延长帧时间点
快放：缩小帧时间点
- (void)nextSpeedChangeFromValue:(float)slowValue VideoSample:(void(^)(CMSampleBufferRef buffer,CMTime pts_reverse))block{
__block NSInteger index = 0;
__block NSMutableArray* bufferCaches = [NSMutableArray array];
__block NSMutableArray* ptsCaches = [NSMutableArray array];
[self.clipTimeRangeArray enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
CMSampleBufferRef buffer;
[_readerTrackOutput_video resetForReadingTimeRanges:@[obj]];
while ((buffer = [self nextVideoSample])) {
[bufferCaches addObject:(__bridge id _Nonnull)(buffer)];
[ptsCaches addObject:self.sampleTimeArray[index]];
index++;
}
[bufferCaches enumerateObjectsUsingBlock:^(id _Nonnull obj, NSUInteger idx, BOOL * _Nonnull stop) {
CMTime pts = ptsCaches[idx].CMTimeValue;
pts = CMTimeMultiplyByFloat64(pts, 1/slowValue);
block((__bridge CMSampleBufferRef)(obj),pts);
}];
[bufferCaches removeAllObjects];
[ptsCaches removeAllObjects];
}];
}
GitHub：
https://github.com/qw9685/rateVideo