版权声明：原创文章，未经博主允许禁止转载。欢迎点击头像上方“郭晓东的专栏”查看专栏 https://blog.csdn.net/hherima/article/details/72725395
现手机里有一段视频，通过APP给他添加一个水印。iOS提供了在视频上添加layer的接口，添加一个水印还是很方便的(添加水印)。添加完水印有一个渲染过程，在手机这种设备上还是比较慢的，比如：对1分钟的高清视频(960x540)进行渲染需要20秒左右。如何在现有API基础上提高渲染速度，提升用户体验，成了问题。笔者发现两种渲染方法：
先看图，这有一个6秒的视频，我抓了四张关键帧。只在第2，3两张关键帧上添加字幕（一个关键帧代表1.5秒。所以，两个关键帧就代表是3秒时长）
第一种方案：视频分割 + 逐段渲染 + 合并
将视频分割为3端，即第1、第2，3、第4。有水印的是一组，没水印也是一组。对第2，3渲染。最后将三段视频合并到一起。
第二种方案：整体渲染
水印虽然不是从一开始出现，但是，我们可以对layer添加动画（参考下面OC代码）。
举个例子，假如水印少的情况。比如只对第一帧添加水印。分割渲染方案是3.0秒，整体渲染方案是3.5秒。假如水印多的情况，第1，2，3帧都有水印。分割渲染方案是4.1秒，整体渲染方案还是3.5秒。通过结果得出一点结论：整体渲染，无论水印多还是少，耗时是一样的。分割渲染怎么会有这么个差别呢？
分割渲染：由于涉及三步：1.分割，2.渲染视频，3.合并视频。每一步都需要时间。根据测试经验，第一步分割视频的时间很少，可以忽略。那么就剩下渲染和合并时间了。就拿刚才6秒的视频来说：一张水印和三张水印。合并视频时间是一样的。都是两段（一段1.5秒，另外一段4.5秒）。但是水印多了渲染时间就长了。
最后得出结论：水印少的时候，使用分割渲染方法。水印多的情况使用整体渲染。
整体渲染代码：
#define kEffectVideoFileName_Animation @"tmpMov-effect.mov"
- (void)renderWholeVideo:(AVAsset *)asset{
// 1 - Early exit if there's no video file selected
if (!asset) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Error" message:@"Please Load a Video Asset First"
delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
[alert show];
return;
}
// 2 - Create AVMutableComposition object. This object will hold your AVMutableCompositionTrack instances.
AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];
// 3 - Video track
AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo
preferredTrackID:kCMPersistentTrackID_Invalid];
[videoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration)
ofTrack:[[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0]
atTime:kCMTimeZero error:nil];
AVMutableCompositionTrack *audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
[audioTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:[asset tracksWithMediaType:AVMediaTypeAudio][0] atTime:kCMTimeZero error:nil];
// 3.1 - Create AVMutableVideoCompositionInstruction
AVMutableVideoCompositionInstruction *mainInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
mainInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
// 3.2 - Create an AVMutableVideoCompositionLayerInstruction for the video track and fix the orientation.
__block CGSize naturalSize;
AVMutableVideoCompositionLayerInstruction *videolayerInstruction = [self transformVideo:asset track:videoTrack isVideoAssetPortrait:^(CGSize finalSize) {
naturalSize = finalSize;
}];
[videolayerInstruction setOpacity:0.0 atTime:asset.duration];
// 3.3 - Add instructions
mainInstruction.layerInstructions = [NSArray arrayWithObjects:videolayerInstruction,nil];
AVMutableVideoComposition *mainCompositionInst = [AVMutableVideoComposition videoComposition];
float renderWidth, renderHeight;
renderWidth = naturalSize.width;
renderHeight = naturalSize.height;
mainCompositionInst.renderSize = CGSizeMake(renderWidth, renderHeight);
mainCompositionInst.instructions = [NSArray arrayWithObject:mainInstruction];
mainCompositionInst.frameDuration = CMTimeMake(1, 30);
[self applyVideoEffectsWithAnimation:mainCompositionInst size:naturalSize];
NSString *myPathDocs = [NSTemporaryDirectory() stringByAppendingPathComponent:kEffectVideoFileName_Animation];
NSURL *url = [NSURL fileURLWithPath:myPathDocs];
/*先移除旧文件*/
[PublicUIMethod removeFile:url];
// 5 - Create exporter
AVAssetExportSession *exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition
presetName:AVAssetExportPresetHighestQuality];
[self.exportSessions addObject:exporter];
exporter.outputURL=url;
exporter.outputFileType = AVFileTypeQuickTimeMovie;
exporter.shouldOptimizeForNetworkUse = YES;
exporter.videoComposition = mainCompositionInst;
weakifyself;
[exporter exportAsynchronouslyWithCompletionHandler:^{
strongifyself;
dispatch_async(dispatch_get_main_queue(), ^{
switch ([exporter status]) {
case AVAssetExportSessionStatusFailed:
DDLogWarn(@"render Export failed: %@ and order : %d", [exporter error], 0);
break;
case AVAssetExportSessionStatusCancelled:
NSLog(@"render Export canceled order : %d", 0);
break;
default:
{
NSLog(@"'%@' render finish",[myPathDocs lastPathComponent]);
[self pushToPreviePage:myPathDocs];
}
break;
}
});
}];
[self monitorSingleExporter:exporter];
}
- (void)applyVideoEffectsWithAnimation:(AVMutableVideoComposition *)composition size:(CGSize)size
{
// Set up layer
CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, size.width, size.height);
videoLayer.frame = CGRectMake(0, 0, size.width, size.height);
[parentLayer addSublayer:videoLayer];
/**/
CMTime timeFrame = [self frameTime];
CGFloat granularity = CMTimeGetSeconds(timeFrame);
/*caption layer*/
for (int j=0; j<self.effectsArray.count; j++) {
NSArray* effectSeries = (NSArray *)self.effectsArray[j];
FSVideoCaptionDescriptionModel *description = [[effectSeries firstObject] as:FSVideoCaptionDescriptionModel.class];
NSArray *captions = [description reOrder];
if (!captions || captions.count == 0) {
//没有字幕就别瞎搞了
continue;
}
FSCaptionModel *captionModel = captions.firstObject;
UIImage *image = captionModel.image;/*将水印生成图片，采用图片方法添加水印*/
CGFloat scaleY = captionModel.scaleY;
CGFloat scaleHeight = captionModel.scaleHeight;
CALayer *layer = [CALayer layer];
layer.frame = CGRectMake(0, size.height * scaleY, size.width, size.height * scaleHeight);
layer.contents = (__bridge id)image.CGImage;
/*
字幕动画由两个组成:
1. 显示所有字幕<动画开始前保持，初始状态。动画时间是0.结束后不移除动画>
2. 隐藏字幕，到最后。
*/
CGFloat showStartTime = description.startIndex * granularity;
CGFloat hiddenAginStartTime = showStartTime + effectSeries.count*granularity;
CABasicAnimation *animation = nil;
if (showStartTime > 0) {
animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault];
[animation setFromValue:[NSNumber numberWithFloat:0.0]];
[animation setToValue:[NSNumber numberWithFloat:1.0]];
[animation setBeginTime:showStartTime];
[animation setFillMode:kCAFillModeBackwards];/*must be backwards*/
[animation setRemovedOnCompletion:NO];/*must be no*/
[layer addAnimation:animation forKey:@"animateOpacityShow"];
}
/*最后一个字幕片段不是整的1.5s或者5秒。就不隐藏动画了*/
if (j != self.effectsArray.count-1) {
animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
animation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionDefault];
[animation setFromValue:[NSNumber numberWithFloat:1.0]];
[animation setToValue:[NSNumber numberWithFloat:0.0]];
[animation setBeginTime:hiddenAginStartTime];
[animation setRemovedOnCompletion:NO];/*must be no*/
[animation setFillMode:kCAFillModeForwards];
[layer addAnimation:animation forKey:@"animateOpacityHiddenAgin"];
}
[parentLayer addSublayer:layer];
}
parentLayer.geometryFlipped = YES;
composition.animationTool = [AVVideoCompositionCoreAnimationTool
videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
}
- (void)monitorSingleExporter:(AVAssetExportSession *)exporter{
double delay = 1.0;
int64_t delta = (int64_t)delay * NSEC_PER_SEC;
dispatch_time_t poptime = dispatch_time(DISPATCH_TIME_NOW, delta);
dispatch_after(poptime, dispatch_get_main_queue(), ^{
if (exporter.status == AVAssetExportSessionStatusExporting) {
NSLog(@"whole progress is %f", exporter.progress);
[self monitorSingleExporter:exporter];
}
});
}
-(AVMutableVideoCompositionLayerInstruction *) transformVideo:(AVAsset *)asset track:(AVMutableCompositionTrack *)firstTrack isVideoAssetPortrait:(void(^)(CGSize size))block{
AVMutableVideoCompositionLayerInstruction *videolayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:firstTrack];
AVAssetTrack *videoAssetTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
UIImageOrientation videoAssetOrientation_ = UIImageOrientationUp;
BOOL isVideoAssetPortrait_ = NO;
CGAffineTransform videoTransform = videoAssetTrack.preferredTransform;
if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
videoAssetOrientation_ = UIImageOrientationRight;
videoTransform = CGAffineTransformMakeRotation(M_PI_2);
videoTransform = CGAffineTransformTranslate(videoTransform, 0, -videoAssetTrack.naturalSize.height);
isVideoAssetPortrait_ = YES;
}
if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
videoAssetOrientation_ = UIImageOrientationLeft;
//这个地方很恶心，涉及到reveal看不到的坐标系
videoTransform = CGAffineTransformMakeRotation(-M_PI_2);
videoTransform = CGAffineTransformTranslate(videoTransform, - videoAssetTrack.naturalSize.width, 0);
isVideoAssetPortrait_ = YES;
}
if (videoTransform.a == 1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == 1.0) {
videoAssetOrientation_ = UIImageOrientationUp;
}
if (videoTransform.a == -1.0 && videoTransform.b == 0 && videoTransform.c == 0 && videoTransform.d == -1.0) {
videoTransform = CGAffineTransformMakeRotation(-M_PI);
videoTransform = CGAffineTransformTranslate(videoTransform, -videoAssetTrack.naturalSize.width, -videoAssetTrack.naturalSize.height);
// videoTransform = CGAffineTransformRotate(videoTransform, M_PI/180*45);
videoAssetOrientation_ = UIImageOrientationDown;
}
[videolayerInstruction setTransform:videoTransform atTime:kCMTimeZero];
CGSize naturalSize;
if(isVideoAssetPortrait_){
naturalSize = CGSizeMake(videoAssetTrack.naturalSize.height, videoAssetTrack.naturalSize.width);
} else {
naturalSize = videoAssetTrack.naturalSize;
}
if(block){
block(naturalSize);
}
return videolayerInstruction;
}