05-11 01:40 阅读 282

[算法]iOS 视频添加水印，合成视频两种方案（整体渲染和分割渲染）

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;

}

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原文链接：https://blog.csdn.net/hherima/article/details/72725395