使用AVFoundation给视频加水印

几个重要的Point：
1.使用AVfoundation速度快，性能好；使用GPUImage兼容性好。综合业务需求自行选择。
2.视频的剪切，拼接操作都是由insertTimeRange控制。另外此处涉及到CMTime相关知识，就不再赘述，不懂的童鞋可自行Google。

[videoTrack insertTimeRange:CMTimeRangeMake(startTime, duration) ofTrack:videoAssetTrack atTime:kCMTimeZero error:nil];

3.关于视频尺寸的裁剪（长方形视频，裁剪为正方形），由renderSize控制。

videoComposition.renderSize = CGSizeMake(renderWidth, renderHeight);

4.但是裁剪出来的正方形视频不是居中裁剪的啊，那就使用平移大法：

    // 控制裁剪居中
    videoTransform = CGAffineTransformTranslate(videoTransform, 0, -(naturalSize.height - naturalSize.width) / 2.f);

好了，废话不多说，直接上代码：

- (void)addWaterMarkByAVFoundation {
    
    NSURL *videoURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"IMG_4400" ofType:@"m4v"]];
    
    NSDictionary *options = [NSDictionary dictionaryWithObject:@(YES) forKey:AVURLAssetPreferPreciseDurationAndTimingKey];
    AVURLAsset *videoAsset = [AVURLAsset URLAssetWithURL:videoURL options:options];
    
    CMTime startTime = CMTimeMake(0, videoAsset.duration.timescale);
    CMTime duration = CMTimeMake(videoAsset.duration.value, videoAsset.duration.timescale);
    
    AVMutableComposition *mixComposition = [[AVMutableComposition alloc] init];
    
    // 视频轨道
    AVMutableCompositionTrack *videoTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    AVAssetTrack *videoAssetTrack = [videoAsset tracksWithMediaType:AVMediaTypeVideo].firstObject;
    [videoTrack insertTimeRange:CMTimeRangeMake(startTime, duration) ofTrack:videoAssetTrack atTime:kCMTimeZero error:nil];
    
    // 音频轨道
    AVMutableCompositionTrack *audioTrack = [mixComposition addMutableTrackWithMediaType:AVMediaTypeAudio preferredTrackID:kCMPersistentTrackID_Invalid];
    AVAssetTrack *audioAssetTrack = [videoAsset tracksWithMediaType:AVMediaTypeAudio].firstObject;
    [audioTrack insertTimeRange:CMTimeRangeMake(startTime, duration) ofTrack:audioAssetTrack atTime:kCMTimeZero error:nil];
    
    // 视频方向
    BOOL isVideoAssetPortrait = NO;
    CGAffineTransform videoTransform = videoAssetTrack.preferredTransform;
    if (videoTransform.a == 0 && videoTransform.b == 1.0 && videoTransform.c == -1.0 && videoTransform.d == 0) {
        isVideoAssetPortrait = YES;
    }else if (videoTransform.a == 0 && videoTransform.b == -1.0 && videoTransform.c == 1.0 && videoTransform.d == 0) {
        isVideoAssetPortrait = YES;
    }
    
    // 渲染尺寸
    CGSize naturalSize;
    if (isVideoAssetPortrait) {
        naturalSize = CGSizeMake(videoAssetTrack.naturalSize.height, videoAssetTrack.naturalSize.width);
    }else {
        naturalSize = videoAssetTrack.naturalSize;
    }
    CGFloat renderWidth = naturalSize.width;
    CGFloat renderHeight = naturalSize.width;
    
    // 裁剪居中
    videoTransform = CGAffineTransformTranslate(videoTransform, 0, -(naturalSize.height - naturalSize.width) / 2.f);
    
    AVAssetTrack *track = [mixComposition tracksWithMediaType:AVMediaTypeVideo].firstObject;
    AVMutableVideoCompositionLayerInstruction *videoLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:track];
    [videoLayerInstruction setTransform:videoTransform atTime:kCMTimeZero];
    [videoLayerInstruction setOpacity:0.0 atTime:duration];
    
    AVMutableVideoCompositionInstruction *videoInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    videoInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, duration);
    videoInstruction.layerInstructions = @[videoLayerInstruction];
    
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.renderSize = CGSizeMake(renderWidth, renderHeight);
    videoComposition.instructions = @[videoInstruction];
    videoComposition.frameDuration = CMTimeMake(1, 25);
    [self applyVideoEffectsToComposition:videoComposition size:CGSizeMake(renderWidth, renderHeight)];
    
    
    // 输出路径
    NSString *outputPath = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Movie.mp4"];
    unlink([outputPath UTF8String]);   // 删除当前该路径下的文件
    NSURL *outputURL = [NSURL fileURLWithPath:outputPath];
    
    _exporter = [[AVAssetExportSession alloc] initWithAsset:mixComposition presetName:AVAssetExportPresetHighestQuality];
    _exporter.videoComposition = videoComposition;
    _exporter.outputURL = outputURL;
    _exporter.outputFileType = AVFileTypeQuickTimeMovie;
    _exporter.shouldOptimizeForNetworkUse = YES;
    __weak typeof(self) weakSelf = self;
    [_exporter exportAsynchronouslyWithCompletionHandler:^{
        // 视频输出完成
        switch (weakSelf.exporter.status) {
            case AVAssetExportSessionStatusCompleted:
                [weakSelf saveVideoToLibrary:outputPath];
                break;
            case AVAssetExportSessionStatusFailed:
                kShowPopTip(nil, @"导出失败", nil);
                break;
            case AVAssetExportSessionStatusCancelled:
                kShowPopTip(nil, @"导出取消", nil);
                break;
            default:
                break;
        }
    }];
}

- (void)saveVideoToLibrary:(NSString *)outputPath {
    if ([PHPhotoLibrary authorizationStatus] == PHAuthorizationStatusAuthorized) {
        
        __block PHObjectPlaceholder *placeholder;
        if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(outputPath)) {
            NSError *error;
            [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
                PHAssetChangeRequest* createAssetRequest = [PHAssetChangeRequest creationRequestForAssetFromVideoAtFileURL:[NSURL URLWithString:outputPath]];
                placeholder = [createAssetRequest placeholderForCreatedAsset];
            } error:&error];
            if (error) {
                kShowPopTip(self.view, error.description, nil);
            }else {
                kShowPopTip(self.view, @"视频已保存到相册", nil);
            }
        }
    }
}

- (void)applyVideoEffectsToComposition:(AVMutableVideoComposition *)videoComposition size:(CGSize)size {
    
    NSString *text = @"@Ander";
    UIFont *font = kFontFromPx(100);
    CGFontRef fontRef = CGFontCreateWithFontName((__bridge CFStringRef)font.fontName);
    CATextLayer *textLayer = [[CATextLayer alloc] init];
    textLayer.fontSize = font.pointSize;
    textLayer.font = fontRef;
    textLayer.string = text;
    textLayer.alignmentMode = kCAAlignmentCenter;
    textLayer.foregroundColor = kColorWithRGB(0xFFFFFF).CGColor;
    textLayer.backgroundColor = [UIColor redColor].CGColor;
    CGSize textSize = [text sizeWithAttributes:[NSDictionary dictionaryWithObjectsAndKeys:font, NSFontAttributeName, nil]];
    textLayer.frame = CGRectMake(50, 100, textSize.width + 20, textSize.height + 20);
    CGFontRelease(fontRef);
    
    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];
    [parentLayer addSublayer:textLayer];
    
    videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
}