- (void)addWaterMark {
    /* 使用GUPImage添加水印铣卡，原理上相當于添加一層濾鏡  */
    
    NSURL *videoURL = [NSURL fileURLWithPath:[[NSBundle mainBundle] pathForResource:@"IMG_4400" ofType:@"m4v"]];
    _movieFile = [[GPUImageMovie alloc] initWithURL:videoURL];
//    _movieFile.runBenchmark = YES;
    _movieFile.playAtActualSpeed = NO;

    // 獲取視頻的size，從而確定水印的位置
    AVAsset *asset = [AVAsset assetWithURL:videoURL];
    CGSize size = CGSizeZero;
    NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
    if (tracks.count > 0) {
        AVAssetTrack *videoTrack = tracks.firstObject;
        size = CGSizeMake(videoTrack.naturalSize.width, videoTrack.naturalSize.height);
    }

    // 文字水印（同理可添加圖片）
    UILabel *label = [[UILabel alloc] init];
    label.text = @"@Ander";
    label.font = kFontFromPx(100);
    label.textColor = kColorWithRGB(0xFFFFFF);
    label.textAlignment = NSTextAlignmentCenter;
    [label sizeToFit];
    label.frame = CGRectMake(size.width - label.size.width - 20, size.height - label.size.height - 20, label.size.width, label.size.height);
    // 將水印放在一個跟視頻大小相等的View上
    UIView *subView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)];
    [subView addSubview:label];
    
    _uiElement = [[GPUImageUIElement alloc] initWithView:subView];
    _blendFilter = [[GPUImageNormalBlendFilter alloc] init];
    GPUImageFilter* progressFilter = [[GPUImageFilter alloc] init];
    
    // 注意URL不要出錯补箍，不然下面會崩潰
    NSString *pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/Movie.mp4"];
    unlink([pathToMovie UTF8String]);   // 刪除當前該路徑下的文件
    NSURL *movieURL = [NSURL fileURLWithPath:pathToMovie];
    
    _movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:movieURL size:size];
    [progressFilter addTarget:_blendFilter];
    [_movieFile addTarget:progressFilter];
    [_uiElement addTarget:_blendFilter];
    
    _movieWriter.shouldPassthroughAudio = YES;
    // 判斷是否有音軌
    if ([asset tracksWithMediaType:AVMediaTypeAudio].count > 0){
        _movieFile.audioEncodingTarget = _movieWriter;
    } else {
        _movieFile.audioEncodingTarget = nil;
    }
    [_movieFile enableSynchronizedEncodingUsingMovieWriter:_movieWriter];
    [_blendFilter addTarget:_movieWriter];
    
    [_movieWriter startRecording];
    [_movieFile startProcessing];
    __weak typeof(self) weakSelf = self;
    //渲染
    [progressFilter setFrameProcessingCompletionBlock:^(GPUImageOutput *output, CMTime time) {
        dispatch_async(dispatch_get_main_queue(), ^{
            //水印可以移動
            CGRect frame = label.frame;
            frame.origin.x -= 1;
            frame.origin.y -= 1;
            label.frame = frame;
            //第5秒之后隱藏coverImageView2
            if (time.value/time.timescale>=5.0) {
                [label removeFromSuperview];
            }
        });
        // 這句必須有
        [weakSelf.uiElement update];
    }];

    [_movieWriter setCompletionBlock:^{
        dispatch_after(dispatch_time(DISPATCH_TIME_NOW, (int64_t)(0.2 * NSEC_PER_SEC)), dispatch_get_main_queue(), ^{
            __strong typeof(self) strongSelf = weakSelf;
            [strongSelf.blendFilter removeTarget:strongSelf.movieWriter];
            [strongSelf.movieWriter finishRecording];
            //保存相冊
            __block PHObjectPlaceholder *placeholder;
            if ([PHPhotoLibrary authorizationStatus] == PHAuthorizationStatusAuthorized) {
                if (UIVideoAtPathIsCompatibleWithSavedPhotosAlbum(pathToMovie)) {
                    NSError *error;
                    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
                        PHAssetChangeRequest* createAssetRequest = [PHAssetChangeRequest creationRequestForAssetFromVideoAtFileURL:movieURL];
                        placeholder = [createAssetRequest placeholderForCreatedAsset];
                    } error:&error];
                    if (error) {
                        kShowPopTip(nil, error.description, nil);
                    }else {
                        kShowPopTip(nil, @"視頻已保存到相冊", nil);
                    }
                }
            }
        });
    }];
}

參考文章：
http://www.hudongdong.com/ios/546.html