ios - 使用 CABasicAnimation animationWithKeyPath : @"contents" on CATextLayer to display dynamic overlay text on Video

Question

我正在开发一款可向视频添加动态文本(如字幕)的应用程序。有许多类似的问题，但没有一个真正有一个有效的答案。我对使用“ContentAnimate”而不是“contents”作为基于 Synchronising image, text, and positioning with CoreAnimation 的 animationKeyPath 寄予厚望。但这对我不起作用。

我可以让文本作为叠加层显示在视频上，但动画不起作用 - 我总是看到来自 CATextLayer 的原始基本文本。以下是我如何设置字幕和覆盖:

        // 1 - Set up the text layer
        CATextLayer *subtitle1Text = [[CATextLayer alloc] init];
        [subtitle1Text setFont:@"Helvetica-Bold"];
        //[subtitle1Text setString:[NSString stringWithFormat:@"%@: %@",  bookmark.creatorMonkeyName, bookmark.info]];
        [subtitle1Text setString:@"Place holder"];

        [subtitle1Text setFontSize:36];
        [subtitle1Text setFrame:CGRectMake(0, 0, videoSize.width, 100)];
        [subtitle1Text setAlignmentMode:kCAAlignmentCenter];
        [subtitle1Text setForegroundColor:[[UIColor whiteColor] CGColor]];


        // 2 - The  overlay
        CALayer *overlayLayer = [CALayer layer];
        [overlayLayer addSublayer:subtitle1Text];
        overlayLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
        [overlayLayer setMasksToBounds:YES];
        overlayLayer.hidden = YES;

        CALayer *parentLayer = [CALayer layer];
        CALayer *videoLayer = [CALayer layer];
        parentLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);
        videoLayer.frame = CGRectMake(0, 0, videoSize.width, videoSize.height);

        [parentLayer addSublayer:videoLayer];
        [parentLayer addSublayer:overlayLayer];
        videoComp.renderSize = videoSize;
        videoComp.frameDuration = CMTimeMake(1, (int32_t) fps);

这是我添加动画的方法:

            CABasicAnimation *showCommentAnimation2 = [CABasicAnimation animationWithKeyPath:@"contents"];

            [CATransaction begin];
            [CATransaction setDisableActions:YES];

            overlayLayer.hidden = NO;
            showCommentAnimation2.fromValue = @"Hello";
            showCommentAnimation2.toValue = @"Goodbye";
            showCommentAnimation2.beginTime = bookmark.relativeTimeStamp;
            showCommentAnimation2.duration = commentTimeDisplayed;
            [subtitle1Text addAnimation:showCommentAnimation2 forKey:[@(i) stringValue]]; //"i" is an iterator, This should allow multiple animations of the same type
            [CATransaction setDisableActions:NO];
            [CATransaction commit];

副标题弹出并消失 - 但我总是看到文本“占位符”，而不是“你好”或“再见”。

我使用以下方法将视频导出到相机胶卷:

        videoComp.animationTool = [AVVideoCompositionCoreAnimationTool
                                   videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
    _assetExport.videoComposition = videoComp;
    _assetExport.outputFileType = @"public.mpeg-4";
    _assetExport.outputURL = outputFileUrl;
    [_assetExport exportAsynchronouslyWithCompletionHandler:
     ^(void ) {
         if (AVAssetExportSessionStatusCompleted == _assetExport.status) {
             DLog(@"AVAssetExportSessionStatusCompleted");
             ALAssetsLibrary *library = [[[ALAssetsLibrary alloc] init] autorelease];
             DLog(@"About to copy video to camera roll");
             //move video to camera roll

             [library writeVideoAtPathToSavedPhotosAlbum:outputFileUrl completionBlock:^(NSURL *assetURL, NSError *error) {
                 [self removeWaitingScreen];
                 dispatch_async(dispatch_get_main_queue(), ^(void){
                     MPMoviePlayerViewController* theMovie = [[MPMoviePlayerViewController alloc] initWithContentURL: assetURL];
                     [_viewController presentMoviePlayerViewControllerAnimated:theMovie];

                 });
             }];
         } else{
             // a failure may happen because of an event out of your control
             // for example, an interruption like a phone call comming in
             // make sure and handle this case appropriately
             DLog(@"Error - Export Session Status: %ld", (long)_assetExport.status);
             dispatch_async(dispatch_get_main_queue(), ^(void){
                 [self removeWaitingScreen];
                 [[[[UIAlertView alloc] initWithTitle:NSLocalizedString(@"Error", NSStringFromClass([self class]))
                                              message:NSLocalizedString(@"Video Creation Failed", nil)
                                             delegate:nil
                                    cancelButtonTitle:NSLocalizedString(@"OK", nil)
                                    otherButtonTitles: nil] autorelease] show];
             });
         }

   [videoComp release];
   }];

}];

有人能帮忙吗？

如果有更好的方法将字幕刻录到视频中，我愿意接受建议。

谢谢。

Answer 1

具有键路径 contents 的动画不能与字符串值(@"Hello" 和 @"Goodbye")一起使用。层的 contents 属性包含图像，可手动设置或由层本身绘制。

只需设置文本层的 string 属性就足以产生隐式动画。但是，听起来您需要一个明确的动画来控制 beginTime。这样做的方法是使用 CATransition .参见 here举个例子。