使用alpha合成2个视频

Question

AVFoundation允许您将2个资源(2个视频)"组合"为2个"轨道",就像在Final Cut Pro中一样.

该理论说,我可以将两个视频叠加在一起,使用alpha,并查看两者.

我要么做错了,或者某处有错误,因为下面的测试代码虽然有点乱,但清楚地说明我应该看到2个视频,我只看到一个,如下所示:http://lockerz.com/s/172403384 - "蓝色"方块是IMG_1388.m4v

无论出于何种原因,IMG_1383.MOV永远不会显示.

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:YES], AVURLAssetPreferPreciseDurationAndTimingKey, nil];
AVMutableComposition *composition = [AVMutableComposition composition];
CMTimeRange timeRange = CMTimeRangeMake(kCMTimeZero, CMTimeMakeWithSeconds(4, 1));
AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];

// Track B
NSURL *urlVideo2 = [NSURL URLWithString:@"file://localhost/Users/me/Movies/Temp/IMG_1388.m4v"];
AVAsset *video2 = [AVURLAsset URLAssetWithURL:urlVideo2 options:options];
AVMutableCompositionTrack *videoTrack2 = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:0];
NSArray *videoAssetTracks2 = [video2 tracksWithMediaType:AVMediaTypeVideo];
AVAssetTrack *videoAssetTrack2 = ([videoAssetTracks2 count] > 0 ? [videoAssetTracks2 objectAtIndex:0] : nil);
[videoTrack2 insertTimeRange:timeRange ofTrack:videoAssetTrack2 atTime:kCMTimeZero error:&error];

AVMutableVideoCompositionLayerInstruction *to = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoAssetTrack2];
[to setOpacity:.5 atTime:kCMTimeZero];
[to setTransform:CGAffineTransformScale(videoAssetTrack2.preferredTransform, .5, .5) atTime:kCMTimeZero];

// Track A
NSURL *urlVideo = [NSURL URLWithString:@"file://localhost/Users/me/Movies/Temp/IMG_1383.MOV"];
AVURLAsset *video = [AVURLAsset URLAssetWithURL:urlVideo options:options];
AVMutableCompositionTrack *videoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:1];
NSArray *videoAssetTracks = [video tracksWithMediaType:AVMediaTypeVideo];
AVAssetTrack *videoAssetTrack = ([videoAssetTracks count] > 0 ? [videoAssetTracks objectAtIndex:0] : nil);
[videoTrack insertTimeRange:timeRange ofTrack:videoAssetTrack atTime:kCMTimeZero error:nil];

AVMutableVideoCompositionLayerInstruction *from = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoAssetTrack];
[from setOpacity:.5 atTime:kCMTimeZero];

// Video Compostion
AVMutableVideoCompositionInstruction *transition = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
transition.backgroundColor = [[UIColor clearColor] CGColor];
transition.timeRange = timeRange;
transition.layerInstructions = [NSArray arrayWithObjects:to, from, nil];
videoComposition.instructions = [NSArray arrayWithObjects:transition,  nil];
videoComposition.frameDuration = CMTimeMake(1, 30);
videoComposition.renderSize = CGSizeMake(480, 360);


// Export
NSURL *outputURL = [NSURL URLWithString:@"file://localhost/Users/me/Movies/Temp/export.MOV"];
AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:[[composition copy] autorelease] presetName:AVAssetExportPresetHighestQuality];
[exportSession setOutputFileType:@"com.apple.quicktime-movie"];
exportSession.outputURL = outputURL;
exportSession.videoComposition = videoComposition;
[exportSession exportAsynchronouslyWithCompletionHandler:nil];

// Player
AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:composition];
playerItem.videoComposition = videoComposition;
AVPlayer *player = [AVPlayer playerWithPlayerItem:playerItem];
AVPlayerLayer *playerLayer = [AVPlayerLayer playerLayerWithPlayer:player];

你看错了吗？

该代码的"目标"是"记录"摄像机输入(视频1)和opengl输出(视频2).我还尝试用"缓冲区"直接"组合"它们,但是我也是不成功的:(原来AVFoundation不像我想象的那么简单.

Answer 1

我认为你搞错了。

一个视频文件可能有多个数据流。例如，如果是有声视频，则该文件将有 2 个流：音频流和视频流。另一个示例是音频环绕视频文件，其可以包括5个或更多个音频流和1个视频流。

与音频一样，大多数视频文件容器格式（mov、mp4 等）支持 1 个文件中的多个视频流，但实际上这并不意味着这些流彼此之间有任何关系，它们只是被存储在同一个文件容器上。例如，如果您使用 QuickTime 打开此类文件，您将获得与此类文件上的视频流一样多的窗口。

无论如何，视频流不会以这种方式“混合”。您想要实现的目标与视频流的信号处理有关，我真的建议您阅读更多相关内容。

如果您确实不需要将视频数据“混合”到一个文件中，您可能希望使用 MPMediaPlayers 相互显示两个视频文件。请记住，处理视频数据通常是一个 CPU 密集型问题，您可能（有时）无法使用现在的 iOS 设备解决该问题。