问题描述
AVFoundation可让您将2个资产（2部影片）「合成」为2个「曲目」，例如Final Cut Pro。
AVFoundation allows you to "compose" 2 assets (2 videos) as 2 "tracks", just like in Final Cut Pro, for example.
这个理论说，我可以有两个视频的顶部，用alpha，看到两个。
The theory says I can have 2 videos on top of each other, with alpha, and see both.
我做错了，或者在某处有一个错误，因为下面的测试代码虽然有些凌乱，但我清楚地说明我应该看到2个视频，只能看到一个，如下所示： - 蓝色方块是IMG_1388.m4v
Either I'm doing something wrong, or there's a bug somewhere, because the following test code, although a bit messy, clearly states I should see 2 videos, and I only see one, as seen here: http://lockerz.com/s/172403384 -- the "blue" square is IMG_1388.m4v
无论什么原因，IMG_1383.MOV都不会显示。
For whatever reason, IMG_1383.MOV is never shown.
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];
您看到错误吗？
该代码的目标是记录摄像机输入（视频1）和opengl输出（视频2）。我也试图直接缓冲他们缓冲区和所有这一切，但我还是不成功:(原来的AVFoundation比我想象的更不平凡。
The "goal" of this code is to "record" the camera input (video 1) and the opengl output (video 2). I also tried to "compose" them "directly" with Buffers and all that, but I was as well unsuccessful :( Turns out AVFoundation is way less trivial than I thought.
推荐答案
看起来不错，除了这一部分：
It looks good, except this part:
AVMutableVideoCompositionLayerInstruction *from = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoAssetTrack];
AVMutableVideoCompositionLayerInstruction *to = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoAssetTrack2];
使用 videoTrack 和 videoTrack2 来构建图层说明，即添加到 ，而不是原始资源 videoAssetTrack 和 videoAssetTrack2 。
You need to use videoTrack and videoTrack2 to build the layer instructions, i.e., the tracks added to composition, instead of the original assets videoAssetTrack and videoAssetTrack2.
此外，添加一个转换来旋转视频有点棘手（像AVFoundation超出了基础）。
Also, adding a transformation to rotate the video it's a bit trickier (like anything in AVFoundation beyond the basics).I've just commented out the line to make it play the 2 videos.
这是你的代码修改：
NSError *error = nil;
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 = [[NSBundle mainBundle] URLForResource:@"b" withExtension:@"mov"];
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:videoTrack2];
[to setOpacity:.5 atTime:kCMTimeZero];
//[to setTransform:CGAffineTransformScale(videoAssetTrack2.preferredTransform, .5, .5) atTime:kCMTimeZero];
// Track A
NSURL *urlVideo = [[NSBundle mainBundle] URLForResource:@"a" withExtension:@"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:videoTrack];
[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 = composition.naturalSize; // CGSizeMake(480, 360);
这篇关于合成2个视频在彼此顶部与alpha的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！