iOS 合并带有透明通道的视频-

视频的合成，透明通道是大家所熟知.

在图形图像学中，透明通道也称Alpha通道，代表数字图像中像素点的透明信息。白色的Alpha像素用以定义不透明的彩色像素，而黑色的Alpha定以透明像素，黑白之间的灰阶则是彩色图片中的半透明部分。-----摘自百度百科

所以在合并雪花，灯光，爆破。。。 这里就需要有透明通道的视频。

这里我用的是GPUImage 这个工具，可以讲雪花无缝隙的结合起来，说到这里，大家最好会使用一点ps，在图片滤镜处理的时候，可以通过ps来看看参数和效果

通过ps实验，发现滤色可以做到这一点。GPUImageScreenBlendFilter 可以结局这个事情。

详细的GPUImage的头文件点击这里----/article/8910323.html

_movieFile = [[GPUImageMovie alloc] initWithURL:url];

_movieFile.runBenchmark = YES;
_movieFile.playAtActualSpeed = NO;
_movieFile2 = [[GPUImageMovie alloc] initWithURL:url2];
_movieFile2.runBenchmark = YES;
_movieFile2.playAtActualSpeed = NO;
_filter = [[GPUImageScreenBlendFilter alloc] init];
//    filter = [[GPUImageUnsharpMaskFilter alloc] init];
[_movieFile addTarget:self.filter];
[_movieFile2 addTarget:self.filter];
// Only rotate the video for display, leave orientation the same for recording
// In addition to displaying to the screen, write out a processed version of the movie to disk
NSString *pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/last.mov"];
unlink([pathToMovie UTF8String]); // If a file already exists, AVAssetWriter won't let you record new frames, so delete the old movie

NSLog(@"file = %@",pathToMovie);
NSURL *movieURL = [NSURL fileURLWithPath:pathToMovie];

self.movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:movieURL size:CGSizeMake(640.0, 360.0)];
[self.filter addTarget:self.movieWriter];
// Configure this for video from the movie file, where we want to preserve all video frames and audio samples
self.movieWriter.shouldPassthroughAudio = YES;
//movieFile.audioEncodingTarget = self.movieWriter;
[_movieFile enableSynchronizedEncodingUsingMovieWriter:self.movieWriter];

[self.movieWriter startRecording];
[_movieFile startProcessing];
[_movieFile2 startProcessing];
__block mlkiMovie * sself = self;

[self.movieWriter setCompletionBlock:^{
[sself.filter removeTarget:sself.movieWriter];
[sself.movieFile endProcessing];
[sself.movieFile2 endProcessing];
[sself.movieWriter finishRecording];
NSLog(@"ok");
}];