视频裁剪，长度裁剪

//首先拿到要裁剪视频的url

AVAsset* asset = [AVAssetassetWithURL:self.outputUrl];

AVMutableComposition *composition = [AVMutableComposition composition];

[composition addMutableTrackWithMediaType:AVMediaTypeVideopreferredTrackID:kCMPersistentTrackID_Invalid];

AVAssetTrack *videoTrack = [[asset
tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];

//判断视频的方向，看是否需要旋转

UIInterfaceOrientation orientation = UIInterfaceOrientationPortrait;

NSArray *tracks = [asset
tracksWithMediaType:AVMediaTypeVideo];

if([tracks count] >0) {

AVAssetTrack *videoTrack = [tracks
objectAtIndex:0];

CGAffineTransform t = videoTrack.preferredTransform;

// Portrait

if(t.a ==0 && t.b ==1.0 && t.c == -1.0
&& t.d ==0) {

orientation = UIInterfaceOrientationPortrait;

}

// PortraitUpsideDown

if(t.a ==0 && t.b == -1.0 && t.c ==1.0
&& t.d ==0) {

orientation = UIInterfaceOrientationPortraitUpsideDown;

}

// LandscapeRight

if(t.a ==1.0 && t.b ==0 && t.c ==0
&& t.d ==1.0) {

orientation = UIInterfaceOrientationLandscapeRight;

}

// LandscapeLeft

if(t.a == -1.0 && t.b ==0 && t.c ==0
&& t.d == -1.0) {

orientation = UIInterfaceOrientationLandscapeLeft;

}

}

BOOL isPortrait = (orientation ==
UIInterfaceOrientationPortrait || orientation ==
UIInterfaceOrientationPortraitUpsideDown) ?
YES : NO;

//视频渲染大小，这里以4：3为例

CGFloat complimentSize = videoTrack.naturalSize.height *4 /3;

CGSize videoSize;

if(isPortrait) {

videoSize = CGSizeMake(videoTrack.naturalSize.height, complimentSize);

} else {

videoSize = CGSizeMake(complimentSize, videoTrack.naturalSize.height);

}

AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];

videoComposition.renderSize = videoSize;

videoComposition.frameDuration =
CMTimeMake(1,
30);

AVMutableVideoCompositionInstruction *instruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];

instruction.timeRange =
CMTimeRangeMake(kCMTimeZero,asset.duration);

// rotate and position video

AVMutableVideoCompositionLayerInstruction *transformer = [AVMutableVideoCompositionLayerInstructionvideoCompositionLayerInstructionWithAssetTrack:videoTrack];

CGFloat tx = (videoTrack.naturalSize.width-complimentSize)/2;

if (orientation ==UIInterfaceOrientationPortrait || orientation ==UIInterfaceOrientationLandscapeRight)
{

// invert translation

tx *= -1;

}

CGAffineTransform t1 =CGAffineTransformTranslate(videoTrack.preferredTransform, tx,0);

CGAffineTransform t2 =
CGAffineTransformTranslate(t1, isPortrait?0:videoTrack.naturalSize.width, isPortrait?videoTrack.naturalSize.height:0);

CGAffineTransform t3 =
CGAffineTransformScale(t2, isPortrait?1:-1, isPortrait?-1:1);

[transformer setTransform:t1
atTime:kCMTimeZero];

instruction.layerInstructions = [NSArray arrayWithObject: transformer];

videoComposition.instructions = [NSArray arrayWithObject: instruction];

// 设置要输出文件的位置

NSString* outputPath = [self.tempVideoPath stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.mp4",[TRCommonTool getCurrentDate]]];

NSURL *outPutUrl = [NSURL fileURLWithPath:outputPath];

if ([[NSFileManager defaultManager] fileExistsAtPath:outputPath]){

[[NSFileManager defaultManager] removeItemAtPath:outputPatherror:nil];

}

// export

AVAssetExportSession *exporter = [[AVAssetExportSessionalloc]initWithAsset:asset presetName:AVAssetExportPreset640x480];

exporter.videoComposition = videoComposition;

exporter.outputURL = outPutUrl;

exporter.outputFileType =AVFileTypeMPEG4;

exporter.shouldOptimizeForNetworkUse =true;

//开始时间，要裁剪的视频长度

CMTime beforeTime =
CMTimeMakeWithSeconds(beginSecond, 30);

CMTime rangeTime =
CMTimeMakeWithSeconds(timeRange, 30);

exporter.timeRange =
CMTimeRangeMake(beforeTime, rangeTime);

[exporter exportAsynchronouslyWithCompletionHandler:^{

AVAssetExportSessionStatus status = exporter.status;

//注意这里一定要回到主线程，因为该任务是在子线程

dispatch_async(dispatch_get_main_queue(), ^{

switch (status) {

caseAVAssetExportSessionStatusCompleted:{

//将视频存入系统相册 [[[ALAssetsLibraryalloc]init] writeVideoAtPathToSavedPhotosAlbum:outPutUrl completionBlock:^(NSURL
*assetURL,NSError *error) {

break;

}

caseAVAssetExportSessionStatusFailed:{

break;

}

default:{

HHLog(@"exporter%@",exporter.error);

break;

}

}

});

}];