最近项目中需要用到视频拍摄和上传
拍摄界面参考的是微信朋友圈发视频的界面

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拍摄完视频正常的逻辑应该是压缩，然后上传
但是在我压缩完并上传之后，在后台查看上传的视频，经验是倒着的！旋转了90度
既然旋转了90度，那我们再把它旋转回来就可以了呗

直接上代码吧，也没有什么注释，因为懒(这个方法同时包含了压缩和旋转)

+(void)lowQuailtyWithInputURL:(NSURL *)inputURL blockHandler:(void (^)(BOOL, AVAssetExportSession *, NSURL *))handler
{
    AVURLAsset *asset = [AVURLAsset URLAssetWithURL:inputURL options:nil];
    AVAssetExportSession *session = [[AVAssetExportSession alloc] initWithAsset:asset presetName:AVAssetExportPresetMediumQuality];
    NSString *path = [NSString stringWithFormat:@"%@VideoCompression/",NSTemporaryDirectory()];
    
    NSFileManager *fileManage = [[NSFileManager alloc] init];    static dispatch_once_t predicate;
    dispatch_once(&predicate, ^{
        if(![fileManage fileExistsAtPath:path]){
            [fileManage createDirectoryAtPath:path withIntermediateDirectories:YES attributes:nil error:nil];
        }
    });
    if([fileManage fileExistsAtPath:[NSString stringWithFormat:@"%@VideoCompressionTemp.mp4",path]]){
        [fileManage removeItemAtPath:[NSString stringWithFormat:@"%@VideoCompressionTemp.mp4",path] error:nil];
    }
    
    NSURL *compressionVideoURL = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@VideoCompressionTemp.mp4",path]];
    session.outputURL = compressionVideoURL;
    session.outputFileType = AVFileTypeMPEG4;
    session.shouldOptimizeForNetworkUse = YES;
    session.videoComposition = [VideoEditingView getVideoComposition:asset];
    [session exportAsynchronouslyWithCompletionHandler:^{
        dispatch_async(dispatch_get_main_queue(),^{
            switch ([session status]) {
                case AVAssetExportSessionStatusFailed:{
                    NSLog(@"Export failed: %@ : %@", [[session error] localizedDescription], [session error]);
                    handler(NO,nil, nil);
                    break;
                }case AVAssetExportSessionStatusCancelled:{
                    NSLog(@"Export canceled");
                    handler(NO,nil, nil);
                    break;
                }default:
                    handler(YES,session,compressionVideoURL);
                    break;
            }
        });
    }];

}
+ (AVMutableVideoComposition *)getVideoComposition:(AVAsset *)asset {
    AVAssetTrack *videoTrack = [[asset tracksWithMediaType:AVMediaTypeVideo] objectAtIndex:0];
    AVMutableComposition *composition = [AVMutableComposition composition];
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    CGSize videoSize = videoTrack.naturalSize;
    
    NSArray *tracks = [asset tracksWithMediaType:AVMediaTypeVideo];
    if([tracks count] > 0) {
        AVAssetTrack *videoTrack = [tracks objectAtIndex:0];
        CGAffineTransform t = videoTrack.preferredTransform;
        if((t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0)){
            videoSize = CGSizeMake(videoSize.height, videoSize.width);
        }
    }
    composition.naturalSize    = videoSize;
    videoComposition.renderSize = videoSize;
    videoComposition.frameDuration = CMTimeMakeWithSeconds( 1 / videoTrack.nominalFrameRate, 600);
    
    AVMutableCompositionTrack *compositionVideoTrack;
    compositionVideoTrack = [composition addMutableTrackWithMediaType:AVMediaTypeVideo preferredTrackID:kCMPersistentTrackID_Invalid];
    [compositionVideoTrack insertTimeRange:CMTimeRangeMake(kCMTimeZero, asset.duration) ofTrack:videoTrack atTime:kCMTimeZero error:nil];
    AVMutableVideoCompositionLayerInstruction *layerInst;
    layerInst = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
    [layerInst setTransform:videoTrack.preferredTransform atTime:kCMTimeZero];
    AVMutableVideoCompositionInstruction *inst = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
    inst.timeRange = CMTimeRangeMake(kCMTimeZero, asset.duration);
    inst.layerInstructions = [NSArray arrayWithObject:layerInst];
    videoComposition.instructions = [NSArray arrayWithObject:inst];
    return videoComposition;
}

就这样