//优化视频旋转方向
- (AVMutableVideoComposition *)fixedCompositionWithAsset:(AVAsset *)videoAsset {
    AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    // 视频转向
    int degrees = [self degressFromVideoFileWithAsset:videoAsset];
    if (degrees != 0) {
        CGAffineTransform translateToCenter;
        CGAffineTransform mixedTransform;
        videoComposition.frameDuration = CMTimeMake(1, 30);
        
        NSArray *tracks = [videoAsset tracksWithMediaType:AVMediaTypeVideo];
        AVAssetTrack *videoTrack = [tracks objectAtIndex:0];
        
        if (degrees == 90) {
            // 顺时针旋转90°
            translateToCenter = CGAffineTransformMakeTranslation(videoTrack.naturalSize.height, 0.0);
            mixedTransform = CGAffineTransformRotate(translateToCenter,M_PI_2);
            videoComposition.renderSize = CGSizeMake(videoTrack.naturalSize.height,videoTrack.naturalSize.width);
        } else if(degrees == 180){
            // 顺时针旋转180°
            translateToCenter = CGAffineTransformMakeTranslation(videoTrack.naturalSize.width, videoTrack.naturalSize.height);
            mixedTransform = CGAffineTransformRotate(translateToCenter,M_PI);
            videoComposition.renderSize = CGSizeMake(videoTrack.naturalSize.width,videoTrack.naturalSize.height);
        } else {
            // 顺时针旋转270°
            translateToCenter = CGAffineTransformMakeTranslation(0.0, videoTrack.naturalSize.width);
            mixedTransform = CGAffineTransformRotate(translateToCenter,M_PI_2*3.0);
            videoComposition.renderSize = CGSizeMake(videoTrack.naturalSize.height,videoTrack.naturalSize.width);
        }
        
        AVMutableVideoCompositionInstruction *roateInstruction = [AVMutableVideoCompositionInstruction videoCompositionInstruction];
        roateInstruction.timeRange = CMTimeRangeMake(kCMTimeZero, [videoAsset duration]);
        AVMutableVideoCompositionLayerInstruction *roateLayerInstruction = [AVMutableVideoCompositionLayerInstruction videoCompositionLayerInstructionWithAssetTrack:videoTrack];
        
        [roateLayerInstruction setTransform:mixedTransform atTime:kCMTimeZero];
        
        roateInstruction.layerInstructions = @[roateLayerInstruction];
        // 加入视频方向信息
        videoComposition.instructions = @[roateInstruction];
    }
    return videoComposition;
}

/// 获取视频角度
- (int)degressFromVideoFileWithAsset:(AVAsset *)asset {
    int degress = 0;
    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){
            // Portrait
            degress = 90;
        } else if(t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0){
            // PortraitUpsideDown
            degress = 270;
        } else if(t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0){
            // LandscapeRight
            degress = 0;
        } else if(t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0){
            // LandscapeLeft
            degress = 180;
        }
    }
    return degress;
}


/// 修正图片转向
- (UIImage *)fixOrientation:(UIImage *)aImage {
    
    if (aImage.imageOrientation == UIImageOrientationUp)
        return aImage;
    
    CGAffineTransform transform = CGAffineTransformIdentity;
    
    switch (aImage.imageOrientation) {
        case UIImageOrientationDown:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, aImage.size.height);
            transform = CGAffineTransformRotate(transform, M_PI);
            break;
            
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
            transform = CGAffineTransformRotate(transform, M_PI_2);
            break;
            
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, 0, aImage.size.height);
            transform = CGAffineTransformRotate(transform, -M_PI_2);
            break;
        default:
            break;
    }
    
    switch (aImage.imageOrientation) {
        case UIImageOrientationUpMirrored:
        case UIImageOrientationDownMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.width, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
            
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRightMirrored:
            transform = CGAffineTransformTranslate(transform, aImage.size.height, 0);
            transform = CGAffineTransformScale(transform, -1, 1);
            break;
        default:
            break;
    }
    
    CGContextRef ctx = CGBitmapContextCreate(NULL, aImage.size.width, aImage.size.height,
                                             CGImageGetBitsPerComponent(aImage.CGImage), 0,
                                             CGImageGetColorSpace(aImage.CGImage),
                                             CGImageGetBitmapInfo(aImage.CGImage));
    CGContextConcatCTM(ctx, transform);
    switch (aImage.imageOrientation) {
        case UIImageOrientationLeft:
        case UIImageOrientationLeftMirrored:
        case UIImageOrientationRight:
        case UIImageOrientationRightMirrored:
            // Grr...
            CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.height,aImage.size.width), aImage.CGImage);
            break;
            
        default:
            CGContextDrawImage(ctx, CGRectMake(0,0,aImage.size.width,aImage.size.height), aImage.CGImage);
            break;
    }
    
    CGImageRef cgimg = CGBitmapContextCreateImage(ctx);
    UIImage *img = [UIImage imageWithCGImage:cgimg];
    CGContextRelease(ctx);
    CGImageRelease(cgimg);
    return img;
    
}

摘自谭真--TZImagePickerController