视频压缩

            #import "ViewController.h"
            #import <AVFoundation/AVFoundation.h>

            @interface ViewController ()<UINavigationControllerDelegate, UIImagePickerControllerDelegate>
            @property (weak, nonatomic) IBOutlet UIImageView *imageView;

            @end

            @implementation ViewController

            - (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
            {
                UIImagePickerController *picker = [[UIImagePickerController alloc]init];
                
                picker.delegate = self;
                /*
                 UIImagePickerControllerSourceTypePhotoLibrary,  照片库 备份
                 UIImagePickerControllerSourceTypeCamera,  相机
                 UIImagePickerControllerSourceTypeSavedPhotosAlbum  相片库自己拍的
                 */
                NSLog(@"%@",[UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeSavedPhotosAlbum]);
                
                
                picker.sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;
                
                picker.mediaTypes = [UIImagePickerController availableMediaTypesForSourceType:UIImagePickerControllerSourceTypeSavedPhotosAlbum];
                
                [self presentViewController:picker animated:YES completion:nil];
                
                
            }

            - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
            {
                //获取视频地址
                NSURL  *movieUrl =  info[UIImagePickerControllerMediaURL];
               //压缩出来
                [self compressMovie:movieUrl];
                
            }
            //压缩方法
            - (void)compressMovie:(NSURL *)url
            {
                
                //1.创建一个素材(视频的url生成)对象
                AVAsset *asset = [AVAsset assetWithURL:url];
                
                //2.创建导出(低质量的导出就是压缩)回话
                AVAssetExportSession *session = [[AVAssetExportSession alloc]initWithAsset:asset presetName:AVAssetExportPresetMediumQuality];
                //AVAssetExportPresetLowQuality  3g  环境
                //AVAssetExportPresetMediumQuality  wifi 环境
                //AVAssetExportPresetHighestQuality  原来的质量没有必要压缩
                
                //保存的路
                NSString *path =  [NSTemporaryDirectory() stringByAppendingPathComponent:@"123.mov"];
                
                //删除之前可能存在的文件
                //如果不存在 这个文件  这个方法就啥都不做
                [[NSFileManager defaultManager]removeItemAtPath:path error:nil];
                
                
                //设置输出文件的url
                session.outputURL = [NSURL fileURLWithPath:path];
                
                //设置输出文件的类型
                session.outputFileType = AVFileTypeQuickTimeMovie;
                

                [session exportAsynchronouslyWithCompletionHandler:^{
                   
                    NSLog(@"导出完成! %@", [NSThread currentThread]);
                }];
            }

            - (void)viewDidLoad {
                [super viewDidLoad];
            }

            @end