//m4v、mov转MP4

- (void)m4vTomp4 {
    //[MBProgressHUD showMessage:@"正在上传..."];
    
    AVURLAsset *avAsset = [AVURLAsset URLAssetWithURL:[NSURL fileURLWithPath:_playPath] options:nil];
    NSArray *compatiblePresets = [AVAssetExportSession exportPresetsCompatibleWithAsset:avAsset];
    

    NSString *fileName=[NSString stringWithFormat:@"%f",[[NSDate date] timeIntervalSince1970]];
    
    if ([compatiblePresets containsObject:AVAssetExportPresetLowQuality])
        
    {
        
        AVAssetExportSession *exportSession = [[AVAssetExportSession alloc]initWithAsset:avAsset presetName:AVAssetExportPresetPassthrough];
        NSString *exportPath = [NSString stringWithFormat:@"%@/%@.mp4",
                                [NSHomeDirectory() stringByAppendingString:@"/tmp"],
                                fileName];
        exportSession.outputURL = [NSURL fileURLWithPath:exportPath];
        NSLog(@"exportPath :%@", exportPath);
        exportSession.outputFileType = AVFileTypeMPEG4;
        [exportSession exportAsynchronouslyWithCompletionHandler:^{
            
            switch ([exportSession status]) {
                case AVAssetExportSessionStatusFailed:
                    NSLog(@"Export failed: %@", [[exportSession error] localizedDescription]);
                    break;
                case AVAssetExportSessionStatusCancelled:
                    NSLog(@"Export canceled");
                    break;
                case AVAssetExportSessionStatusCompleted:
                    NSLog(@"转换成功");
                    
                    _playPath =exportPath;
                    
                    break;
                default:
                    break;
            }
        }];
    }
}