1、如果想拿到 PHAsset

完全访问：

PHAsset *asset = info[UIImagePickerControllerPHAsset];

限制访问：

 info[UIImagePickerControllerPHAsset] = nil

2、想拿到视频时长

完全访问：

asset.duration;

限制访问：

NSURL *selectUrl = info[UIImagePickerControllerMediaURL];          NSDictionary *dic = @{AVURLAssetPreferPreciseDurationAndTimingKey:@(YES)};       AVURLAsset *audioAsset = [AVURLAsset URLAssetWithURL:selectUrl options:dic];             

CMTime audioDuration = audioAsset.duration;             audioDurationSeconds = CMTimeGetSeconds(audioDuration);