视频播放抖动（播放一小段然后再从头播放完）

下面是放在pageViewController里面的子VC来播放视频。
模仿微信做的图片选择器，在浏览图片的时候，如果遇到视频，可以在浏览过程中播放视频。本人新手，希望遇到过这种情况的大神指教一下，谢谢了。

#import "CHVideoPlayerViewController.h"
#import

@interface CHVideoPlayerViewController ()
{
MPMoviePlayerViewController _movie;
UITapGestureRecognizer *_tap;
/*
* 播放按钮
*/
UIImageView *_playerView;

}
@end

@implementation CHVideoPlayerViewController

• (void)viewDidLoad {
  [super viewDidLoad];

  _tap = [[UITapGestureRecognizer alloc]initWithTarget:self action:@selector(tapAction:)];

  /**

  • 视频播放对象 */ _movie = [[MPMoviePlayerViewController alloc] initWithContentURL:_url]; _movie.moviePlayer.controlStyle = MPMovieControlStyleNone; [_movie.view setFrame:self.view.bounds]; _movie.view.autoresizingMask = UIViewAutoresizingFlexibleHeight|UIViewAutoresizingFlexibleWidth; _movie.moviePlayer.scalingMode = MPMovieScalingModeAspectFit; _movie.moviePlayer.shouldAutoplay = NO; [_movie.view.subviews.firstObject addGestureRecognizer:_tap];

  _playerView = [[UIImageView alloc]initWithImage:[UIImage imageNamed:@"bofang64"]];
  _playerView.backgroundColor = [UIColor clearColor];
  // [_playerView addGestureRecognizer:_tap];
  _playerView.center = _movie.view.center;
  [_movie.view addSubview:_playerView];

  [self.view addSubview:_movie.view];

  [[NSNotificationCenter defaultCenter] addObserver:self
  selector:@selector(myMovieFinishedCallback:)
  name:MPMoviePlayerPlaybackDidFinishNotification
  object:nil];

}

• (void)myMovieFinishedCallback:(NSNotification*)notification
  {
  _playerView.alpha = 1;
  self.navigationController.navigationBar.alpha = 0.5;
  self.navigationController.toolbar.alpha = 0.5;
  }

• (void)didReceiveMemoryWarning {
  [super didReceiveMemoryWarning];
  }

• (void)viewWillAppear:(BOOL)animated{
  [super viewWillAppear:animated];
  [_movie.moviePlayer prepareToPlay];

  if (_movie.moviePlayer.playbackState == MPMoviePlaybackStatePlaying) {
  self.navigationController.navigationBar.alpha = 0;
  self.navigationController.toolbar.alpha = 0;
  _playerView.alpha = 0;
  }else {
  self.navigationController.navigationBar.alpha = 0.5;
  self.navigationController.toolbar.alpha = 0.5;
  _playerView.alpha = 1;
  }

}

• (void)viewDidAppear:(BOOL)animated{
  [super viewDidAppear:animated];
  }

• (void)viewDidDisappear:(BOOL)animated{
  [super viewDidDisappear:animated];
  [_movie.moviePlayer stop];
  }

• (void)tapAction:(UITapGestureRecognizer *)tap {
  if (_movie.moviePlayer.playbackState == MPMoviePlaybackStatePlaying) {
  [_movie.moviePlayer pause];
  self.navigationController.navigationBar.alpha = 0.5;
  self.navigationController.toolbar.alpha = 0.5;
  _playerView.alpha = 1;
  }else {
  self.navigationController.navigationBar.alpha = 0;
  self.navigationController.toolbar.alpha = 0;
  [UIView animateWithDuration:0.5 animations:^{
  _playerView.alpha = 0;
  _playerView.transform = CGAffineTransformMakeScale(5, 5);
  } completion:^(BOOL finished) {
  _playerView.transform = CGAffineTransformIdentity;
  [_movie.moviePlayer play];
  }];

  }
  }