Couldn't write a frame when i swich background to foreground

[zj381652512]

when i swicth to background and foreground, i find that can not write a video frame...because GPUImageMovieWriter's assetWriter status is AVAssetWriterStatusFailed,

this my code:

#import "ZJCaptureVC.h"
#import "NSTimer+ZJWeakTimer.h"
#import "GPUImage.h"

@interface ZJCaptureVC ()
// GPUImage
@Property (nonatomic, strong) GPUImageVideoCamera *videoCamera;
@Property (nonatomic, strong) GPUImageOutput *filter;
@Property (nonatomic, strong) GPUImageMovieWriter *movieWriter;
@Property (nonatomic, strong) GPUImageView *filterView;
// UI
@Property (weak, nonatomic) IBOutlet UILabel *mLabel;
@Property (nonatomic, weak) NSTimer *mTimer;
@Property (nonatomic, assign) long mLabelTime;
@Property (weak, nonatomic) IBOutlet UIButton *endBtn;
// status
@Property (nonatomic, assign) BOOL recording;
// path
@Property (nonatomic, strong) NSString *pathToMovie;

@EnD

@implementation ZJCaptureVC

• (NSString *)pathToMovie {
  if (!_pathToMovie) {
  _pathToMovie = [NSHomeDirectory() stringByAppendingPathComponent:@"Documents/recordingmovie.mp4"];
  }
  return _pathToMovie;
  }

• (void)viewDidLoad {
  [super viewDidLoad];

  _videoCamera = [[GPUImageVideoCamera alloc] initWithSessionPreset:AVCaptureSessionPreset640x480 cameraPosition:AVCaptureDevicePositionBack];
  _videoCamera.outputImageOrientation = [UIApplication sharedApplication].statusBarOrientation;

  _filter = [[GPUImageSepiaFilter alloc] init];
  _filterView = [[GPUImageView alloc] initWithFrame:self.view.bounds];
  [self.view insertSubview:_filterView atIndex:0];

  [_videoCamera addTarget:_filter];
  [_filter addTarget:_filterView];
  [_videoCamera startCameraCapture];
  }

#pragma mark - Actions

• (IBAction)backClick:(UIButton *)sender {
  [self.navigationController popViewControllerAnimated:YES];
  }

• (IBAction)endClick:(UIButton *)sender {
  [self endRecording];
  }

• (IBAction)startClick:(UIButton *)sender {
  sender.selected = !sender.selected;
  if (sender.selected) {
  [self startRecording];
  } else {
  [self pauseRecording];
  }
  }

• (void)onTimer:(id)sender {
  _mLabel.text = [NSString stringWithFormat:@"录制时间:%lds", _mLabelTime++];
  }

#pragma mark - Private

• (void)setRecording:(BOOL)recording {
  _recording = recording;
  _endBtn.hidden = !recording;
  }

// 开始录制

• (void)startRecording {
  if (self.recording) {
  self.movieWriter.paused = NO;
  } else {
  // 如果已经存在文件，AVAssetWriter会有异常,删除旧文件
  NSURL *movieURL = [NSURL fileURLWithPath:self.pathToMovie];
  unlink([self.pathToMovie UTF8String]);

    // 视频设置
    CGFloat width  = 480.f;
    CGFloat height = 640.f;
    NSInteger numPixels     = width * height;
    CGFloat bitsPerPixel    = 6.0;
    NSInteger bitsPerSecond = numPixels * bitsPerPixel;
  
    // 码率和帧率设置
    NSDictionary *compressionProperties =
        @{ AVVideoAverageBitRateKey: @(bitsPerSecond),
           AVVideoExpectedSourceFrameRateKey: @(30),
           AVVideoMaxKeyFrameIntervalKey: @(30),
           AVVideoProfileLevelKey: AVVideoProfileLevelH264BaselineAutoLevel };
  
    // 视频属性
    NSDictionary *videoCompressionSettings =
        @{ AVVideoCodecKey: AVVideoCodecH264,
           AVVideoScalingModeKey: AVVideoScalingModeResizeAspectFill,
           AVVideoWidthKey: @(width),
           AVVideoHeightKey: @(height),
           AVVideoCompressionPropertiesKey: compressionProperties };
  
    // 创建_movieWriter
    _movieWriter = [[GPUImageMovieWriter alloc] initWithMovieURL:movieURL size:CGSizeMake(480.0, 640.0) fileType:AVFileTypeMPEG4 outputSettings:videoCompressionSettings];
    _movieWriter.encodingLiveVideo   = YES;
    _videoCamera.audioEncodingTarget = _movieWriter;
    [_filter addTarget:_movieWriter];
    [_movieWriter startRecording];
  
    self.recording = YES;
  

  }
  // 计时
  _mTimer = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(onTimer:) userInfo:nil repeats:YES];
  [self onTimer:nil];
  }

// 暂停

• (void)pauseRecording {
  if (!self.recording) {
  NSLog(@"还没开始录制");
  return;
  }
  if (_mTimer) {
  [_mTimer invalidate];
  }
  _movieWriter.paused = YES;
  }

// 完成录制

• (void)endRecording {
  if (!self.recording) {
  NSLog(@"还没开始录制");
  return;
  }
  if (_mTimer) {
  [_mTimer invalidate];
  }
  [_filter removeTarget:_movieWriter];
  _videoCamera.audioEncodingTarget = nil;

  [_movieWriter finishRecording];
  self.recording = NO;

  if (self.completionHandler) {
  self.completionHandler(self.pathToMovie);
  }
  [self.navigationController popViewControllerAnimated:YES];
  }

@EnD

[zj381652512]

GPUImageMovieWriter's assetWriter status is AVAssetWriterStatusFailed when app enter background...so we can solve it as below:

• (void)willEnterBackground:(NSNotification *)notification {
  __weak typeof(self)weakSelf = self;
  UIApplication *app = [UIApplication sharedApplication];
  self.backgroundRenderingID = [app beginBackgroundTaskWithExpirationHandler:^{
  [app endBackgroundTask:weakSelf.backgroundRenderingID];
  weakSelf.backgroundRenderingID = UIBackgroundTaskInvalid;
  }];
  }