QTKit, как записывать фильм в файл в течение определенной продолжительности

Question

У меня возникли проблемы с тем, что, по моему мнению, должно быть легкой задачей.

Я пытаюсь записать видео с любой прикрепленной веб-камеры в файл в течение определенной продолжительности. Но время, которое фактически записывается, всегда составляет около 3/4 секунды. Например. 5 секунд регистрируются как 4,28

После некоторого совета от погуглить и StackOverflow-ков, я видел, что простой способ сделать это состоит в использовании setMaximumRecordedDuration на выходной файл фильма, а затем остановить запись в метод захвата делегата.

Например, для захвата 5 секунд видео я использую следующий код прямо сейчас;

// set maximum duration (e.g. 5 secs at 30000 timescale) ?? 
    [mCaptureMovieFileOutput recordToOutputFileURL:[NSURL fileURLWithPath:path]]; 
    [mCaptureMovieFileOutput setMaximumRecordedDuration: QTMakeTime(5*30000, 30000)]; 
    [mCaptureSession startRunning]; 

    // start a run loop (for how long?) 
    verbose("(recording for %.2lf seconds)\n", [recordSeconds doubleValue]); 
    NSDate *now = [[NSDate alloc] init]; 
    [[NSRunLoop currentRunLoop] runUntilDate:[now dateByAddingTimeInterval: [recordSeconds doubleValue]]]; 
    verbose("(recording period ended)\n"); 

Тогда в моем captureOutput делегат метод у меня есть;

- (BOOL)captureOutput:(QTCaptureFileOutput *)captureOutput shouldChangeOutputFileAtURL:(NSURL *)outputFileURL forConnections:(NSArray *)connections dueToError:(NSError *)error { 
    QTTime durationRecorded = [mCaptureMovieFileOutput recordedDuration]; 
    NSString *outputDuration = QTStringFromTime(durationRecorded); 
    verbose("(capture output reached %s !)\n", [outputDuration UTF8String]); 

    [mCaptureMovieFileOutput recordToOutputFileURL:nil]; 

    return YES; 
} 

Полный код для этого здесь; https://github.com/matthutchinson/videosnap/blob/master/videosnap/videosnap.m

Этот код является частью нового приложения командной строки с открытым исходным кодом, над которым я работаю над VideoSnap. Вы можете увидеть полный исходный код, загрузить и открыть его в xCode от GitHub

3 вопроса;

• , как я могу установить setMaximumRecordedDuration, чтобы сделать эту работу в течение 5 секунд
• цикл запуска у меня есть хак прямо сейчас, но когда я использую, например, в то время как (recordFlag) захват никогда не начинается
• это лучший способ сделать это? следует ли считать кадры каким-то образом или что-то еще?

Ниже приведена вставка вышеназванного кода;

(no filename specified, using default) 
(no device specified, using default) 
(options before recording) 
    delay: 0.00s 
    record: 10.00s 
    filename: movie.mov 
    device: Built-in iSight 
(no delay) 
(starting device...) 
(recording for 10.00 seconds) 
(recorded (null) - frameCount 0!) 
(recorded (null) - frameCount 1!) 
(recorded (null) - frameCount 2!) 
(recorded (null) - frameCount 3!) 
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(recorded 0:00:00:04.28000/30000 - frameCount 280!) 
(recorded 0:00:00:04.28000/30000 - frameCount 281!) 
(capture output reached 0:00:00:04.28000/30000 !) 
(recorded 0:00:00:05.00/30000 - frameCount 282!) 
(recorded 0:00:00:05.00/30000 - frameCount 283!) 
(recorded 0:00:00:05.00/30000 - frameCount 284!) 
(recorded 0:00:00:05.00/30000 - frameCount 285!) 
(finished writing to movie file duration was 0:00:00:05.00/30000 !) 
(stopping session) 
(recording period ended) 
DONE! movie.mov 

Answer 1

Так что я в принципе понял это (с некоторой помощью от другого разработчика iOS/Obj-C);

Были проблемы с моим кодом;

• мне нужен правильный цикл запуска (вне основного потока) должен быть запущен, так что я могу начать свой захват сессии с камерой и не выйти сразу (или использовать время цикла). Для этого я добавил следующее в конце моего processArgs() метода

  [[NSRunLoop currentRunLoop] run]; 
  

• я обнаружил, используя объекты QTTime для измерения количества времени я записал было больше проблем, чем мне нужно, чтобы иметь дело с, так что вместо этого я выбрал для простого объекта NSDate (называемый mRecordingStartedOnDate). Также, глядя на мой вывод, было ясно, что сеанс/камера занимает некоторое время, чтобы разогреться до начала захвата, и вывод записывается в файл. Поэтому сначала я проверяю файл recordedFileSize на файл и начинаю отсчет времени с этого момента.Все это происходит в моем методе делегата captureOutput, например;

  - (void)captureOutput:(QTCaptureFileOutput *)captureOutput didOutputSampleBuffer:(QTSampleBuffer *)sampleBuffer fromConnection:(QTCaptureConnection *)connection { 
      // check we have started to record some bytes (this allows us to wait for camera to warm up and start capturing) 
      long recordedBytes = [mCaptureMovieFileOutput recordedFileSize]; 
  
      if(mRecordingStartedOnDate != nil) { 
       // check if we have recorded enough video yet 
       float recordedSeconds = [[NSDate date] timeIntervalSinceDate:mRecordingStartedOnDate]; 
       verbose("(recorded %f seconds)\n", recordedSeconds); 
       if(recordedSeconds >= 5.0) { 
        // stop recording to the file 
        [mCaptureMovieFileOutput recordToOutputFileURL:nil]; 
       } 
      } else if(recordedBytes > 0) { 
       // set the start date when recording initiated 
       mRecordingStartedOnDate = [NSDate date]; 
      } 
  } 
  

Я могу реорганизовать вещи, но код current state of this project is here.

- Спасибо за помощь Paul Tsochantaris!