QTKit, как записать фильм в файл для определенной продолжительности

Question

QTKit, как записать фильм в файл для определенной продолжительности

У меня проблемы с тем, что я считаю легкой задачей.

Я пытаюсь записать видео с любой подключенной веб-камеры в файл в течение определенного времени. Но длительность, которая фактически записывается, всегда составляет около 3/4 секунды. Например, 5 секунд записывается как 4,28

Следуя советам Google и Googling, я увидел, что простой способ сделать это - использовать setMaximumRecordedDuration в выходной файл фильма, а затем прекратите захват в методе captureOutput делегата.

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

    // 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");

Затем в моем методе captureOutput делегата 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, я работаю над VideoSnap. Вы можете увидеть полный исходный код, скачать и открыть его в xCode с GitHub

3 вопроса;

как я могу установить setMaximumRecordedDuration чтобы сделать эту работу за 5 секунд
цикл выполнения, который у меня есть, сейчас взломан, но когда я использую, например, while(recordingFlag), захват никогда не начинается
это лучший способ сделать это? я должен считать кадры так или иначе?

Ниже вставленный вывод из вышеприведенного 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!)
(recorded (null)  - frameCount 4!)
(recorded (null)  - frameCount 5!)
(recorded (null)  - frameCount 6!)
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(recorded 0:00:00:00.00/1  - frameCount 24!)
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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

1

objective-c macos qtkit

Источник

user104751 28 авг '13 в 22:10

1 ответ

Решение

Другие вопросы по тегам objective-c macos qtkit

user104751 30 авг '13 в 10:12 2013-08-30 10:12 · Accepted Answer · 2013-08-30 10:12

Таким образом, я в основном понял это (с некоторой помощью другого разработчика iOS/Obj-C);

Было 2 проблемы с моим кодом;

Мне нужен был правильный цикл выполнения (вне основного потока), чтобы я мог начать сеанс захвата с камеры и не выходить сразу (или использовать цикл while). Для этого я добавил следующее в конце моего processArgs() метод
```
[[NSRunLoop currentRunLoop] run];
```
Я обнаружил, что использование объектов QTTime для измерения количества времени, которое я записал, было большим количеством проблем, чем мне нужно было иметь дело, поэтому вместо этого я выбрал простой NSDate объект (называется mRecordingStartedOnDate). Также, глядя на мой вывод, было ясно, что сессии / камере требуется некоторое время, чтобы прогреться, прежде чем начинается захват, и вывод записывается в файл. Поэтому я проверяю recordedFileSize сначала на файл, и начните отсчитывать время с этого момента. Все это происходит в моем методе делегата captureOutput следующим образом;
```
- (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 сделать рефакторинг, но код текущего состояния этого проекта здесь.

- Спасибо Полу Цочанарису за помощь!