如何在iPhone上录制视频时设置帧速率？

Question

我想写一个相机应用程序，使用iPhone的相机录制视频，但我找不到改变录制视频帧率的方法。例如，我想以每秒25帧而不是默认值30录制。

是否可以以任何方式设置此帧速率，如果是，如何？

Answer 1

据我所知，您不能设置FPS进行录制。查看AVFoundation的WWDC 2010视频。这似乎表明，只要我可以说，只能用于捕获帧数据。

我很想被证明是错误的，但我敢肯定，你不能。抱歉!

Answer 2

您可以使用AVCaptureConnection的videoMaxFrameDuration和videoMinFrameDuration属性。见http://developer.apple.com/library/ios/#DOCUMENTATION/AVFoundation/Reference/AVCaptureConnection_Class/Reference/Reference.html#//apple_ref/doc/uid/TP40009522

此外，还有一个问题，SO，解决这个（具有良好的代码示例）： I want to throttle video capture frame rate in AVCapture framework

Answer 3

您需要AVCaptureDevice.h

这里在这里工作代码：

- (void)attemptToConfigureFPS 
{ 

    NSError *error; 
    if (![self lockForConfiguration:&error]) { 
     NSLog(@"Could not lock device %@ for configuration: %@", self, error); 
     return; 
    } 

    AVCaptureDeviceFormat *format = self.activeFormat; 
    double epsilon = 0.00000001; 

    int desiredFrameRate = 30; 

    for (AVFrameRateRange *range in format.videoSupportedFrameRateRanges) { 

     NSLog(@"Pre Minimum frame rate: %f Max = %f", range.minFrameRate, range.maxFrameRate); 


     if (range.minFrameRate <= (desiredFrameRate + epsilon) && 
      range.maxFrameRate >= (desiredFrameRate - epsilon)) { 

      NSLog(@"Setting Frame Rate."); 

      self.activeVideoMaxFrameDuration = (CMTime){ 
       .value = 1, 
       .timescale = desiredFrameRate, 
       .flags = kCMTimeFlags_Valid, 
       .epoch = 0, 
      }; 
      self.activeVideoMinFrameDuration = (CMTime){ 
       .value = 1, 
       .timescale = desiredFrameRate, 
       .flags = kCMTimeFlags_Valid, 
       .epoch = 0, 
      }; 

      // self.activeVideoMinFrameDuration = self.activeVideoMaxFrameDuration; 

      // NSLog(@"Post Minimum frame rate: %f Max = %f", range.minFrameRate, range.maxFrameRate); 

      break; 
     } 
    } 

    [self unlockForConfiguration]; 


    // Audit the changes 
    for (AVFrameRateRange *range in format.videoSupportedFrameRateRanges) { 

     NSLog(@"Post Minimum frame rate: %f Max = %f", range.minFrameRate, range.maxFrameRate); 

    } 



}