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使用iPad Pro 9.7上的前置摄像头以60 FPS捕获视频

[英]Capturing video at 60 FPS with the front camera on iPad Pro 9.7"

 原文  2019-02-20 01:15:10  4   2    ios/ avfoundation/ frame-rate/ avcapturesession

问题描述

I am trying to configure the AVCaptureSession to grab frames at 640x480 at 60 FPS with the front camera on iPad Pro 9.7". 我正在尝试将AVCaptureSession配置为使用iPad Pro 9.7“上的前置摄像头以60 FPS抓取640x480的帧。

During the configuration I have these lines: 在配置过程中，我有以下几行： 

  for videoFormat in (captureDevice?.formats)! {

    let descriptions = videoFormat.formatDescription
    let dimensions = CMVideoFormatDescriptionGetDimensions(descriptions)
    let width = dimensions.width
    let height = dimensions.height

    if ((width != 640) || (height != 480)) {
      continue
    }
    //      let videoFormatDescriptionRef = videoFormat.formatDescription

    for range in videoFormat.videoSupportedFrameRateRanges {
      if range.maxFrameRate == 60 {
        bestFormat = videoFormat
        bestFrameRateRange = range
        break
      }
    }

    if ( bestFormat != nil) {
      captureDevice!.activeFormat = bestFormat!;
      captureDevice!.activeVideoMinFrameDuration = bestFrameRateRange!.minFrameDuration;
      captureDevice!.activeVideoMaxFrameDuration = bestFrameRateRange!.minFrameDuration;
      break
    }
  }

When I list the video formats supported by the camera I get this list: 当我列出摄像机支持的视频格式时，我得到以下列表： 

<AVCaptureDeviceFormat: 0x282fa1fc0 'vide'/'420v'  192x 144, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @6.67), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa1fb0 'vide'/'420f'  192x 144, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @6.67), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa1fa0 'vide'/'420v'  352x 288, { 2- 60 fps}, fov:49.895, max zoom:60.00 (upscales @3.33), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa1f90 'vide'/'420f'  352x 288, { 2- 60 fps}, fov:49.895, max zoom:60.00 (upscales @3.33), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa1f80 'vide'/'420v'  480x 360, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.67), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa1f70 'vide'/'420f'  480x 360, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.67), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa1f60 'vide'/'420v'  640x 480, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa1f50 'vide'/'420f'  640x 480, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa2030 'vide'/'420v'  960x 540, { 2- 60 fps}, fov:58.480, max zoom:48.50 (upscales @1.43), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa2040 'vide'/'420f'  960x 540, { 2- 60 fps}, fov:58.480, max zoom:48.50 (upscales @1.43), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa2050 'vide'/'420v' 1024x 768, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @1.25), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa2060 'vide'/'420f' 1024x 768, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @1.25), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa2070 'vide'/'420v' 1280x 720, { 2- 60 fps}, fov:58.480, max zoom:48.50 (upscales @1.08), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa2080 'vide'/'420f' 1280x 720, { 2- 60 fps}, fov:58.480, max zoom:48.50 (upscales @1.08), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color> 

<AVCaptureDeviceFormat: 0x282fa2090 'vide'/'420v' 1280x 960, { 2- 60 fps}, HRSI:2576x1932, fov:54.400, max zoom:60.00 (upscales @1.00), ISO:34.0-2176.0, SS:0.000013-0.500000> 

<AVCaptureDeviceFormat: 0x282fa20a0 'vide'/'420f' 1280x 960, { 2- 60 fps}, HRSI:2576x1932, fov:54.400, max zoom:60.00 (upscales @1.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports wide color>

Because I am particularly interested in 640x480, I will want one of these: 因为我对640x480特别感兴趣，所以我需要以下一种： 

<AVCaptureDeviceFormat: 0x282fa1f60 'vide'/'420v'  640x 480, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR> 

<AVCaptureDeviceFormat: 0x282fa1f50 'vide'/'420f'  640x 480, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR, supports wide color>

I choose the first one: 我选择第一个： 

<AVCaptureDeviceFormat: 0x282fa1f60 'vide'/'420v'  640x 480, { 2- 60 fps}, fov:54.400, max zoom:60.00 (upscales @2.00), ISO:34.0-2176.0, SS:0.000013-0.500000, supports HDR>

If I understood this correctly, if I choose this format I can set any frame rate I want between 2 and 60 FPS. 如果我理解正确，那么如果选择这种格式，则可以在2到60 FPS之间设置任何我想要的帧速率。

I choose 60 FPS, by setting these lines: 通过设置以下行，我选择60 FPS： 

  captureDevice!.activeVideoMinFrameDuration = bestFrameRateRange!.minFrameDuration;
  captureDevice!.activeVideoMaxFrameDuration = bestFrameRateRange!.minFrameDuration;

I have even tried this 我什至尝试过 

let fps60 = CMTimeMake(value: 1, timescale: 60)
captureDevice!.activeVideoMinFrameDuration = fps60;
captureDevice!.activeVideoMaxFrameDuration = fps60;

Whatever I do, video is always captured at 30 FPS. 无论我做什么，视频总是以30 FPS的速度捕获。

I am setting the capture session with 我正在设置捕获会话 

self.captureSession.sessionPreset = AVCaptureSession.Preset.vga640x480
let captureDevice = AVCaptureDevice.default(.builtInWideAngleCamera, for: AVMediaType.video, position: .front)

Note: I am not particularly interested by 640x480. 注意：我对640x480并不是特别感兴趣。 It only seemed to be the lightest resolution I could think that would make capture faster. 我认为这只是最轻的分辨率，可以使捕获更快。 I would go for any resolution that gives me 60 FPS on the front camera. 我会选择任何可以在前置摄像头上提供60 FPS的分辨率。

How can I do that? 我怎样才能做到这一点？

Thanks 谢谢

2 个解决方案

解决方案1
 0  2019-02-20 07:09:47

The following seems to be incorrect, because bestFrameRateRange!.minFrameDuration would have been 2? 以下内容似乎是不正确的，因为bestFrameRateRange!.minFrameDuration应该是2？ 

captureDevice!.activeVideoMinFrameDuration = bestFrameRateRange!.minFrameDuration;
captureDevice!.activeVideoMaxFrameDuration = bestFrameRateRange!.minFrameDuration;

Also, are you calling lockForConfiguration before you set the frame duration? 另外，在设置帧持续时间之前是否要调用lockForConfiguration ？ 

do {
    try captureDevice!.lockForConfiguration()
    let fps60 = CMTimeMake(value: 1, timescale: 60)
    captureDevice!.activeVideoMinFrameDuration = fps60;
    captureDevice!.activeVideoMaxFrameDuration = fps60;
    captureDevice!.unlockForConfiguration()
} catch {
    // handle error
}

解决方案2
 0 已采纳  2019-03-03 18:33:43

After a couple of days I found the problem. 几天后，我发现了问题。

You cannot use this line 您不能使用此行 

self.captureSession.sessionPreset = AVCaptureSession.Preset.vga640x480

after configuring the session or it will undo everything you do to some internal standard. 在配置会话之后，否则它将撤消您对某些内部标准所做的一切。

This line has to be one of the first things you do. 这行必须是您要做的第一件事。

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