设置60fps与闪光灯开启时AVCapturePhotoOutput拍照过曝求助

使用AVCapturePhotoOutput且将flashMode设为.on，同时将AVCaptureDevice的最低帧率设置为60fps时，拍摄的照片会出现严重过曝；相同配置下调至30fps时照片显示正常。尝试过多种AVCapturePhotoSettings配置均未解决问题，怀疑是iOS Bug，寻求解决建议。

复现代码 #

let settings = AVCapturePhotoSettings()
settings.flashMode = flashOn ? .on : .off
settings.isAutoVirtualDeviceFusionEnabled = true
settings.isAutoRedEyeReductionEnabled = true
self.photoOutput.capturePhoto(with: settings, delegate: self)

效果对比 #

• 60fps下的过曝照片：
  
• 30fps下的正常照片：
  

可行解决方向 #

1. 拍摄前临时切换帧率 #

在触发拍照操作前，将设备帧率临时切换到30fps区间，拍摄完成后再恢复原60fps设置，绕过高帧率与闪光灯的冲突：

// 拍摄前保存当前帧率配置
var originalMinFrameRate: Double? = nil
var originalMaxFrameRate: Double? = nil
guard let activeDevice = yourCaptureSession.inputs.compactMap({ $0 as? AVCaptureDeviceInput }).first?.device else { return }

do {
    try activeDevice.lockForConfiguration()
    originalMinFrameRate = activeDevice.activeVideoMinFrameRate
    originalMaxFrameRate = activeDevice.activeVideoMaxFrameRate
    // 切换到30fps固定帧率
    activeDevice.activeVideoMinFrameRate = 30
    activeDevice.activeVideoMaxFrameRate = 30
    activeDevice.unlockForConfiguration()
} catch {
    print("帧率切换失败：\(error.localizedDescription)")
}

// 执行拍照
self.photoOutput.capturePhoto(with: settings, delegate: self)

// 在拍照完成代理中恢复原帧率
func photoOutput(_ output: AVCapturePhotoOutput, didFinishProcessingPhoto photo: AVCapturePhoto, error: Error?) {
    guard let activeDevice = yourCaptureSession.inputs.compactMap({ $0 as? AVCaptureDeviceInput }).first?.device,
          let minRate = originalMinFrameRate, let maxRate = originalMaxFrameRate else { return }
          
    do {
        try activeDevice.lockForConfiguration()
        activeDevice.activeVideoMinFrameRate = minRate
        activeDevice.activeVideoMaxFrameRate = maxRate
        activeDevice.unlockForConfiguration()
    } catch {
        print("帧率恢复失败：\(error.localizedDescription)")
    }
}

2. 禁用虚拟设备融合算法 #

尝试关闭isAutoVirtualDeviceFusionEnabled，部分iOS设备在高帧率+闪光灯场景下，多摄像头融合算法可能出现测光异常：

settings.isAutoVirtualDeviceFusionEnabled = false

3. 指定照片编码格式 #

明确设置AVCapturePhotoSettings的编码格式，避免系统自动选择的格式与高帧率模式不兼容：

settings.preferredPhotoCodec = .jpeg // 或.hevc，根据设备支持情况选择

4. 提交Apple Bug反馈 #

如果以上方法均无效，说明这大概率是iOS系统层面的Bug，建议通过Apple开发者反馈平台提交报告，附上设备型号、iOS版本、完整复现步骤及对比照片，帮助Apple定位修复问题。

内容的提问来源于stack exchange，提问作者Jacob Zyla