在Android系统中实现开机启动设备摄像头采集音视频流并设置相关参数的代码如下：

1. 创建一个BroadcastReceiver用于接收开机广播，并拉起后台服务：

public class BootCompletedReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        if (Intent.ACTION_BOOT_COMPLETED.equals(intent.getAction())) {
            // 拉起后台服务
            Intent serviceIntent = new Intent(context, CameraCaptureService.class);
            context.startForegroundService(serviceIntent);
        }
    }
}

1. 创建一个Service用于后台持续采集音视频流：

public class CameraCaptureService extends Service {

    private MediaProjectionManager mediaProjectionManager;
    private MediaRecorder mediaRecorder;
    private VirtualDisplay virtualDisplay;

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        startCameraCapture();
        return super.onStartCommand(intent, flags, startId);
    }

    @Override
    public void onDestroy() {
        stopCameraCapture();
        super.onDestroy();
    }

    private void startCameraCapture() {
        mediaProjectionManager = (MediaProjectionManager) getSystemService(Context.MEDIA_PROJECTION_SERVICE);

        // 获取屏幕录制权限，需要用户确认授权
        startActivityForResult(mediaProjectionManager.createScreenCaptureIntent(), REQUEST_MEDIA_PROJECTION);
        
        // 初始化MediaRecorder并设置参数
        mediaRecorder = new MediaRecorder();
        mediaRecorder.setAudioSource(MediaRecorder.AudioSource.MIC);
        mediaRecorder.setVideoSource(MediaRecorder.VideoSource.SURFACE);
        
        // 设置输出格式和编码器类型为H264，并设置相关参数
		mediaRecorder.setOutputFormat(MediaRecorder.OutputFormat.MPEG_4);
		mediaRecorder.setAudioEncoder(MediaRecorder.AudioEncoder.AAC);
		mediaRecorder.setVideoEncoder(MediaRecorder.VideoEncoder.H264);
        mediaRecorder.setOutputFile("保存文件路径");

        // 设置码率、I帧间隔、帧率、分辨率等参数
        mediaRecorder.setVideoEncodingBitRate(128000);  // 码率为128k
        mediaRecorder.setVideoFrameRate(25);  // 帧率为25
        mediaRecorder.setVideoSize(640, 480);  // 分辨率为640*480
        
        // 开启Smart编码，设置I帧间隔值为5秒
        mediaRecorder.setCaptureRate(mediaRecorder.getVideoFrameRate());
        mediaRecorder.setVideoIFrameInterval(5 * mediaRecorder.getVideoFrameRate());

        try {
            // 准备MediaRecorder并开始录制
            mediaRecorder.prepare();
            virtualDisplay = createVirtualDisplay();
            mediaRecorder.start();
            
            // 防止Service被销毁，调用startForeground方法使Service变成前台服务
            startForeground(1, new Notification());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void stopCameraCapture() {
        if (mediaProjectionManager != null && virtualDisplay != null) {
            virtualDisplay.release();
            mediaProjectionManager = null;
            virtualDisplay = null;
            
            if (mediaRecorder != null) {
                try {
                    // 停止录制，并释放资源
                    mediaRecorder.stop();
                    mediaRecorder.reset();
                    mediaRecorder.release();
                    mediaRecorder = null;
                } catch (IllegalStateException e) {
                    e.printStackTrace();
                }
            }
            
			// 移除前台服务通知并停止Service
			stopForeground(true);
			stopSelf();
        }
    }

    private VirtualDisplay createVirtualDisplay() {
        DisplayMetrics metrics = new DisplayMetrics();
        WindowManager windowManager = (WindowManager) getSystemService(Context.WINDOW_SERVICE);
        windowManager.getDefaultDisplay().getMetrics(metrics);
        
        // 获取MediaProjection并创建虚拟显示屏幕
		return mediaProjection.createVirtualDisplay(
				"ScreenCapture",
				640,
				480,
				metrics.densityDpi,
				DisplayManager.VIRTUAL_DISPLAY_FLAG_AUTO_MIRROR,
				mediaRecorder.getSurface(),
				null, null);
    }
    
    @Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		if (requestCode == REQUEST_MEDIA_PROJECTION && resultCode == RESULT_OK) {
			MediaProjection mediaProjection = mediaProjectionManager.getMediaProjection(resultCode, data);
            this.mediaProjection = mediaProjection;
		}
		super.onActivityResult(requestCode, resultCode, data);
	}

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }
}

1. 在AndroidManifest.xml中注册相关组件：

<uses-permission android:name="android.permission.RECORD_AUDIO"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

<application ...>
   ...
   
   <receiver android:name=".BootCompletedReceiver">
      <intent-filter>
         <action android:name="android.intent.action.BOOT_COMPLETED"/>
      </intent-filter>
   </receiver>

   ...
</application>

请根据需求自行替换代码中的保存文件路径和其他必要参数，并确保已申请相应权限。此代码仅提供一个示例，实际使用时需要根据具体需求进行修改和完善。


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