Make camera id optional

If no camera id is provided, use the first camera available.

app/src/cli.c

@@ -2205,12 +2205,6 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
             return false;
         }
 
-        if (!opts->camera_id) {
-            LOGE("Camera id must be specified by --camera-id=ID "
-                 "(list the available ids with --list-cameras)");
-            return false;
-        }
-
         if (!opts->camera_size) {
             LOGE("Camera size must be specified by --camera-size=WIDTHxHEIGHT");
             return false;

server/src/main/java/com/genymobile/scrcpy/CameraCapture.java

@@ -7,6 +7,7 @@ import android.annotation.TargetApi;
 import android.hardware.camera2.CameraAccessException;
 import android.hardware.camera2.CameraCaptureSession;
 import android.hardware.camera2.CameraDevice;
+import android.hardware.camera2.CameraManager;
 import android.hardware.camera2.CaptureFailure;
 import android.hardware.camera2.CaptureRequest;
 import android.hardware.camera2.params.OutputConfiguration;
@@ -49,12 +50,30 @@ public class CameraCapture extends SurfaceCapture {
         cameraExecutor = new HandlerExecutor(cameraHandler);
 
         try {
-            cameraDevice = openCamera(explicitCameraId);
+            String cameraId = selectCamera(explicitCameraId);
+            if (cameraId == null) {
+                throw new IOException("No matching camera found");
+            }
+
+            Ln.i("Using camera '" + cameraId + "'");
+            cameraDevice = openCamera(cameraId);
         } catch (CameraAccessException | InterruptedException e) {
             throw new IOException(e);
         }
     }
 
+    private String selectCamera(String explicitCameraId) throws CameraAccessException {
+        if (explicitCameraId != null) {
+            return explicitCameraId;
+        }
+
+        CameraManager cameraManager = ServiceManager.getCameraManager();
+
+        String[] cameraIds = cameraManager.getCameraIdList();
+        // Use the first one
+        return cameraIds.length > 0 ? cameraIds[0] : null;
+    }
+
     @Override
     public void start(Surface surface) throws IOException {
         try {