兼容前置后置摄像头

src/views/step2.vue

@@ -168,8 +168,9 @@ async function videoUrlToBlob(videoUrl: string): Promise<Blob> {
   return res.blob();
 }
 
-async function setupNativeRecorder() {
+type CameraFacing = 'front' | 'rear';
-  cameraReady.value = false;
+
+function getCameraPreviewLayout() {
   const vw = Math.round(window.innerWidth);
   const vh = Math.round(window.innerHeight);
   // 让预览按比例“contain”居中，避免满屏裁剪导致人脸变大
@@ -184,11 +185,18 @@ async function setupNativeRecorder() {
   const desiredCenterY = Math.round(vh * RETICLE_CENTER_Y);
   const pyRaw = Math.round(desiredCenterY - ph / 2);
   const py = Math.max(0, Math.min(vh - ph, pyRaw));
+  return { pw, ph, px, py };
+}
 
+async function setupNativeRecorder() {
+  cameraReady.value = false;
+  const { pw, ph, px, py } = getCameraPreviewLayout();
+
+  const startPreviewAndRecord = async (position: CameraFacing) => {
     await CameraPreview.start({
       parent: PREVIEW_ID,
       toBack: true,
-    position: 'front',
+      position,
       enableVideoMode: true,
       disableAudio: true,
       // 不铺满：按比例居中显示（可能出现上下/左右留黑边）
@@ -201,29 +209,34 @@ async function setupNativeRecorder() {
       rotateWhenOrientationChanged: true,
       force: true
     });
-
     await CameraPreview.startRecordVideo({});
+  };
+
+  let usedFacing: CameraFacing = 'front';
+  try {
+    await startPreviewAndRecord('front');
+  } catch (firstErr) {
+    console.warn('前置摄像头不可用，尝试后置:', firstErr);
+    try {
+      await CameraPreview.stop({ force: true });
+    } catch {
+      /* ignore */
+    }
+    await startPreviewAndRecord('rear');
+    usedFacing = 'rear';
+  }
+
   started = true;
   isRecording.value = true;
   cameraReady.value = true;
-  statusText.value = '前置摄像头录制中';
+  statusText.value ='前置摄像头录制中'
+   
 
   // 尺寸变化时同步更新原生预览，保持按比例居中
   const onResize = async () => {
     if (!Capacitor.isNativePlatform() || released) return;
     try {
-      const vw = Math.round(window.innerWidth);
+      const { pw, ph, px, py } = getCameraPreviewLayout();
-      const vh = Math.round(window.innerHeight);
-      let pw = vw;
-      let ph = Math.round(pw * PREVIEW_ASPECT);
-      if (ph > vh) {
-        ph = vh;
-        pw = Math.round(ph / PREVIEW_ASPECT);
-      }
-      const px = Math.round((vw - pw) / 2);
-      const desiredCenterY = Math.round(vh * RETICLE_CENTER_Y);
-      const pyRaw = Math.round(desiredCenterY - ph / 2);
-      const py = Math.max(0, Math.min(vh - ph, pyRaw));
       await CameraPreview.setPreviewSize({
         width: pw,
         height: ph,