fix camera startup fallbacks

client/src/lib/camera.ts

@@ -9,6 +9,13 @@ export type CameraZoomState = {
   focusMode: string;
 };
 
+export type CameraRequestResult = {
+  stream: MediaStream;
+  appliedFacingMode: "user" | "environment";
+  audioEnabled: boolean;
+  usedFallback: boolean;
+};
+
 type NumericRange = {
   min: number;
   max: number;
@@ -66,6 +73,98 @@ export function getCameraVideoConstraints(
   }
 }
 
+function normalizeVideoConstraintCandidate(candidate: MediaTrackConstraints | true) {
+  if (candidate === true) {
+    return { label: "camera-any", video: true as const };
+  }
+
+  return {
+    label: JSON.stringify(candidate),
+    video: candidate,
+  };
+}
+
+function createFallbackVideoCandidates(
+  facingMode: "user" | "environment",
+  isMobile: boolean,
+  preset: CameraQualityPreset,
+) {
+  const base = getCameraVideoConstraints(facingMode, isMobile, preset);
+  const alternateFacing = facingMode === "environment" ? "user" : "environment";
+  const lowRes = {
+    facingMode,
+    width: { ideal: isMobile ? 640 : 960 },
+    height: { ideal: isMobile ? 360 : 540 },
+  } satisfies MediaTrackConstraints;
+  const lowResAlternate = {
+    facingMode: alternateFacing,
+    width: { ideal: isMobile ? 640 : 960 },
+    height: { ideal: isMobile ? 360 : 540 },
+  } satisfies MediaTrackConstraints;
+  const anyCamera = {
+    width: { ideal: isMobile ? 640 : 960 },
+    height: { ideal: isMobile ? 360 : 540 },
+  } satisfies MediaTrackConstraints;
+
+  const candidates = [
+    normalizeVideoConstraintCandidate(base),
+    normalizeVideoConstraintCandidate({
+      ...base,
+      frameRate: undefined,
+    }),
+    normalizeVideoConstraintCandidate(lowRes),
+    normalizeVideoConstraintCandidate(lowResAlternate),
+    normalizeVideoConstraintCandidate(anyCamera),
+    normalizeVideoConstraintCandidate(true),
+  ];
+
+  const deduped = new Map<string, { video: MediaTrackConstraints | true }>();
+  candidates.forEach((candidate) => {
+    if (!deduped.has(candidate.label)) {
+      deduped.set(candidate.label, { video: candidate.video });
+    }
+  });
+  return Array.from(deduped.values());
+}
+
+export async function requestCameraStream(options: {
+  facingMode: "user" | "environment";
+  isMobile: boolean;
+  preset: CameraQualityPreset;
+  audio?: false | MediaTrackConstraints;
+}) {
+  const videoCandidates = createFallbackVideoCandidates(options.facingMode, options.isMobile, options.preset);
+  const audioCandidates = options.audio ? [options.audio, false] : [false];
+  let lastError: unknown = null;
+
+  for (const audio of audioCandidates) {
+    for (let index = 0; index < videoCandidates.length; index += 1) {
+      const video = videoCandidates[index]?.video ?? true;
+      try {
+        const stream = await navigator.mediaDevices.getUserMedia({ video, audio });
+        const videoTrack = stream.getVideoTracks()[0] || null;
+        const settings = (
+          videoTrack && typeof (videoTrack as MediaStreamTrack & { getSettings?: () => unknown }).getSettings === "function"
+            ? (videoTrack as MediaStreamTrack & { getSettings: () => unknown }).getSettings()
+            : {}
+        ) as Record<string, unknown>;
+        const appliedFacingMode = settings.facingMode === "user" ? "user" : settings.facingMode === "environment" ? "environment" : options.facingMode;
+
+        return {
+          stream,
+          appliedFacingMode,
+          audioEnabled: stream.getAudioTracks().length > 0,
+          usedFallback: index > 0 || audio === false && Boolean(options.audio),
+        } satisfies CameraRequestResult;
+      } catch (error) {
+        lastError = error;
+      }
+    }
+  }
+
+  throw lastError instanceof Error ? lastError : new Error("无法访问摄像头");
+}
+
 export function getLiveAnalysisBitrate(preset: CameraQualityPreset, isMobile: boolean) {
   switch (preset) {
     case "economy":