diff --git a/local-tool/server/internal/camera/video_source.go b/local-tool/server/internal/camera/video_source.go
index 4502fa2..a26dd00 100644
--- a/local-tool/server/internal/camera/video_source.go
+++ b/local-tool/server/internal/camera/video_source.go
@@ -92,27 +92,53 @@ func NewVideoSourceFromURLWithSeek(rawURL string, fps float64, seekSeconds float
 // from platforms like YouTube, Vimeo, etc.
 // Returns the resolved direct URL or an error.
 func ResolveWithYTDLP(rawURL string) (string, error) {
-	// yt-dlp -f "best[ext=mp4]/best" --get-url <URL>
 	cmd := exec.Command("yt-dlp", "-f", "best[ext=mp4]/best", "--get-url", rawURL)
 	out, err := cmd.Output()
 	if err != nil {
 		if exitErr, ok := err.(*exec.ExitError); ok {
-			return "", fmt.Errorf("yt-dlp failed: %s", string(exitErr.Stderr))
+			stderr := strings.TrimSpace(string(exitErr.Stderr))
+			return "", fmt.Errorf("%s\n%s", friendlyYTDLPError(stderr), stderr)
 		}
-		return "", fmt.Errorf("yt-dlp not available: %w", err)
+		return "", fmt.Errorf("yt-dlp 未安裝或無法執行: %w", err)
 	}
 
 	resolved := strings.TrimSpace(string(out))
 	if resolved == "" {
-		return "", fmt.Errorf("yt-dlp returned empty URL")
+		return "", fmt.Errorf("yt-dlp 無法取得影片下載連結（影片可能有地區限制或需要登入）")
 	}
-	// yt-dlp may return multiple lines (video + audio); take only the first
 	if idx := strings.Index(resolved, "\n"); idx > 0 {
 		resolved = resolved[:idx]
 	}
 	return resolved, nil
 }
 
+// friendlyYTDLPError 把 yt-dlp 的技術性錯誤訊息轉成使用者能理解的提示。
+func friendlyYTDLPError(stderr string) string {
+	s := strings.ToLower(stderr)
+	switch {
+	case strings.Contains(s, "sign in") || strings.Contains(s, "age"):
+		return "此影片需要登入 YouTube 帳號才能觀看（例如年齡限制），無法直接使用"
+	case strings.Contains(s, "private"):
+		return "此影片為私人影片，無法存取"
+	case strings.Contains(s, "unavailable") || strings.Contains(s, "not available"):
+		return "此影片無法取得（可能已被移除或在你的地區不可用）"
+	case strings.Contains(s, "copyright"):
+		return "此影片因版權限制無法下載"
+	case strings.Contains(s, "live"):
+		return "此影片為直播串流，目前不支援直播推論"
+	case strings.Contains(s, "premiere"):
+		return "此影片為首播（Premiere），尚未開始或格式不支援"
+	case strings.Contains(s, "drm") || strings.Contains(s, "protected"):
+		return "此影片有 DRM 保護，無法下載"
+	case strings.Contains(s, "rate limit") || strings.Contains(s, "429"):
+		return "YouTube 暫時限制了請求頻率，請稍後再試"
+	case strings.Contains(s, "no video formats"):
+		return "找不到可用的影片格式"
+	default:
+		return "無法解析此影片連結，請確認 URL 是否正確且影片為公開狀態"
+	}
+}
+
 func newVideoSource(input string, fps float64, isURL bool, seekSeconds float64) (*VideoSource, error) {
 	if fps <= 0 {
 		fps = 15