Add Windows helper to prepend GStreamer bin to PATH

internal/utils/gstreamer_paths_windows.go

@@ -0,0 +1,58 @@
+//go:build windows
+
+package utils
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+// EnsureGStreamerOnPath best-effort prepends common GStreamer bin locations to PATH for the
+// current process. It does not modify system-wide PATH. This helps avoid missing-DLL issues
+// when users install GStreamer but its bin directory is not on PATH.
+func EnsureGStreamerOnPath() {
+	candidates := []string{}
+
+	// If the user set GSTREAMER_1_0_ROOT_X86_64, prefer its bin
+	if root := os.Getenv("GSTREAMER_1_0_ROOT_X86_64"); root != "" {
+		candidates = append(candidates, filepath.Join(root, "bin"))
+	}
+
+	// Common installer locations (64-bit)
+	candidates = append(candidates,
+		`C:\\gstreamer\\1.0\\msvc_x86_64\\bin`,
+		`C:\\Program Files\\GStreamer\\1.0\\msvc_x86_64\\bin`,
+	)
+
+	pathVal := os.Getenv("PATH")
+	parts := []string{}
+	seen := map[string]bool{}
+
+	// Prepend any found candidates that exist
+	for _, cand := range candidates {
+		if cand == "" {
+			continue
+		}
+		if _, err := os.Stat(cand); err == nil {
+			// Only add if not already present (case-insensitive on Windows)
+			lower := strings.ToLower(cand)
+			if !seen[lower] {
+				parts = append(parts, cand)
+				seen[lower] = true
+			}
+		}
+	}
+
+	// Append existing PATH entries, preserving order and deduping case-insensitively
+	for _, p := range filepath.SplitList(pathVal) {
+		lower := strings.ToLower(p)
+		if seen[lower] {
+			continue
+		}
+		parts = append(parts, p)
+		seen[lower] = true
+	}
+
+	_ = os.Setenv("PATH", strings.Join(parts, string(os.PathListSeparator)))
+}