--- build/linux/unbundle/openh264.gn.orig	2023-01-17 19:19:00 UTC
+++ build/linux/unbundle/openh264.gn
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/buildflag_header.gni")
 import("//build/config/linux/pkg_config.gni")
 import("//build/shim_headers.gni")
 
@@ -33,4 +34,10 @@ source_set("processing") {
 source_set("encoder") {
   deps = [ ":openh264_shim" ]
   public_configs = [ ":config" ]
+}
+
+buildflag_header("buildflags") {
+  header = "buildflags.h"
+  header_dir = "third_party/openh264"
+  flags = [ "OPENH264_API_WELS=1" ]
 }