diff --git a/third_party/blink/renderer/bindings/idl_in_modules.gni b/third_party/blink/renderer/bindings/idl_in_modules.gni
index 0fc128a231c4..71647554fbb8 100644
--- a/third_party/blink/renderer/bindings/idl_in_modules.gni
+++ b/third_party/blink/renderer/bindings/idl_in_modules.gni
@@ -1214,6 +1214,7 @@ if (is_cobalt) {
             "//third_party/blink/renderer/modules/cobalt/window_h_5_vcc.idl",
             "//third_party/blink/renderer/modules/cobalt/h5vcc_system/h_5_vcc_system.idl",
             "//third_party/blink/renderer/modules/cobalt/h5vcc_runtime/h_5_vcc_runtime.idl",
+            "//third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_extensions.idl",
           ],
           "abspath")
 }
@@ -1295,15 +1296,6 @@ if (target_os != "android") {
           "abspath")
 }
 
-# SourceBufferWriteHead
-# An extension to the SourceBuffer interface that allows web apps to check the
-# highest presentation timestamp written to the Renderer.
-if (is_cobalt && use_starboard_media) {
-  static_idl_files_in_modules += get_path_info(
-          [ "//third_party/blink/renderer/modules/mediasource/source_buffer_write_head.idl" ],
-          "abspath")
-}
-
 # Statically-defined (not runtime-generated) IDL files in 'modules' component.
 # These IDL definitions are used only for testing.
 static_idl_files_in_modules_for_testing = get_path_info(
diff --git a/third_party/blink/renderer/modules/cobalt/BUILD.gn b/third_party/blink/renderer/modules/cobalt/BUILD.gn
index 2f33ca3f117e..6f3c4df80432 100644
--- a/third_party/blink/renderer/modules/cobalt/BUILD.gn
+++ b/third_party/blink/renderer/modules/cobalt/BUILD.gn
@@ -23,5 +23,6 @@ blink_modules_sources("h_5_vcc") {
     "//third_party/blink/renderer/modules/cobalt/crash_annotator",
     "//third_party/blink/renderer/modules/cobalt/h5vcc_runtime",
     "//third_party/blink/renderer/modules/cobalt/h5vcc_system",
+    "//third_party/blink/renderer/modules/cobalt/mediasource",
   ]
 }
diff --git a/third_party/blink/renderer/modules/cobalt/mediasource/BUILD.gn b/third_party/blink/renderer/modules/cobalt/mediasource/BUILD.gn
new file mode 100644
index 000000000000..d03ee2694e41
--- /dev/null
+++ b/third_party/blink/renderer/modules/cobalt/mediasource/BUILD.gn
@@ -0,0 +1,24 @@
+# Copyright 2025 The Cobalt Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import("//third_party/blink/renderer/modules/modules.gni")
+
+blink_modules_sources("mediasource") {
+  sources = [
+    "source_buffer_write_head.cc",
+    "source_buffer_write_head.h",
+  ]
+
+  deps = [ "//third_party/blink/renderer/modules/mediasource:mediasource" ]
+}
diff --git a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.idl b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_extensions.idl
similarity index 99%
rename from third_party/blink/renderer/modules/mediasource/source_buffer_write_head.idl
rename to third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_extensions.idl
index 8ff5c972d000..cc70e323b348 100644
--- a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.idl
+++ b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_extensions.idl
@@ -21,4 +21,4 @@
     ImplementedAs=SourceBufferWriteHead
 ] partial interface SourceBuffer {
     [RaisesException] readonly attribute double writeHead;
-};
\ No newline at end of file
+};
diff --git a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.cc b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.cc
similarity index 92%
rename from third_party/blink/renderer/modules/mediasource/source_buffer_write_head.cc
rename to third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.cc
index 578ba3a42e0c..56ddc8d93a53 100644
--- a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.cc
+++ b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.cc
@@ -12,7 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#include "third_party/blink/renderer/modules/mediasource/source_buffer_write_head.h"
+#include "third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.h"
 
 #include "third_party/blink/renderer/modules/mediasource/source_buffer.h"
 #include "third_party/blink/renderer/platform/bindings/exception_state.h"
diff --git a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.h b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.h
similarity index 79%
rename from third_party/blink/renderer/modules/mediasource/source_buffer_write_head.h
rename to third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.h
index e5a52110d793..32b59d05edb0 100644
--- a/third_party/blink/renderer/modules/mediasource/source_buffer_write_head.h
+++ b/third_party/blink/renderer/modules/cobalt/mediasource/source_buffer_write_head.h
@@ -12,8 +12,8 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
-#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
-#define THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
+#ifndef THIRD_PARTY_BLINK_RENDERER_MODULES_COBALT_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
+#define THIRD_PARTY_BLINK_RENDERER_MODULES_COBALT_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
 
 #include "build/build_config.h"
 #include "third_party/blink/renderer/platform/wtf/allocator/allocator.h"
@@ -36,4 +36,4 @@ class SourceBufferWriteHead {
 
 }  // namespace blink
 
-#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
+#endif  // THIRD_PARTY_BLINK_RENDERER_MODULES_COBALT_MEDIASOURCE_SOURCE_BUFFER_WRITE_HEAD_H_
diff --git a/third_party/blink/renderer/modules/mediasource/BUILD.gn b/third_party/blink/renderer/modules/mediasource/BUILD.gn
index 0d8b68a606f5..c71a2071022a 100644
--- a/third_party/blink/renderer/modules/mediasource/BUILD.gn
+++ b/third_party/blink/renderer/modules/mediasource/BUILD.gn
@@ -56,10 +56,6 @@ blink_modules_sources("mediasource") {
     "//third_party/blink/renderer/modules/webcodecs:webcodecs",
   ]
   if (is_cobalt && use_starboard_media) {
-    sources += [
-      "source_buffer_write_head.cc",
-      "source_buffer_write_head.h",
-    ]
     deps += [ "//starboard($starboard_toolchain)" ]
   }
 }