diff --git a/extensions/av1/README.md b/extensions/av1/README.md
index b57f0b484c..276daae4e2 100644
--- a/extensions/av1/README.md
+++ b/extensions/av1/README.md
@@ -11,7 +11,7 @@ more external libraries as described below. These are licensed separately.
 
 [Apache 2.0]: https://github.com/google/ExoPlayer/blob/release-v2/LICENSE
 
-## Build instructions ##
+## Build instructions (Linux, macOS) ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
@@ -61,6 +61,13 @@ to configure and build libgav1 and the extension's [JNI wrapper library][].
 [Ninja]: https://ninja-build.org
 [JNI wrapper library]: https://github.com/google/ExoPlayer/blob/release-v2/extensions/av1/src/main/jni/gav1_jni.cc
 
+## Build instructions (Windows) ##
+
+We do not provide support for building this extension on Windows, however it
+should be possible to follow the Linux instructions in [Windows PowerShell][].
+
+[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell
+
 ## Using the extension ##
 
 Once you've followed the instructions above to check out, build and depend on
diff --git a/extensions/ffmpeg/README.md b/extensions/ffmpeg/README.md
index f8120ed11b..fe4aca772a 100644
--- a/extensions/ffmpeg/README.md
+++ b/extensions/ffmpeg/README.md
@@ -11,7 +11,7 @@ more external libraries as described below. These are licensed separately.
 
 [Apache 2.0]: https://github.com/google/ExoPlayer/blob/release-v2/LICENSE
 
-## Build instructions ##
+## Build instructions (Linux, macOS) ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
@@ -66,6 +66,13 @@ cd "${FFMPEG_EXT_PATH}" && \
 ${NDK_PATH}/ndk-build APP_ABI="armeabi-v7a arm64-v8a x86" -j4
 ```
 
+## Build instructions (Windows) ##
+
+We do not provide support for building this extension on Windows, however it
+should be possible to follow the Linux instructions in [Windows PowerShell][].
+
+[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell
+
 ## Using the extension ##
 
 Once you've followed the instructions above to check out, build and depend on
diff --git a/extensions/flac/README.md b/extensions/flac/README.md
index e534f9b2ac..84a92f9586 100644
--- a/extensions/flac/README.md
+++ b/extensions/flac/README.md
@@ -11,7 +11,7 @@ more external libraries as described below. These are licensed separately.
 
 [Apache 2.0]: https://github.com/google/ExoPlayer/blob/release-v2/LICENSE
 
-## Build instructions ##
+## Build instructions (Linux, macOS) ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
@@ -53,6 +53,13 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
 [top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
 [Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
 
+## Build instructions (Windows) ##
+
+We do not provide support for building this extension on Windows, however it
+should be possible to follow the Linux instructions in [Windows PowerShell][].
+
+[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell
+
 ## Using the extension ##
 
 Once you've followed the instructions above to check out, build and depend on
diff --git a/extensions/opus/README.md b/extensions/opus/README.md
index ce88f0ef7d..05448f2073 100644
--- a/extensions/opus/README.md
+++ b/extensions/opus/README.md
@@ -11,7 +11,7 @@ more external libraries as described below. These are licensed separately.
 
 [Apache 2.0]: https://github.com/google/ExoPlayer/blob/release-v2/LICENSE
 
-## Build instructions ##
+## Build instructions (Linux, macOS) ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
@@ -58,6 +58,13 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
 [top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
 [Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
 
+## Build instructions (Windows) ##
+
+We do not provide support for building this extension on Windows, however it
+should be possible to follow the Linux instructions in [Windows PowerShell][].
+
+[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell
+
 ## Notes ##
 
 * Every time there is a change to the libopus checkout:
diff --git a/extensions/vp9/README.md b/extensions/vp9/README.md
index 03d9b7413d..71241d9a4f 100644
--- a/extensions/vp9/README.md
+++ b/extensions/vp9/README.md
@@ -11,7 +11,7 @@ more external libraries as described below. These are licensed separately.
 
 [Apache 2.0]: https://github.com/google/ExoPlayer/blob/release-v2/LICENSE
 
-## Build instructions ##
+## Build instructions (Linux, macOS) ##
 
 To use this extension you need to clone the ExoPlayer repository and depend on
 its modules locally. Instructions for doing this can be found in ExoPlayer's
@@ -68,6 +68,13 @@ ${NDK_PATH}/ndk-build APP_ABI=all -j4
 [top level README]: https://github.com/google/ExoPlayer/blob/release-v2/README.md
 [Android NDK]: https://developer.android.com/tools/sdk/ndk/index.html
 
+## Build instructions (Windows) ##
+
+We do not provide support for building this extension on Windows, however it
+should be possible to follow the Linux instructions in [Windows PowerShell][].
+
+[Windows PowerShell]: https://docs.microsoft.com/en-us/powershell/scripting/getting-started/getting-started-with-windows-powershell
+
 ## Notes ##
 
 * Every time there is a change to the libvpx checkout: