Use symlinking for dependency on libvpx

As opposed to in-source git-clone.

PiperOrigin-RevId: 344525899

extensions/vp9/README.md

@@ -35,25 +35,23 @@ VP9_EXT_PATH="${EXOPLAYER_ROOT}/extensions/vp9/src/main"
 NDK_PATH="<path to Android NDK>"
 NDK_PATH="<path to Android NDK>"
 ```
 ```
 
 
-* Fetch libvpx:
-
-```
-cd "${VP9_EXT_PATH}/jni" && \
-git clone https://chromium.googlesource.com/webm/libvpx libvpx
-```
-
-* Checkout an appropriate branch of libvpx. We cannot guarantee compatibility
+* Fetch an appropriate branch of libvpx. We cannot guarantee compatibility
   with all versions of libvpx. We currently recommend version 1.8.0:
   with all versions of libvpx. We currently recommend version 1.8.0:
 
 
 ```
 ```
-cd "${VP9_EXT_PATH}/jni/libvpx" && \
-git checkout tags/v1.8.0 -b v1.8.0
+cd "<preferred location for libvpx>" && \
+git clone https://chromium.googlesource.com/webm/libvpx && \
+cd libvpx && \
+git checkout tags/v1.8.0 -b v1.8.0 && \
+LIBVPX_PATH="$(pwd)"
 ```
 ```
 
 
-* Run a script that generates necessary configuration files for libvpx:
+* Add a link to the libvpx source code in the vp9 extension `jni` directory and
+  run a script that generates necessary configuration files for libvpx:
 
 
 ```
 ```
 cd ${VP9_EXT_PATH}/jni && \
 cd ${VP9_EXT_PATH}/jni && \
+ln -s "$LIBVPX_PATH" libvpx && \
 ./generate_libvpx_android_configs.sh
 ./generate_libvpx_android_configs.sh
 ```
 ```
 
 
@@ -80,8 +78,8 @@ should be possible to follow the Linux instructions in [Windows PowerShell][].
   * Android config scripts should be re-generated by running
   * Android config scripts should be re-generated by running
     `generate_libvpx_android_configs.sh`
     `generate_libvpx_android_configs.sh`
   * Clean and re-build the project.
   * Clean and re-build the project.
-* If you want to use your own version of libvpx, place it in
-  `${VP9_EXT_PATH}/jni/libvpx`. Please note that
+* If you want to use your own version of libvpx, refer to it using the a symlink
+  in `${VP9_EXT_PATH}/jni/libvpx`. Please note that
   `generate_libvpx_android_configs.sh` and the makefiles may need to be modified
   `generate_libvpx_android_configs.sh` and the makefiles may need to be modified
   to work with arbitrary versions of libvpx.
   to work with arbitrary versions of libvpx.