Add back VpxOutputBuffer proguard config.

This is needed to support old binary builds that still rely on the
existance of this class.

PiperOrigin-RevId: 344799495

extensions/vp9/proguard-rules.txt

@@ -9,3 +9,9 @@
 -keep class com.google.android.exoplayer2.video.VideoDecoderOutputBuffer {
 -keep class com.google.android.exoplayer2.video.VideoDecoderOutputBuffer {
     *;
     *;
 }
 }
+
+# The deprecated VpxOutputBuffer might be used by old binary versions. Remove
+# once VpxOutputBuffer is removed.
+-keep class com.google.android.exoplayer2.ext.vp9.VpxOutputBuffer {
+    *;
+}

extensions/vp9/src/main/java/com/google/android/exoplayer2/ext/vp9/VpxOutputBuffer.java

@@ -18,7 +18,8 @@ package com.google.android.exoplayer2.ext.vp9;
 import com.google.android.exoplayer2.video.VideoDecoderOutputBuffer;
 import com.google.android.exoplayer2.video.VideoDecoderOutputBuffer;
 
 
 // TODO(b/139174707): Delete this class once binaries in WVVp9OpusPlaybackTest are updated to depend
 // TODO(b/139174707): Delete this class once binaries in WVVp9OpusPlaybackTest are updated to depend
-// on VideoDecoderOutputBuffer. Also mark VideoDecoderOutputBuffer as final.
+// on VideoDecoderOutputBuffer. Also mark VideoDecoderOutputBuffer as final and remove proguard
+// config for VpxOutputBuffer.
 /**
 /**
  * Video output buffer, populated by {@link VpxDecoder}.
  * Video output buffer, populated by {@link VpxDecoder}.
  *
  *