Force signal encoder end of stream after all output has been processed

Fixes a rare failure on some devices.
Only available when `experimentalSetMaxFramesInEncoder` is enabled.

PiperOrigin-RevId: 723498652

libraries/transformer/src/androidTest/java/androidx/media3/transformer/ParameterizedInputSequenceExportTest.java

@@ -110,6 +110,7 @@ public final class ParameterizedInputSequenceExportTest {
     assumeSequenceFormatsSupported(context, testId, sequence);
     Transformer transformer =
         new Transformer.Builder(context)
+            .experimentalSetMaxFramesInEncoder(16)
             .setEncoderFactory(
                 new DefaultEncoderFactory.Builder(context).setEnableFallback(false).build())
             .build();
@@ -131,6 +132,7 @@ public final class ParameterizedInputSequenceExportTest {
     assumeSequenceFormatsSupported(context, testId, sequence);
     Transformer transformer =
         new Transformer.Builder(context)
+            .experimentalSetMaxFramesInEncoder(16)
             .setEncoderFactory(
                 new DefaultEncoderFactory.Builder(context).setEnableFallback(false).build())
             .build();

libraries/transformer/src/main/java/androidx/media3/transformer/VideoSampleExporter.java

@@ -214,7 +214,10 @@ import org.checkerframework.dataflow.qual.Pure;
 
   @Override
   protected boolean isMuxerInputEnded() {
-    return encoderWrapper.isEnded();
+    // Sometimes the encoder fails to produce an output buffer with end of stream flag after
+    // end of stream is signalled. See b/365484741.
+    // Treat empty encoder (no frames in progress) as if it has ended.
+    return encoderWrapper.isEnded() || videoGraph.hasEncoderReleasedAllBuffersAfterEndOfStream();
   }
 
   /**
@@ -582,6 +585,18 @@ import org.checkerframework.dataflow.qual.Pure;
       videoGraph.release();
     }
 
+    public boolean hasEncoderReleasedAllBuffersAfterEndOfStream() {
+      if (renderFramesAutomatically) {
+        // Video graph wrapper does not track encoder buffers.
+        return false;
+      }
+      boolean isEndOfStreamSeen =
+          (VideoSampleExporter.this.finalFramePresentationTimeUs != C.TIME_UNSET);
+      synchronized (lock) {
+        return framesInEncoder == 0 && isEndOfStreamSeen;
+      }
+    }
+
     public void onEncoderBufferReleased() {
       if (!renderFramesAutomatically) {
         synchronized (lock) {