Make sure that VideoSamplePipeline is picked for image input

PiperOrigin-RevId: 511449658

library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/mh/ExportTest.java

@@ -253,4 +253,22 @@ public class ExportTest {
         .build()
         .run(testId, editedMediaItem);
   }
+
+  @Test
+  public void exportImage() throws Exception {
+    // TODO(b/262693274): consider removing this test when Robolectric tests have been added for
+    //  image input.
+    String testId = TAG + "_exportImage";
+    Context context = ApplicationProvider.getApplicationContext();
+    Transformer transformer = new Transformer.Builder(context).build();
+    String imageUri = "https://storage.googleapis.com/exoplayer-test-media-1/jpg/london.jpg";
+    EditedMediaItem editedMediaItem =
+        new EditedMediaItem.Builder(MediaItem.fromUri(imageUri))
+            .setDurationUs(1_000_000)
+            .setFrameRate(30)
+            .build();
+    new TransformerAndroidTestRunner.Builder(context, transformer)
+        .build()
+        .run(testId, editedMediaItem);
+  }
 }

library/transformer/src/main/java/com/google/android/exoplayer2/transformer/TransformerInternal.java

@@ -441,9 +441,7 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
               encoderFactory,
               muxerWrapper,
               fallbackListener);
-        }
-
-        if (MimeTypes.isVideo(firstInputFormat.sampleMimeType)) {
+        } else { // MIME type is video or image.
           return new VideoSamplePipeline(
               context,
               firstInputFormat,
@@ -459,7 +457,6 @@ import org.checkerframework.checker.nullness.qual.MonotonicNonNull;
               debugViewProvider);
         }
       }
-
       return new EncodedSamplePipeline(
           firstInputFormat,
           streamStartPositionUs,