Disable fallback in tests that don't test fallback.

Fallback is only disabled for robolectric and instrumentation tests.
For MH tests, fallback is not disabled, as it may be needed due to
the broad range of devices available.

PiperOrigin-RevId: 426403167

library/transformer/src/androidTest/java/com/google/android/exoplayer2/transformer/TransformerEndToEndTest.java

@@ -47,6 +47,8 @@ public class TransformerEndToEndTest {
             .setTransformationRequest(
                 new TransformationRequest.Builder().setVideoMimeType(MimeTypes.VIDEO_H264).build())
             .setMuxerFactory(muxerFactory)
+            .setEncoderFactory(
+                new DefaultEncoderFactory(EncoderSelector.DEFAULT, /* disableFallback= */ true))
             .build();
     // Result of the following command:
     // ffprobe -count_frames -select_streams v:0 -show_entries stream=nb_read_frames bear-vp9.webm
@@ -78,6 +80,8 @@ public class TransformerEndToEndTest {
                     .setTransformationMatrix(transformationMatrix)
                     .build())
             .setMuxerFactory(muxerFactory)
+            .setEncoderFactory(
+                new DefaultEncoderFactory(EncoderSelector.DEFAULT, /* disableFallback= */ true))
             .build();
     // Result of the following command:
     // ffprobe -count_frames -select_streams v:0 -show_entries stream=nb_read_frames sample.mp4

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

@@ -73,9 +73,18 @@ public final class DefaultEncoderFactory implements Codec.EncoderFactory {
     // TODO(b/210591626) Add encoder selection for audio.
     checkArgument(!allowedMimeTypes.isEmpty());
     if (!allowedMimeTypes.contains(format.sampleMimeType)) {
-      // TODO(b/210591626): Pick fallback MIME type using same strategy as for encoder
-      // capabilities limitations.
-      format = format.buildUpon().setSampleMimeType(allowedMimeTypes.get(0)).build();
+      if (!disableFallback) {
+        // TODO(b/210591626): Pick fallback MIME type using same strategy as for encoder
+        // capabilities limitations.
+        format = format.buildUpon().setSampleMimeType(allowedMimeTypes.get(0)).build();
+      } else {
+        throw createTransformationException(
+            new IllegalArgumentException("The requested output format is not supported."),
+            format,
+            /* isVideo= */ false,
+            /* isDecoder= */ false,
+            /* mediaCodecName= */ null);
+      }
     }
     MediaFormat mediaFormat =
         MediaFormat.createAudioFormat(
@@ -110,8 +119,7 @@ public final class DefaultEncoderFactory implements Codec.EncoderFactory {
             format, videoEncoderSelector, allowedMimeTypes, disableFallback);
     if (encoderAndClosestFormatSupport == null) {
       throw createTransformationException(
-          new IllegalArgumentException(
-              "No encoder available that supports the requested output format."),
+          new IllegalArgumentException("The requested output format is not supported."),
           format,
           /* isVideo= */ true,
           /* isDecoder= */ false,