Explicitly check that AudioGraph input is PCM 16

AudioGraph implicitly assumes that input will be PCM 16 bit, and not float.
Make the check explicit.

PiperOrigin-RevId: 616149131

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

@@ -57,7 +57,9 @@ import java.util.Objects;
 
   /** Returns whether an {@link AudioFormat} is valid as an input format. */
   public static boolean isInputAudioFormatValid(AudioFormat format) {
-    if (format.encoding == Format.NO_VALUE) {
+    // AudioGraphInput assumes PCM_16BIT -- see, for example, the automatic format conversions
+    // in AudioGraphInput.configureProcessing.
+    if (format.encoding != C.ENCODING_PCM_16BIT) {
       return false;
     }
     if (format.sampleRate == Format.NO_VALUE) {

libraries/transformer/src/test/java/androidx/media3/transformer/AudioGraphTest.java

@@ -48,6 +48,15 @@ public class AudioGraphTest {
   private static final AudioFormat SURROUND_50000 =
       new AudioFormat(/* sampleRate= */ 50_000, /* channelCount= */ 6, C.ENCODING_PCM_16BIT);
 
+  @Test
+  public void floatPcmFormat_isNotValidInputFormat() {
+    assertThat(
+            AudioGraph.isInputAudioFormatValid(
+                new AudioFormat(
+                    /* sampleRate= */ 44_100, /* channelCount= */ 1, C.ENCODING_PCM_FLOAT)))
+        .isFalse();
+  }
+
   @Test
   public void silentItem_outputsCorrectAmountOfBytes() throws Exception {
     AudioGraph audioGraph = new AudioGraph(new DefaultAudioMixer.Factory());