public com.google.protobuf.ByteString getSpeakerBytes() {
        java.lang.Object ref = speaker_;
        if (ref instanceof String) {
          com.google.protobuf.ByteString b =
              com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
          speaker_ = b;
          return b;
        } else {
          return (com.google.protobuf.ByteString) ref;
        }
      }
<pre>
Required. The speaker of the turn, for example, 'O' or 'Q'. Please refer
to documentation for available speakers.
</pre>

<code>string speaker = 1 [(.google.api.field_behavior) = REQUIRED];</code>

@return The bytes for speaker.
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/MultiSpeakerMarkup.java