public Builder setSpeakerBytes(com.google.protobuf.ByteString value) {
        if (value == null) {
          throw new NullPointerException();
        }
        checkByteStringIsUtf8(value);
        speaker_ = value;
        bitField0_ |= 0x00000001;
        onChanged();
        return this;
      }
<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>

@param value The bytes for speaker to set.
@return This builder for chaining.
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/MultiSpeakerMarkup.java