@java.lang.Override
  public int getSerializedSize() {
    int size = memoizedSize;
    if (size != -1) return size;

    size = 0;
    if (inputSourceCase_ == 1) {
      size += com.google.protobuf.GeneratedMessageV3.computeStringSize(1, inputSource_);
    }
    if (inputSourceCase_ == 2) {
      size += com.google.protobuf.GeneratedMessageV3.computeStringSize(2, inputSource_);
    }
    if (((bitField0_ & 0x00000001) != 0)) {
      size +=
          com.google.protobuf.CodedOutputStream.computeMessageSize(3, getCustomPronunciations());
    }
    if (inputSourceCase_ == 4) {
      size +=
          com.google.protobuf.CodedOutputStream.computeMessageSize(
              4, (com.google.cloud.texttospeech.v1.MultiSpeakerMarkup) inputSource_);
    }
    if (inputSourceCase_ == 5) {
      size += com.google.protobuf.GeneratedMessageV3.computeStringSize(5, inputSource_);
    }
    size += getUnknownFields().getSerializedSize();
    memoizedSize = size;
    return size;
  }
<pre>
Optional. The pronunciation customizations are applied to the input. If
this is set, the input is synthesized using the given pronunciation
customizations.

The initial support is for en-us, with plans to expand to other locales in
the future. Instant Clone voices aren't supported.

In order to customize the pronunciation of a phrase, there must be an exact
match of the phrase in the input types. If using SSML, the phrase must not
be inside a phoneme tag.
</pre>

<code>
.google.cloud.texttospeech.v1.CustomPronunciations custom_pronunciations = 3 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-texttospeech/proto-google-cloud-texttospeech-v1/src/main/java/com/google/cloud/texttospeech/v1/SynthesisInput.java