public Builder setKey(java.lang.String value) {
      if (value == null) {
        throw new NullPointerException();
      }
      key_ = value;
      bitField0_ |= 0x00000001;
      onChanged();
      return this;
    }
<pre>
A unique key for this elementary stream. The key must be 1-63
characters in length. The key must begin and end with a letter (regardless
of case) or a number, but can contain dashes or underscores in between.
</pre>

<code>string key = 4;</code>

@param value The key to set.
@return This builder for chaining.
java-video-live-stream/proto-google-cloud-live-stream-v1/src/main/java/com/google/cloud/video/livestream/v1/ElementaryStream.java