A method and apparatus of video coding are disclosed. In the encoding side, video data are received, where a GDR (Gradual Decoding Refresh) picture type is supported by the encoding device. A syntax structure including a first syntax in NAL (Network Access Layer) unit header is generated, where an NAL unit type indicated by the first syntax comprises the GDR picture type. Encoded video data including the syntax structure from the video data are generated. A corresponding method and apparatus for the decoding side are also disclosed.