When encoding a 4K source, be sure to use a high speed HDMI cable (usually labeled as "High Speed HDMI Cable").
Before streaming using a 4K source, be sure to verify that your destination supports 4K.
HEVC
RTMP and RTSP output protocols do not support HEVC. To stream HEVC, set up a multicast, unicast, SRT, or HTTP stream. HEVC can also be recorded or uploaded to an FTP server.
Before streaming HEVC, verify that it is supported by the receiver.