A:Answer Hi TonyM. The HDMI ARC on the LG SL5Y 2.1 Channel 400W Sound Bar w/ DTS Virtual: X & High Resolution Audio is an HDMI 1.4 port and it is HDCP compliant. To pass a 4K signal, the HDMI ports would need to be HDMI 2.0 ports & HDCP 2.2 compliant. HDMI ARC is based on the IEC 60958-1 specification, which is basically S/PDIF that is also used as the foundation for optical audio. The flexibility of the HDMI standard (plus copy protection), however, allows additional audio formats to be transmitted over HDMI ARC than via optical but bandwidth is still very limited at 1Mb/s at the base level, although it can be pushed to pass more data. The limited bandwidth allows HDMI ARC to deliver stereo audio and compressed 5.1 surround. It can be pushed to transmit Dolby Atmos streams containing metadata but it requires an extension called Common mode that is not part of the base specification and must be actively supported in both TV (i.e. LG OLED) and receiver. However, bandwidth of standard HDMI ARC is too limited for compressed 7.1 surround and even more so for lossless audio (Dolby TrueHD or DTS-HD MA). Lip sync correction is also optional under ARC...^IFV
