/eɪtʃ diː aɪ ɛm aɪ/
n. "Proprietary audio/video interface carrying TMDS streams with CEC unlike royalty-free DisplayPort."
HDMI, short for High-Definition Multimedia Interface, transmits uncompressed video, multi-channel audio, and control data over TMDS lanes (HDMI2.1=48Gbps), supporting 10K@120Hz with DSC, ARC/eARC return audio, and CEC device control across Type-A/D/Mini/Micro connectors. Unlike DVI's video-only limitation, HDMI embeds DD++/EDID, Consumer Electronics Control (CEC=BraviaSync), and Audio Return Channel (ARC) in blanking intervals, with licensing fees funding HDMI Forum evolution contrasting VESA's open DisplayPort.
Key characteristics of HDMI include: TMDS Encoding 8b→10b like DVI but with audio/infoframes (HDMI2.1=12/24Gbps TMDS x3 lanes); HDR10/HLG/Dolby Vision dynamic metadata; eARC bidirectional 37Mbps uncompressed audio (Dolby TrueHD); Variable Refresh Rate (VRR=FreeSync); Source-Based Tone Mapping for mismatched dynamic range; Ultra High Speed cables mandatory for 48Gbps (48Gbps active optical).
Conceptual example of HDMI usage:
/* HDMI 2.1 Source InfoFrame packet for 4K@120Hz HDR */
struct hdmi_infoframe {
uint8_t type = 0x87; // AVI InfoFrame
uint8_t version = 0x02;
uint8_t length = 0x0D;
uint8_t checksum;
// Video ID Code (VIC) for 4K120
uint8_t vic = 97; // 3840x2160@120Hz
uint8_t pixel_repeat = 0;
// Colorimetry + Dynamic Range
uint8_t colorimetry = 0x04; // BT.2020
uint8_t dynamic_range = 0x01; // HDR Static Metadata Type 1
} avi_if;
void hdmi_send_infoframe(struct hdmi_infoframe *ifp) {
calculate_checksum(ifp);
tmds_insert_during_blanking(ifp, HDMI_PACKET_PERIOD);
}Conceptually, HDMI bundles pixel clock+TMDS data lanes with sideband packets during blanking (like DisplayPort MSA but HDMI-licensed), tunneling through USB4 ALT mode while CEC chains Blu-ray→soundbar→TV control. HDMI2.1 FRL (Fixed Rate Link) replaces TMDS for 48Gbps, stress-tested via PRBS patterns hitting receiver CTLE/DFE, with Ultra High Speed cables ensuring 1e-12 BER unlike passive copper limits plaguing early HDMI2.0 18Gbps deployments.