How Many TMDS Channels Are in HDMI 1.4?

An HDMI 1.4 connection uses four Transition-Minimized Differential Signaling (TMDS) channels in total to transmit signals between a source and a display. Three of these channels are dedicated data channels responsible for carrying uncompressed video, audio, and auxiliary information, while the fourth channel serves as a dedicated differential clock line. Together, this four-channel architecture provides the 10.2 Gbps aggregate bandwidth that allows HDMI 1.4 to support 1080p high refresh rates, 3D content, and 4K resolution at 30 Hz.

The Architecture of HDMI 1.4 Transmission

HDMI relies on TMDS technology to convert parallel digital data into a high-speed, serial differential stream resistant to electromagnetic interference. In an HDMI 1.4 physical interface, these signals run across four shielded twisted pairs:

• TMDS Data Channel 0: Primarily carries the Blue color component, along with horizontal and vertical synchronization signals (HSYNC and VSYNC) and packetized audio/auxiliary data during blanking intervals.
• TMDS Data Channel 1: Primarily carries the Green color component alongside audio and auxiliary control packets.
• TMDS Data Channel 2: Primarily carries the Red color component alongside audio and auxiliary control packets.
• TMDS Clock Channel: Carries a dedicated differential clock signal that runs at the character rate, allowing the receiving device to synchronize and reconstruct the incoming data on Channels 0 through 2.

How Audiovisual Data Shares the Channels

Unlike older analog connections where video and audio ran on completely isolated physical lines, HDMI multiplexes audio and auxiliary metadata directly into the video data stream.

During the active video periods of each frame, Data Channels 0, 1, and 2 transmit pixel data corresponding to RGB or YCbCr color spaces. During the horizontal and vertical blanking intervals—periods when the display is not actively drawing pixels—the interface switches into Data Island Mode. In this mode, multi-channel digital audio (such as uncompressed LPCM, Dolby TrueHD, or DTS-HD Master Audio) and auxiliary metadata packets are interleaved across those same three data channels.

Bandwidth and Throughput Limits

In HDMI 1.4, each of the three TMDS data channels operates at a maximum single-link character rate of 340 MHz. Because TMDS utilizes 10-bit encoding per 8-bit character, each data channel supports a throughput of up to 3.4 Gbps.

Combining the three data channels yields a total theoretical transmission rate of 10.2 Gbps. Factoring out encoding overhead, the effective maximum data rate for payload delivery across the connection is 8.16 Gbps. The clock channel does not carry payload data, meaning the entirety of the audio and visual throughput relies exclusively on the three active TMDS data links.