HDBaseT Part 1

HDBaseT 5Play: AV

HDBaseT is a bit-exact passthrough transmission line for AV.

In this lesson you'll learn about:

• Which video resolutions and audio formats are supported by HDBaseT,
• How supporting data including EDID, HDCP, and metadata is handled,
• HDBaseT 2.0 and 3.0 enhanced audio channels. 

HDBaseT is most commonly used to extend HDMI signals. When determining which AV formats can be supported, the simplest method is to reference the aggregate data rate through HDMI.

Since 2015, HDCP revision 2.2 included a dedicated specification for mapping HDCP to HDBaseT. This carries forward to HDCP 2.3.
HDBaseT also retains compatibility with previous versions of HDCP (e.g., HDCP 1.4).

• VESA Graphics Formats

HDBaseT equipment can also feature native HDBaseT ports, or interface other connections including DisplayPort, dual-link Digital Visual Interface (DVI), or USB-C. HDBaseT can also support many video resolutions beyond consumer video; namely, computer graphics resolutions, many of which are defined by the Video Electronics Standards Association (VESA).

An image generated by a graphics processing unit (GPU) is typically RGB color space and anything from 8 to 16 bits per channel (of 3 channels).

• The formula for calculating the raw data rate is:

"H-Resolution  x V-Resolution x bits per subpixel x 3 [color channels] x refresh rate"

• For example, the raw data rate WUXGA @ 10-bit 75Hz is calculated as follows:

1920 x 1200 x 10 [bits] x 3 [channels] x 75 [Hz] = 5.184 Gbps

• Compression

    As we saw previously, HDBaseT Spec 3.0 increases the native bandwidth of the link to 16Gbps, enabling up to 4K/60 with HDR or 4:4:4/RGB. But until products become available, interim solutions based on visually lossless compression (VLC) are proposed.

• Compressed Transmission Process

The compression technology approved by the HDBaseT Alliance applies VESA Display Stream Compression (DSC). This is a lightweight, extremely fast intra-frame compression codec, slicing the image line-by-line, or group of lines. The technology supports very low compression ratios, typically 2:1 to 3:1, but can range from 1.3:1 up to around 3.5:1.

• HDBaseT 3.0 + DSC

It is also conceivable that manufacturers may choose to combine DSC with HDBaseT 3.0 to achieve support for up to 4K/120 12-bit 4:4:4 HDR, or 8K/60 12-bit 4:2:0 HDR from an HDMI 2.1 or DisplayPort 2.0 source.

Applying simple mathematics, HDBaseT 3.0 (16Gbps) with DSC 3:1 ratio equates to 48Gbps (16 x 3), making it compatible with the upper uncompressed limit of HDMI 2.1.

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