High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device.HDMI is a digital replacement for analog video standards.
The HDMI and DVI are both based on TMDS signal, the conversion between HDMI and DVI is without protocol conversion, it's bi-directional. Please pay attention, due to interface limit, the conversion is only HDMI-A to DVI-D single link, the maximum resolution is only up to 1080P@60Hz
The HDMI protocol is digital, the vga signal is analog, the conversion is a protocol conversion and it's also uni-directional.