MHL—What It Is and How to Use It

It extends the capabilities of HDMI

HDMI is the default wired audio/video connection protocol for home theaters. But, there's another way to extend its capabilities—MHL or Mobile High-Definition Link. What is it and how is it used? We explain below.

What Is MHL?

An MHL port lets you connect a smartphone, tablet, or another portable device to an HDTV, audio receiver, or video projector via either a special MHL-enabled HDMI input or an adapter.

HDMI combines high-resolution digital video (which includes 4K, 3D, and 8K depending on the version) and audio (up to eight channels) into a single connection, reducing the amount of cable clutter. It can send control signals between connected devices. This is referred to by several names depending on the manufacturer, but its generic name is HDMI-CEC.

Another HDMI feature is Audio Return Channel. This lets a single HDMI cable transfer audio signals in both directions between a compatible TV and home theater receiver or soundbar.

MHL uses the same physical end-connector HDMI uses, but it's not HDMI. It transmits HD video and audio from a connected device while charging that device at the same time. Certain smartphones and tablets support MHL, as do select TV sets.

hdmi-mhl-input-blu-ray-disc-player-example.jpg
MHL HDMI Input Example. Photo © Robert Silva - Licensed to About.com

MHL 1.0

MHL ver 1.0, introduced in June 2010, supports the transfer of up to 1080p high definition video and 7.1 channel PCM surround audio from the compatible portable device to a TV or home theater receiver, via a mini-HDMI connector on the portable device and a full-size HDMI connector on the home theater device that's MHL-enabled.

The MHL-enabled HDMI port also supplies power to your portable device (5 volts/500ma), so you don't have to use up battery power to watch a movie or listen to music.

When not using the MHL/HDMI port for connecting portable devices, you can still use it as a regular HDMI connection for your other home theater components, such as a Blu-ray Disc player.

Connecting MHL Smartphone to TV with MHL/HDMI Input
MHL Consortium

If you have an MHL-enabled smartphone or other device but your TV doesn't have an MHL-HDMI input, you can use a compatible adapter or dock to connect the two.

Connecting MHL Smartphone to TV with Standard HDMI Input Using Dock
MHL Consortium

MHL 2.0

Introduced in April 2012, it allows device charging from 4.5 watts at 900ma to 7.5 watts at 1.5 amps, and also adds 3D compatibility.

MHL 3.0

Released in August 2013, MHL 3.0 adds the following features:

  • 4K (Ultra HD/UHD) signal input supporting up to 30 fps (2160p/30).
  • 7.1 channel Dolby TrueHD and DTS-HD surround sound support.
  • Simultaneous High-Speed Data Channel accessibility.
  • Improved Remote Control Protocol (RCP) with support for external devices such as touch screens, keyboards, and mice.
  • Power and charging up to 10 Watts.
  • Compatibility with HDCP 2.2.
  • Multiple simultaneous display support (up to 4K monitors or TVs).
  • Backward compatibility with previous MHL 1.0 and 2.0 versions (including physical connections). However, devices with MHL versions 1.0 or 2.0 may not be able to access version 3.0 capabilities.

SuperMHL

Introduced in January 2015, superMHL supports 8K Ultra HD 120 Hz High Dynamic Range (HDR) video. It also supports object-based audio formats like Dolby Atmos and DTS:X. The Remote Control Protocol (RCP) was extended so multiple MHL-compatible devices can be linked and controlled via a single remote.

SuperMHL Connection (top) - USB 3.1 Type-C (bottom)
SuperMHL Connection (top) - USB 3.1 Type-C (bottom) - Not To Scale. Images provided by the MHL Consortium and Lattice Semiconductor

Here is what Super MHL connectivity provides:

  • 8K 120fps video pass-through capability.
  • Expanded 48-bit Deep Color and BT.2020 Color Gamut Support.
  • Support for High-Dynamic Range (HDR).
  • Support for advanced surround sound audio formats including Dolby Atmos®, DTS:X, and Auro 3D audio, as well as audio-only mode support.
  • Single remote control for multiple MHL devices (TV, AVR, Blu-ray player, STB).
  • Power charging up to 40W.
  • Multiple display capability from a single source.
  • Backward compatibility with MHL 1, 2 and 3.
  • Support for the MHL Alt Mode for the USB Type-C specifications.

Integrating MHL With USB

The MHL Consortium's version 3 connection protocol is also designed to integrate with the USB 3.1 framework via a USB Type-C connector. This is referred to as MHL Alt (Alternate) Mode.

This means the USB 3.1 Type-C connector is compatible with both USB and MHL functions.

MHL Alt Mode allows transfer up to 4K Ultra HD video resolution, multi-channel surround audio (including PCM, Dolby TrueHD, DTS-HD Master Audio), while also providing simultaneous MHL audio/video, USB Data, and power for connected portable devices when using a USB Type-C connector to compatible TVs, home theater receivers, and PCs equipped with a USB Type-C or full-size HDMI (via adapter) ports. MHL-enabled USB ports can use both USB or MHL functions.

One additional MHL Alt Mode feature is the Remote Control Protocol (RCP), which enables MHL sources plugged into compatible TVs to operate via the TV's remote control.

Products using the MHL Alt Mode include selected smartphones, tablets, and laptops equipped with USB 3.1 Type-C connectors.

MHL Alt Mode for USB Type-C
HDMI Consortium

To make adoption more flexible, cables are available that USB 3.1 Type-C connectors on one end, and HDMI, DVI, or VGA connectors on the other end. Docking products for compatible portable devices that include MHL Alt Mode compatible USB 3.1 Type-C, HDMI, DVI, or VGA connectors can also be used.

The decision to implement MHL Alt Mode on a specific product is determined by the product manufacturer. Just because a device might be equipped with a USB 3.1 Type-C connector, does not mean that it's automatically MHL Alt Mode-enabled.

If you desire that capability, look for the MHL designation next to the USB connector on either the source or destination device. If you're using the USB Type-C to HDMI connection option, make sure the HDMI connector on your destination device is labeled MHL compatible.

MHL Versions Comparison
MHL Feature Set MHL 1 MHL 2 MHL 3  superMHL
Maximum Resolution 1080p 1080p 4K/30 8K/120
HDR and BT2020 Color Gamut       X
Up to 8 (7.1) Audio Channels X X X X
Dolby TrueHD/DTS-HD Master Audio     X X
Dolby Atmos/DTS:X       X
MHL Control (RCP) X X X X
Power Charging 2.5 watts 7.5 watts 10 watts 40 watts
Copy Protection (HDCP) ver 1.4 ver 1.4 ver 2.2 ver 2.2
Multi-Display Support     up to 4 monitors or TVs up to 8 monitors or TVs
Connectors Adaptable Adaptable Adaptable super MHL proprietary, USB Type-C, Micro USB, HDMI Type A.

To dig deeper into the technical aspects of MHL technology, check out the official MHL Consortium website.