MHL - What It Is and How It Impacts Home Theater

MHL Logo
MHL Logo. MHL Consortium

With the advent of HDMI as the default wired audio/video connection protocol for home theater, new ways to take advantage of its capabilities are always being looked at.

At first, HDMI was a way to combine both high-resolution digital video (which also now includes 4K and 3D) and audio (up 8 channels) into a single connection, reducing the amount of cable clutter.

Next came the idea of using HDMI as a way to send control signals between connected devices, without having to utilize a separate control system.

This is referred to by several names depending on the manufacturer (Sony Bravia Link, Panasonic Viera Link, Sharp Aquos Link, Samsung Anynet+, etc...), but its generic name is HDMI-CEC.

Another idea that is now being implemented successfully is Audio Return Channel, which enables a single HDMI cable to transfer audio signals in both directions, between a compatible TV and Home Theater Receiver, eliminating the need to make a separate audio connection from the TV to a home theater receiver.

Enter MHL

Another feature that extends HDMI capabilities further is MHL or Mobile High-Definition Link.

To put it simply, MHL allows a new generation of portable devices, such as smartphones and tablets to connect to your TV or home theater receiver, via HDMI.

MHL ver 1.0 enables users to transfer 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 is MHL-enabled.

The MHL-enabled HDMI port also supplies power to your portable device (5 volts/500ma), so you don't have to worry about using up battery power to watch a movie or listen to music. Also, when not using the MHL/HDMI port for connecting portable devices, you can still use it a regular HDMI connection for your other home theater components, such as a Blu-ray Disc player.

MHL and Smart TV

However, it doesn't stop there. MHL also has implications for Smart TV capabilities. For example, when you buy a Smart TV, it comes with a certain level of media streaming and/or network functionality, and, although new services and features can be added, there is a limitation as to how much upgrading can be accomplished without having to buy a new TV to get more capabilities. Of course, you could connect an additional media streamer, but that means another box connected to your TV and more connection cables.

One application of MHL is illustrated by Roku, which, a few years back, took its media streamer platform, reduced it down to about the size of the USB Flash Drive, but instead of USB, incorporated an MHL-enabled HDMI connector that can plug into a TV that has an MHL-enabled HDMI input.

This "Streaming Stick", as Roku, refers to it, comes with its own built-in Wifi connection interface, so you don't need one on the TV to connect your home network and the internet to access TV and movie streaming content - and you don't need a separate box and more cables either.

Although most plug-in streaming stick devices, no longer require HDMI inputs that are MHL compatible - one advantage MHL provides is direct access to power without the need to make a separate power connection via USB or AC power adapter.

MHL 3.0

On August 20, 2013, additional upgrades were announced for MHL, which is labeled MHL 3.0. The added capabilities include:

  • 4K (Ultra HD/UHD) signal input support 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.
  • Backward compatible 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.

    Integrating MHL With USB

    The MHL Consortium has announced that its version 3 connection protocol, can also be integrated into the USB 3.1 framework via a USB Type-C connector. The MHL Consortium refers to this application as MHL Alt (Alternate) Mode (in other words, 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 will be able to be used for both USB or MHL functions.

    One additional MHL Alt Mode feature is Remote Control Protocol (RCP) - which enables HML sources plugged into compatible TVs to be operated 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.

    Also, 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, allowing connection with more devices. In addition, see docking products for compatible portable devices that include MHL Alt Mode compatible USB 3.1 Type-C, HDMI, DVI, or VGA connectors as needed.

    However, the decision to implement MHL Alt Mode on a specific product is determined by the product manufacturer. In other words, just because a device might be equipped with a USB 3.1 Type-C connector, does not mean that it is automatically MHL Alt Mode-enabled. If you desire that capability is sure to look for the MHL designation next to the USB connector on either the source or destination device. Also, if you are using the USB Type-C to HDMI connection option, make sure that the HDMI connector on your destination device is labeled as being MHL compatible.

    Super MHL

    Keeping an eye out towards the future, the MHL Consortium has taken MHL application further with the introduction of Super MHL.

    Super MHL is designed to extend MHL capability into the forthcoming 8K infrastructure.

    It will be a while before 8K reaches the home, and there is no 8K content or broadcasting/streaming infrastructure in place yet. Also, with 4K TV broadcasting just now getting off the ground (won't be fully realized until about 2020) current 4K Ultra HD TVs and products will hold their ground for some time.

    However, to prepare for the eventuality of 8K, new connectivity solutions will be required to deliver an acceptable 8K viewing experience.

    This is where Super MHL comes in.

    Here is what Super MHL connectivity provides:

    The Bottom Line

    HDMI is the dominant form of connectivity for TVs and home theater components - but, by itself, isn't compatible with everything.MHL provides a bridge that allows connection integration of portable devices with TVs and home theater components, as well as the ability to integrate portable devices with PCs and Laptops via compatibility with USB 3.1 using the type C interface. In addition, MHL also has implications for the future of 8K connectivity.

    Stay Tuned as updates come in.

    To dig deeper into the technical aspects of MHL technology - check out The Official MHL Consortium Website