It's easy to take for granted how conveniently plug-and-play so many of our devices are, these days. Apple's Thunderbolt connector, for example, incorporated the DisplayPort video standard, making it easy to plug DisplayPort cables into Thunderbolt-equipped MacBooks through the same port. And millions of Android phones, which almost universally charge off of micro USB ports, can output video over MHL, or Mobile High Definition Link.
But MHL isn't the only video standard that can output via a microUSB port; in 2012, Google introduced the Nexus 4 and the Nexus 7 with a competing standard called Slimport. The two are essentially competing to be the most convenient. MHL has an install base of millions, and outputs to the ubiquitous HDMI standard. But SlimPort offers something just a bit different: DisplayPort compatibility, which means it can easily output to a variety of video standards.
The MHL consortium announced a 3.0 spec on Tuesday, upping Mobile High Link's resolution support from 1080p up to 4K at 30 frames per second. Future Android phones and other devices that support the new spec will be able to push video at 3840x2160 while drawing up to 10 watts of charging power; they'll also support 7.1 surround sound audio and the HDCP 2.2 content protection standard. Of course, the 3.0 spec is mostly futureproofing, since 4K TVs are just beginning to show up in stores and homes.
MHL has found its way into more than 200 products at this point, with millions of devices on the market. SlimPort, by comparison, is available in only a few: Google's Nexus 4 and Nexus 7, the LG Optimus G Pro, a Fujitsu Windows 8 tablet and the ASUS PadFone Infinity. Last year Anandtech did a good job of summarizing what makes SlimPort different from MHL:
"SlimPort is a new video output standard which works over microUSB, and is effectively an MHL alternative based on the DisplayPort standard administered by VESA. SlimPort is offered both license and royalty free, and supports up to 1080p60 or 1080p30 with 3D content over HDMI 1.4 (up to 5.4 Gbps of bandwidth), in addition to support for DVI, VGA (up to 1366x768 and 720p at 60 Hz), and DisplayPort.
What's different about SlimPort from a user-facing perspective is that external microUSB power is not required for the adapter to work and is instead only required for optional charging. At the same time, the adapters draw no power from the source to operate."
SlimPort's support for the DisplayPort standard--specifically Mobility DisplayPort--means it can output video at the same 4K resolution as MHL, though not via HDMI (yet, anyway). And here SlimPort hasn't really made good on its potential, yet; though it's based on the flexible DisplayPort standard, the only SlimPort adapters currently available are for VGA and HDMI connectors. The upshot is that you won't be plugging a Nexus 7 into a 1440p DisplayPort computer monitor anytime soon.
Since DisplayPort can pass along an HDMI signal, SlimPort more or less works like MHL right now. Both output from a phone's microUSB port and plug into a TV's HDMI port. Both will support 1080p60 video. Next year, as the MHL 3.0 spec comes into play, the two may begin to diverge more noticeably--it'll especially be interesting to see if any more Android devices follow Google's lead in backing the SlimPort standard.