Since smartphones and tablets have virtually ceased to be inferior in capabilities to ordinary PCs, many users have rightly wanted to connect them to external displays, whether they are televisions or conventional monitors. You can do this for various purposes: for convenient surfing, if a full-fledged computer is not at hand, for showing presentations, or even for watching movies directly from your smartphone or even from an online service. However, a single standard has not yet been created for outputting and audio signals to TVs, so we decided to figure out how this can still be done and what is needed for this.
One of the first standards that made it possible to connect smartphones to a large screen was High Definition Multimedia Interface (HDMI) or HDMI. True, when HDMI just appeared in 2002, there was no talk of handheld devices: the standard was primarily intended for televisions and stationary media players.
Later, when smartphones and tablets became a mass product, the standard HDMI connector was reduced, resulting in two new types of connectors: mini-HDMI and micro-HDMI. They are fully compatible with the standard connector, and you can connect devices with miniature connectors to external displays using either special HDMI⇔mini-HDMI and HDMI⇔micro-HDMI cables, or a regular HDMI⇔HDMI cable with the desired adapter.
Several technology companies are developing the HDMI standard at once, including Philips, Hitachi and Sony. Interestingly, each manufacturer pays a consortium for each device with HDMI support 4 cents or 15 cents if the standard logo is not specified. In 2002, the first version of HDMI supported the transmission of Full HD at a frequency of 60 Hz, 8-channel audio with a frequency of 192 kHz (24 bits) and provided a maximum bandwidth of 4.9 Gbps. Since then, the capabilities of HDMI have continuously grown with the introduction of new specifications: the quality of transmitted and audio streams has improved, 3D support has appeared, and content protection has been introduced.
The latest HDMI specification, HDMI 2.0, which will soon become widely available, supports transmission in Ultra HD resolution (3840 × 2160 pixels) at a speed of 60 fps, or Full HD (1920×1080 pixels) in 3D format, while image output is possible in the new aspect ratio. 21: 9. The new version of the standard also allows you to transmit high-quality 24-channel sound with a sampling frequency of up to 1536 kHz. The total bandwidth of the HDMI 2.0 cable is up to 18 Gb / s.
Among the advantages of HDMI are the widespread and lack of need for external power when connecting devices, as well as a free micro-USB port to which you can connect peripherals. Perhaps the main disadvantage of HDMI in relation to smartphones is the need for a separate connector on the device’s body, which complicates the development of the gadget and increases its thickness. This flaw was corrected in the MHL standard, which is based on HDMI and was originally developed with an eye on mobile devices.
The consortium for the development of Mobile High-Definition Link (high-resolution mobile communication channel or MHL) included Toshiba and Sony, which participated in the design of HDMI, Samsung and Nokia joined them.
MHL combines the functionality of HDMI and micro-USB interfaces: you can transfer high-definition and sound via HDMI, and using the micro-USB standard, you can charge the device. The MHL 3.0 specification, adopted at the end of the summer of 2013, allows you to transmit in Ultra HD resolution with a frequency of 30 Hz, 7.1-channel audio with support for Dolby TrueHD and DTS-HD, as well as charge devices up to 10 watts. The first devices with support for MHL 3.0 were the Sony Xperia Z2 smartphone and the Sony Xperia Tablet Z2, presented at the MWC 2014 in Barcelona.
All MHL cables are usually divided into three types. The first and most common. a small adapter that has an HDMI input for connecting an HDMI cable from the TV, a micro-USB input for connecting external power (without this, the image output simply will not work) and a micro-USB output for connecting to the corresponding connector on the smartphone. This method is universal, but inconvenient in that it requires, in addition to the adapter itself, two more cables.
This drawback is designed to eliminate a new type of MHL cables that can directly connect the HDMI output of the TV and the MHL output of the smartphone. The smartphone’s battery is charged directly via an HDMI cable, and the device does not require external power, but not all TV models support this feature so far.
The third type of MHL cables is Samsung’s exclusive development, they can be found both as separate adapters and as part of other accessories, for example, docking stations. The main difference from the standard MHL connectors is the use of additional contacts. 11 pins in the connector against the standard 5 micro-USB pins. Such a solution allows Samsung to expand the functionality of the MHL standard (for example, it becomes possible to connect peripheral devices), but makes 5-pin connectors with 11-pin devices incompatible without special adapters, as well as vice versa, 11-pin cables with all other smartphones.
The main advantage of the combined MHL connector compared to the “classic” HDMI is the lack of the need to use two connectors at once in mobile devices, as well as the ability to simultaneously charge the smartphone. Of the minuses, it is possible to simultaneously use a USB host and MHL, which makes it impossible to connect to a gadget, for example, an external drive for watching movies. Samsung devices and accessories, which implement the functionality of a USB host via MHL, are deprived of this drawback, but this standard is incompatible with other MHL devices.
The closest competing standard to MHL is Analogix’s SlimPort, which in turn is based on DisplayPort technology developed by VESA.
SlimPort features are very close to MHL specifications: 4K and 8-channel audio are supported. By its principle of operation, SlimPort is also practically indistinguishable from MHL: a micro-USB connector is used as an input on the smartphone, and a special adapter similar to that used with MHL will be required to connect a monitor or TV with DisplayPort or HDMI support.
There is also a SlimPort adapter from micro-USB to VGA, but this is rather exotic, although it may come in handy for someone.
Despite so many similarities, there is still a difference between the standards. Firstly, SlimPort does not require external power for smartphones. Secondly, through SlimPort, the USB host function was initially implemented. the corresponding devices can be connected directly to the SlimPort-HDMI adapter. Well, and thirdly, SlimPort, like DisplayPort, unlike HDMI, is free of any patent payments.
It is important to note that SlimPort is not compatible with MHL (despite using the same micro-USB connector) and is less common. At the moment, this standard is used in the latest devices of the Nexus line, including Nexus 4, Nexus 5 and Nexus 7 (2013), as well as some chromebooks.
All the standards described before this one way or another implied the physical connection of the smartphone to the TV, but now many manufacturers are trying to get rid of the wires between the devices. One of the most common ways that this can be done is the Miracast standard developed by the Wi-Fi alliance and based on Wi-Fi Direct technology, which appeared relatively recently, in 2012.
Miracast does not require any additional transmitters in mobile devices, except for the already built-in Wi-Fi module, and interaction with the TV can be carried out both through the built-in Wi-Fi, and through an external dongle connected to the HDMI connector. The Miracast standard has a high speed, supports transmission in resolutions up to 1920×1200 pixels (there is currently no possibility to transmit 4K images) and Dolby AC3 5.1-channel audio.
Of course, the characteristics of Miracast are noticeably weaker than that of MHL or SlimPort. But this can not be called a significant drawback: today, few people may need to output to the TV a better image than this standard allows. The main obstacle to using Miracast may be the incompatibility of its implementations in different models of smartphones, TVs and dongles. Given that at the moment the Miracast standard is not even two years old, we can hope that in the near future it will catch up with wired competitors in terms of performance and become universal.
Wireless Display technology or, in short, WiDi, developed by Intel, is an alternative to Miracast and is compatible with WiDi 3.5. The characteristics of the transmitted and audio streams are also very close to Miracast: the maximum resolution is 1080p and 5.1-channel surround sound.
AirPlay is a proprietary technology that was developed by Apple only for its own devices that can serve as content transmitters. You can receive and play content either through the Apple TV set-top box, or using one of the many compatible devices (among which there are media players, and music centers, and many other gadgets) that Apple itself certifies. No additional configuration on the part of the user is required. it is enough that both devices are on the same local network.
Initially, the AirPlay protocol allowed only transferring and audio files from the corresponding applications to the iPhone or iPod, but with the introduction of AirPlay Mirorring technology, which first appeared on the iPad 2 and iPhone 4S, it became possible to display on the big screen a direct picture from the display of a smartphone or tablet. This, for example, allows you to play on a large display, show presentations, work with documents and perform many other previously inaccessible actions.
Mirrorlink and CarPlay
In the list of mentioned technologies, Mirrorlink and CarPlay protocols stand apart. Although they are used to connect smartphones to external displays, they are not intended for use with a TV at home or at work, but for communication with the car’s on-board system.
Mirrorlink is a public standard that can be used by smartphone manufacturers on any platform. Connecting to the car is carried out using a USB cable, and on-board computer screen can display both a simple image from the smartphone’s display and applications optimized for use in the car.
CarPlay works in a similar way, except that this technology, like AirPlay, is strictly proprietary and is available only for Apple mobile devices running iOS. When you connect your iPhone or other compatible device to the car, a number of adapted applications become available, including phone, cards, messages, and music. Programs can be controlled in several ways, depending on whether the car manufacturer provided for them. using the touch screen of the on-board computer, using the buttons on the steering wheel and dashboard, or by voice using Siri.
The appearance on the market of a large number of cars with Mirrorlink and Carplay support is expected in the second half of 2014, and in the future more and more car makers intend to implement support for these protocols.
As part of this material, we cannot consider all methods of outputting images from the screen of a smartphone to a TV or external monitor. For example, there are various applications that allow you to duplicate the screen of a handheld device on a monitor connected to a PC. Nevertheless, we tried to talk about the most common and universal methods, the knowledge of which will be useful if you need to show a presentation on a large screen or just watch a movie directly from your smartphone. We hope that the article helped to understand the interweaving of different standards and their sometimes incompatible specifications: each of the described methods has a number of its pros and cons, therefore, we advise you to choose the one that is most convenient and affordable for you.