Streaming the Screen on Android

In this post I want to discuss way of getting the screen content of your Android device to the TV or monitor. If you wonder why one might want to do such a thing – just think about playing some Android games with a bluetooth gamepad or watching a movie where your PC is not available.

Specifically I want to introduce SlimPort. SlimPort is a feature of Nexus devices which is unfortunately not covered much in reviews.
Basically SlimPort is DisplayPort over the Micro-USB connection of your device allowing you to mirror its display.

But the future has arrived: we got Miracast!

One might wonder why one should go through the hassle of using a old-school HDMI cable.
You can get a Chromecast Stick for 35$ and nowadays it also supports Miracast so you can simply stream the images over WiFi.

Well Miracast is all nice if all you need to do is to put up some slides without carrying all possible adapters with you. But as soon as you try to stream a movie or a game you will reach its limitations.

Remember that Miracast works by grabbing the Framebuffer and compressing it with H.264. While encoding happens in hardware it still takes some time and it inevitably introduces compression artifacts. This means:

  • in games you get a noticeable lag – especially in FullHD
  • in movies you get noticeable artifacts – especially in FullHD
  • in both cases your battery will get drained for heavy WiFi and Encoder usage

Going old-school

Going with the old-school cable on the other hand you get HDMI 1.4 transfer rates for up to 1080p at 60Hz while saving the battery.

Configuring the second screen is quite straightforward in android. As Mirroring is your only option, there is actually nothing to configure. Once you connect the adapter android will set up your monitor based on its EDID information and transfer image and audio over HDMI.
In case you only want to have the image over HDMI, simply attach your speakers to the phone and android will re-route the audio.
The days where you had to manually set up everything are over.

Furthermore most adapters have an micro-USB port allowing to still charge your phone while using SlimPort.

Device Support

The downside is that most of the devices do not support SlimPort. The device list more or less boils down to

  • Google Nexus 4/ 5
  • Google Nexus 7 (2013)
  • LG G2/ G3

Samsung devices go with the alternative MHL. Comparing these two SlimPort has the bandwidth advantage of 5Gb/s vs. 3Gb/s of MHL so it does not have to compress that much. However both are clearly better than going wireless.