Similar to the Roku app, this new Android TV app lets you watch live TV on your SHIELD via the Channels DVR backend (running either on the SHIELD itself, or any other computer/NAS in your home). Install it via https://play.google.com/apps/testing/com.getchannels.android
Since the SHIELD can decode both mpeg2 and h264 natively, the DVR server does not need to do any transcoding. It simply finds an available tuner (sharing when possible) and forwards the video to the SHIELD for viewing.
The app also uses up to 2GB of local storage on the SHIELD for buffering, allowing you to pause/resume and skip -10/+30s during playback.
NOTE: This app is still very experimental, as I'm still trying to learn how Android apps work and there's a lot involved. The app only works if you have Channels DVR running on your network (it cannot talk to HDHRs directly). Playback has only been tested on the SHIELD, but it may work on other Android TV boxes.