The AllCast for FireTV receiver app will soon let you use your headphones as a wireless headset with your Amazon Fire TV. Using the app, you will be able to stream audio from the Fire TV to your phone without streaming the video, letting you watch a movie or TV episode without the sound disturbing others.
Developer Koushik Dutta demonstrates the upcoming feature in the video above. He also notes that replicating this same feature with Chromecast is more difficult because advanced audio/video parsing is not possible on the device. But with Fire TV
You can download AllCast for FireTV for free from the Amazon Appstore now.
Source: Koushik Dutta