I have to keep note of this, since it’s quite a voodoo bug in Android studio emulator:

If you specify a http proxy in the emulator command line options, the emulator won’t work.

Weirdly enought, the only way to make it work is to specify the -no-audio option:

C:\Users\<your user folder>\AppData\Local\Android\sdk\tools>emulator -avd  <avd-name>-http-proxy 192.168.1.78:8888 -no-audio

The <avd name> is the filename of one of the ini files in C:\Users\<your user folder>\.android\avd, and of course you need to subsitute the address of your proxy server!