I'm looking at a new camera that has a mic in and audio control, but no headphones out. Is there a way to get live audio out of a camera using the HDMI port and plugging into headphones? I want to be portable, so plugging into a monitor and then from the monitor to the headphones is not practical.
What you want is generally called an "HDMI audio extractor". There are several hardware products on the market that will extract the audio in the HDMI stream to an audio out connection and pass-through the video part.
A search on ebay gives you several results: http://www.ebay.com/sch/i.html?_nkw=HDMI+audio+extractor
Though if you need very high quality audio you probably need a more professional product with a good built-in DAC (digital to analog converter). HDMI audio is digital so it needs to be converted to an analog signal and the hardware used in these products isn't meant for high fidelity audio production. Or buy a cheap one with an digital output and use an external DAC.
What you can always do is intercept the signal before it goes into the camera. Buy a small mixer, plug the mic into it and use the headphone out of the mixer to monitor the mic. Then take the master stereo out of the mixer and run it into your camera. You should get on the camera what you hear on the phones. You may want one of the HDMI audio extractors to confirm it but once its been confirmed you can use the mixer as you wish.