Hold Option/Alt while clicking the speaker icon on the menu bar, and it'll give you a list of output devices to choose from

I've had a similar problem where it would sometimes think my lineout speakers also have a microphone. This trick doesn't work because it completely removes the "Internal microphone" option, replacing it with a nonfunctional "External microphone" option.

replied here: https://news.ycombinator.com/item?id=9806321 - switching audio to the hdmi device had no effect

Also buried in System Preferences -> Sound -> Output (or Input), along with some additional controls like balance and a preview of the input level.

/Applications/Utilities/Audio MIDI Setup.app

that's useful.

Unless I'm misunderstanding your audio problem, you can choose the output device by option clicking the volume in the menu bar. You'll get this: http://i.imgur.com/tvkWjqW.png

The same setting is also available through the Sound pane in the System Preferences.

Tried that every time, and it had no effect. Both devices would show up but it'd send audio through the laptop regardless.

I've found a fast way to 'reset' the audio ins/outs is with `sudo pkill coreaudiod`-- stops audio for 1 second but I can always get the right device selected afterwards.

the crappy audio is a yosemite bug

I've experienced similar issues using DisplayPort. I resorted to using Soundflower to properly route the audio - except that the problem persists in such a way that soundflower crashes at least once an hour. People experience zero problems on the same hardware running windows, so it is definitely a software issue.

For those thinking that it is as simple as picking the audio from the output list - that is the desired behavior. When you select your monitor as the output, the selector successfully switches, but your audio output is lost in limbo, or continues to play through the built-in-speakers of your laptop.

Good to know I'm not alone there; sounds like exactly the same issue. For me it would happen with both Mini DisplayPort -> HDMI and HDMI -> HDMI (on the Pro).

On my MBP (original 2012 Retina), when an HDMI display is plugged in, HDMI audio and the internal speakers show up as separate audio devices; I haven't had any problems with this on Mavericks or Yosemite. At the risk of impertinence, are you sure you don't see multiple audio devices? What is the working one named when using HDMI audio vs. the speakers?

They'd both show up, and one (the HDMI option) would not function; it'd always send audio through the laptop. Can't play with it now as it's across the country.

Odd, I ran into a completely different display bug with Yosemite: when I upgraded, my MBP stopped outputting video above 1024x640 to the 27" Dell display I had been previously using at work. I looked around online and found that it was a fairly common (and unresolved) problem, so I ended up switching to two smaller monitors instead.

I recently bought a new MBP which requires a reboot if you wake from sleep with an HDMI monitor attached.

Maybe this is similar to my issue when I connect to my HDMI TV: If I plug in my audio output (1/8" cable) before connecting the HDMI, I'll briefly see a "NO" symbol with the audio (something like this: https://josephhall.org/nqb2/media/blogs/nqb2/stuck-on-mute.j...).

The workaround I've been using is to disconnect the audio cable, wait a second or two, and reconnect the audio cable. After that, I can send audio to my receiver and video to the HDMI.

oh! I see, having this issue, sometimes my skype rings on my external display while using headphones, was quite annoying.

also don't know if my mbp retina hardware or software, but sometimes my display blinks, it also happen with my old mbp (2010) but was not till updated to mountain lion, so maybe is a software issue too? (din't check it, will wait to read some feedback about the update)

I'd be suspicious about the display blinking; I used to get that and it ended up being a faulty power source (no ground, in my case).

Skype issue might just be Skype configuration; they may have their own settings for which device to use, which tends to get out of sync with OS configuration.

oh! will add ground then to my laptop

don't know about the skype, maybe, but this happen sometimes only, seems to be random