This is an old question, so maybe you have already solved your problem. But in case you have not or in case others are running into this issue and not finding solutions which work for them (as was the case with me recently), here is another thing one can try.
This is mostly taken from the suggestion here, but slightly expanded/modified. It seems PulseAudio has a bug which can cause it to fail to automatically detect hdmi audio outputs ("sinks" in its language), so you can fix things by manually telling it about your hdmi device.
Step 1: Make sure PulseAudio hasn't detected your hdmi sink
You can list all sinks loaded into PulseAudio with pactl list short sinks. This should produce a list of things of the form
0 alsa_output.pci-0000_06_00.6.HiFi__hw_Generic__sink module-alsa-card.c s16le 2ch 48000HzIDLE
If your hdmi audio does not show up in your list, then we may have found the problem, so keep reading. If you are not sure if it does or not, you can also run pactl list sinks | grep description for more human-readable descriptions of the devices detected. I think hdmi sinks will have a description of the form "blah High Definition Audio Controller" while non-hdmi sinks might have a description like "blah blah blah Speaker + Headphone".
Step 2: Make sure your computer can output audio to hdmi
Run aplay -l to get a list of hardware playback devices. For me, the output looks like
**** List of PLAYBACK Hardware Devices ****
card 0: NVidia [HDA NVidia], device 3: HDMI 0 [HDMI 0]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 7: HDMI 1 [HDMI 1]
Subdevices: 0/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 8: HDMI 2 [HDMI 2]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 9: HDMI 3 [HDMI 3]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 10: HDMI 4 [HDMI 4]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 0: NVidia [HDA NVidia], device 11: HDMI 5 [HDMI 5]
Subdevices: 1/1
Subdevice #0: subdevice #0
card 1: Generic [HD-Audio Generic], device 0: ALC245 Analog [ALC245 Analog]
Subdevices: 0/1
Subdevice #0: subdevice #0
In particular, there are many sorts of hdmi devices available. We want to find the one that actually corresponds to the hdmi port you have a cable plugged in to.
The first thing to do is to run alsamixer to make sure your hdmi device isn't muted. You should see a screen like the one below.
Use F6 to select the correct sound card. If you see MM in any of the slots, that means it's muted. Select it and press M to unmute. Hit Esc when you're done.
Really, you probably should only need to unmute one of these slots (the one actually associated with your hdmi port which is probably the first one), but it doesn't hurt to unmute them all.
With that taken care of, we can now test your audio. Run
speaker-test --channels 2 --test wav --device hw:[card],[device]
where [card],[device] refers to the numbers from the output of aplay -l, e.g. I'd first use hw:0,3. You'll do this for every hdmi hardware device listed previously until one of them actually produces an audible sound.
Step 3: Add HDMI sink to PulseAudio and make sure it works (can skip if you want)
Now that you have identified and card and device number associated to your hdmi port, simply run
pactl load-module module-alsa-sink device=hw:[card],[device]
You should now be able to go to your sound settings and see a new selectable output device (Mine's called TU116 High Definition Audio Controller). Select it and see if your hdmi audio works now. If not, I can't help you. But if it does, congrats.
Step 4: Make this change (almost) permanent
At the moment, if you restart your computer, you'd have to rerun this load_module command in order for hdmi to work again. To make things a little better, edit `/etc/pulse/default.pa' (as root), and near the end of the file, add the line
load-module module-alsa-sink device=hw:[card],[device]
After this (especially if you skipped step 3), you might want to run
rm -r ~/.config/pulse
killall pulseaudio
pulseaudio --start
to restart PulseAudio.
Lastly, a few hiccups/remarks
- For me, even after doing this, I still need to run
killall pulseaudio; pulseaudio --start after rebooting my computer in order for PulseAudio to load in the hdmi sink. I don't know how to fix this.
- For me, the hdmi device is still listed as an option in Ubuntu's sound settings even when my cable isn't plugged in. I don't know how to fix this.
- The link from the beginning of this answer mentions a script for automatically switching to hdmi audio when a cable is plugged in. I don't know enough about linux to follow what's going on in that script, so I haven't tried this myself.
