[Qemu-devel] What is the status of the QEMU sound rework?

[Zir Blazer]

I'm a VGA Passthrough user that uses a QEMU VM to fully replace a Windows 
native install as the main OS.


Currently, one of the biggest hazzles for many users is that sound is hard to 
get working properly with the emulated AC'97 and Intel HDA Sound Cards due to 
crackle or latency issues (Latency issues heavily affects recording scenarios, 
like voice chat applications in a VM). An example here, through there are far 
more: 
https://www.reddit.com/r/VFIO/comments/746t4h/getting_rid_of_audio_crackling_once_and_for_all/


Some people managed to get sound working at acceptable levels by meddling with 
the environmental variables, but most of the solutions come from a 
trial-and-error esoteric procedure instead of structured troubleshooting, as 
each user has to figure out which settings makes the emulated Sound Cards work 
decently in his system. For those that failed getting the desired results with 
emulation, they have to throw Hardware at the issue by using PCI Passthrough of 
a Sound Card, or an USB Sound Card via USB Passthrough (Or even have it plugged 
to an USB Controller passed to the VM via PCI Passthrough), or using the 
passthroughed Video Card HDMI with a Monitor with speakers, just to solve the 
sound issues. The problem is that this complicates this type of setups a lot, 
and it makes impossible a typical use case that would be that all the VMs 
output the sound to the host, which has control of the Motherboard integrated 
Sound Card, and it mixes it to use a single set of speakers for the entire 
system.



I have been googling around and found that at several times, there were ideas 
and proposal, and even some code, that were intended to overhaul QEMU sound 
system. Examples includes:

GSoC 2011 Xen PV Audio, a paravirtualized Sound Card 
https://wiki.xenproject.org/wiki/Archived/GSoc_2011_Ideas
GSoC 2015 QEMU rework of the sound environmental variables 
https://wiki.qemu.org/Google_Summer_of_Code_2015#QEMU_audio_backend
GSoC 2017 QEMU rework a patch series that did precisely that 
https://wiki.qemu.org/Google_Summer_of_Code_2017#QEMU_audio_backend
https://lists.nongnu.org/archive/html/qemu-devel/2016-01/msg02451.html



Basically, what happened with all the previous ideas and proposals? Did any of 
that work ever get into upstream QEMU?
Is anyone tinkering with the idea of making a paravirtualized Sound Card and 
its associated Drivers for the mainstream OSes to try to fix once and for all 
the sound issues?