[Expired for QEMU because there has been no activity for 60 days.]
** Changed in: qemu
Status: Incomplete => Expired
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https://bugs.launchpad.net/bugs/1861458
Title:
Clock drift issue with -soundhw hda
Status in QEMU:
Expired
Bug description:
Here's the scenario: I'm working on code for loopback audio recording
(i.e. recording what you're hearing) using WASAPI on Windows. As I
usually develop on Linux, I'm using qemu to test this on a Windows 10
VM. The heart of WASAPI audio recording is the
IAudioCaptureClient::GetBuffer function (https://docs.microsoft.com
/en-us/windows/win32/api/audioclient/nf-audioclient-
iaudiocaptureclient-getbuffer). Among other things, this function
produces a timestamp for when the audio buffer it returned is supposed
to be played.
When the audio device in question is the qemu hda device, this
timestamp is wrong.
There is a clock drift error (I measured it to be about 0.1%, i.e. 1ms
drift every second = a full second after 16 minutes) that causes the
audio clock to advance faster than the system clock. Paradoxically,
this does not affect audio playback through qemu at all, no delay
there. Only the timestamps returned to recording applications are
completely bogus.
Unfortunately I'm not intimately familiar with the inner workings of
Intel HD Audio. All I can tell you is that this timestamp is
supposedly obtained directly from the hardware (which would be qemu in
this case), which is also why e.g. chromium implements a workaround
for buggy hardware that returns incorrect timestamps.
Here are the relevant parts of my command line (version 4.2.0):
-enable-kvm -machine pc-q35-3.1,kernel-irqchip=on -cpu
host,kvm=off,hv_time,hv_relaxed,hv_vapic,hv_spinlocks=0x1fff,hv_vendor_id=NvidiaFuckU
-rtc base=localtime -nodefaults -soundhw hda
Just wanted to let you know about this because it took me three days
of utter confusion and frustration to figure this out.
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