can you possibly file a bug report and assign it to me? there are a few
aspects that need to be refined:
* ideally we want to avoid software resampling due to the DSP involved
* iirc coreaudio only resamples on audio output, but not on audio input
* in a perfect world we had an interface to allow customization of the
resampling, but it's not trivial to do this in a cross-platform manner
cheers,
tim
On 4/13/26 20:31, Эдвард Даньковский wrote:
Hello,
I'm working on a messaging application that uses QMediaPlayer to play
audio messages.
These audio messages typically use a 22 kHz sample rate. I've noticed
that playing an
audio message on MacOS causes the output device's sample rate to change.
In some cases,
this significantly degrades the user experience:
1. When using Bose NC700 wireless headphones, the sample rate changes to
16 kHz, which
causes the headphones to disable active noise cancellation.
2. When background music is playing at 48 kHz, its playback quality
significantly
decreases after the sample rate change. Notably, the sample rate
change persists
even after the application exits, leaving the device in an altered
state.
The sample rate change occurs in QCoreAudioSinkStream::open() [1]:
bool QCoreAudioSinkStream::open()
{
// ...
#ifdef Q_OS_MACOS
std::optional<int> bestNominalSamplingRate =
audioObjectFindBestNominalSampleRate(nativeDeviceId,
QAudioDevice::Output, m_format.sampleRate());
if (bestNominalSamplingRate) {
if (!audioObjectSetSamplingRate(nativeDeviceId,
*bestNominalSamplingRate))
return false;
}
// ...
#endif
// ...
}
Here, audioObjectFindBestNominalSampleRate [2] finds the sample rate
closest to
m_format.sampleRate() among the device's supported sample rates, and
audioObjectSetSamplingRate [2] sets the
kAudioDevicePropertyNominalSampleRate
property of the output device. In my case, the output device supports 16
kHz and
44.1 kHz rates, so the 22 kHz audio message is closer to 16 kHz, and Qt
switches
the device to that rate.
As I understand it, this logic serves an optimization purpose — to avoid
resampling
when the output device supports the required sample rate. However, as
described above,
this can lead to unexpected behavior.
On Windows (Shared Mode AudioClient) and with PulseAudio/PipeWire, this
is not a problem
because resampling is handled internally by the audio subsystem. In the
ALSA backend I'm
not sure if it is possible NOT to update the sample rate.
I see two possible solutions:
1. Remove the sample rate change entirely from the MacOS code. This is
the simplest approach.
The documentation does not mention sample rate changes as part of
QAudioSink behavior,
so this shouldn't break documented contracts.
2. Add a new property (e.g., allowHardwareSampleRateChange) to QAudioSink
and QAudioOutput, allowing the sample rate change to be disabled
conditionally
while preserving the current default behavior.
The first option seems cleanest, but it may affect users who rely on the
current
behavior for low-latency playback without resampling.
The second option preserves backward compatibility but introduces
complexity:
- With ALSA, I'm not sure if it's possible to avoid setting the sample rate
for a hardware device.
- With PipeWire, it may be impossible to guarantee the sample rate won't
change,
since PipeWire can update it when only one stream is active.
- Every media player backend would need updates to support this property.
My questions:
1. Is this considered a bug that needs fixing?
2. If so, can we simply remove the sample rate change from
QCoreAudioSinkStream::open?
3. If removal is not acceptable, what are your thoughts on adding an
allowHardwareSampleRateChange property?
[1] qtmultimedia/src/multimedia/darwin/qdarwinaudiosink.mm <https://
eur01.safelinks.protection.outlook.com/?
url=http%3A%2F%2Fqdarwinaudiosink.mm%2F&data=05%7C02%7C%7Ccc107b41a43e48fad19408de9959210f%7C20d0b167794d448a9d01aaeccc1124ac%7C0%7C0%7C639116805446889327%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C80000%7C%7C%7C&sdata=cQTbKLNDL6m6WPQQ1nYEZN%2FOhtG2COFqoSiuS1RrB0g%3D&reserved=0>
[2] qtmultimedia/src/multimedia/darwin/qcoreaudioutils.cpp
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