This bug report was migrated from our old Bugzilla tracker.

These attachments are available in the static archive:

• Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl. (sdl-hwfreq.diff, text/plain, 2020-04-08 14:19:52 +0000, 1952 bytes)
• [v2] Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl. (sdl-hwfreq.diff, text/plain, 2020-04-08 14:30:46 +0000, 1952 bytes)
• [v3] Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl (sdl-getformat.patch, text/plain, 2021-01-08 12:46:29 +0000, 2165 bytes)

Reported in version: HG 2.0
Reported for operating system, platform: NetBSD, x86

Comments on the original bug report:

On 2020-04-08 14:19:52 +0000, Nia Alarie wrote:

Created attachment 4298
Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl.

The NetBSD kernel's audio resampling code is much simpler and lower quality than libsamplerate.

Presumably, if SDL always performs I/O on the audio device in its native frequency, we can avoid resampling audio in the kernel and let SDL do it with libsamplerate instead.

On 2020-04-08 14:30:46 +0000, Nia Alarie wrote:

Created attachment 4299
[v2] Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl.

Actually, we shouldn't set the device "blocksize" at all (the kernel will ignore it and calculate its own), but especially don't set it to the value of spec->size before spec->size is calculated.

On 2020-12-27 09:24:22 +0000, Nia Alarie wrote:

The last version of this patch I uploaded doesn't work with older NetBSD releases so shouldn't be applied.

On 2020-12-27 21:11:58 +0000, Sam Lantinga wrote:

These changes sound useful. Is there a way to make this work with both old and new versions of NetBSD?

On 2020-12-27 21:12:25 +0000, Sam Lantinga wrote:

Waiting for confirmation before resolving this bug.

On 2021-01-06 13:46:09 +0000, Nia Alarie wrote:

Yes, we can easily make this work on older versions of NetBSD by #ifdefing around the AUDIO_GETFORMAT ioctl usage.

I wonder if this is actually how SDL is supposed to work, though. I just assumed that SDL now does the conversions automatically, so to revisit this patch I'd need reassurance about the internal behaviour.

On 2021-01-06 17:29:29 +0000, Sam Lantinga wrote:

SDL will automatically convert sample rate if the application requests it, so returning the native sample rate is completely reasonable here.

On 2021-01-06 17:30:33 +0000, Sam Lantinga wrote:

Basically the audio driver should change to the requested frequency if the audio hardware can run at that frequency, and return the actual frequency if not.

On 2021-01-08 12:46:29 +0000, Nia Alarie wrote:

Created attachment 4643
[v3] Patch to get and use the current hardware frequency with the AUDIO_GETFORMAT ioctl

Attempt to work with older NetBSD releases.

On 2021-01-08 12:50:42 +0000, Nia Alarie wrote:

OK, new patch uploaded.

Background: The audio device supports any arbitrary sample rate from 1-192kHz. The user can configure a native frequency for the device, which is nearly always 48kHz by default. Audio at a different frequency will play without issue, but will be resampled in the kernel, and we definitely want libsamplerate to be used instead.

v3 of the patch should always set this->spec.freq to the native rate (usually 48kHz) on NetBSD 9.x and newer, but will leave it unchanged on older releases and rely on the in-kernel resampler. Does that sound right?

On 2021-01-08 18:10:30 +0000, Sam Lantinga wrote:

Yup, looks good, thanks!
https://hg.libsdl.org/SDL/rev/eec6a0d937e2