sdl2 audio infrastructure quesiton for usb audio devices

SDL Development
1

Folks:

I am on ubuntu linux (22.04). I have a usb camera with a built in microphone.

I want to use the sdl queue ( non callback). I am attempting to use the sdl_dequeue tor retrieve sound for my own buffer.

The purpose of this is for an oscilloscope.

I can open the device okay (no error) for capture.

However my calls to sdl_dequeu constantly return 0.

What I wonder is the sdl2 audio infrastructure okay with usb cameras’ audio device?

Or would I be better off not bothering with the sdl audio infrastructure and go ahead and use the linux also infrastructure?

Thank you
Mark Allyn

2

Make sure you’ve opened the audio device for recording instead of playback. When calling SDL_OpenAudioDevice() pass a non-zero value for the iscapture parameter.

3

I did check that. Still nothing was read.

4

Would you mind to add, just after

SDL_Init(SDL_INIT_AUDIO);

The following line :

SDL_Log("Using audio driver: %s\n", SDL_GetCurrentAudioDriver());

And tell us what happens ?

If not successfull, I’d suggest to add :

// alsa, or pulse, or whatever audio driver SDL compatible you'd like to use
putenv((char *)"SDL_AUDIODRIVER=alsa");

before SDL_Init().

HTH

5

Did you unpause the audio device with SDL_PauseAudioDevice() after opening?

6

Yes, I did unpause the device.

Mark

7

Maybe it’s a muted device?
System settings->Sound->Input
Select the USB monitor device.
Make sure the slider is not pulled all the way left.

Double check that it’s drivers are set up properly and working by recording a sample using audacity?

Have you tried unplugging it and plugging it back in?

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