Audio conversion issues?

[bonezone2001]

I am completely new to audio processing and I'm trying to get the loopback recording as signed int16 PCM
I have searched around the documentation and issues section to maybe find out how to properly do this but even when the logic seems sound I get corrupted output. Maybe it's an output size issue? I'm a little confused as to what I'm doing wrong? I'm probably being a complete idiot. For further context, each PCM frame will eventually be encoded with opus and sent over the network.

#include <iostream>
#include "opus_codec.h"

#define MA_NO_GENERATION
#define MINIAUDIO_IMPLEMENTATION
#include "miniaudio.h"

#include <cstdlib>
#include <cstdio>

void data_callback(ma_device* pDevice, void* pOutput, const void* pInput, ma_uint32 frameCount)
{
	// Setup
	auto* pFile = (FILE*)pDevice->pUserData;
	MA_ASSERT(pFile != nullptr);
	std::cout << "Captured frame of size " << frameCount << " - " << (frameCount * 2 * sizeof(short)) << "\n";

	// TEMPORARY TEST: Covert and write pcm data
	static auto* buf = calloc(1, frameCount * 2 * sizeof(short));
	ma_convert_pcm_frames_format(buf, ma_format_s16, pInput, pDevice->capture.format, frameCount, 2, ma_dither_mode_triangle);
	fwrite(buf, frameCount * 2 * sizeof(short), 1, pFile);
}

int main()
{
	ma_result result;

	ma_encoder_config encoderConfig;
	ma_device_config deviceConfig;
	ma_device device;
	FILE* pcmFile = fopen("test.pcm", "w");

	// Select wasapi as the backend (since it supports loopback)
	ma_backend backends[] = {
		ma_backend_wasapi
	};

	// Setup device capture config
	deviceConfig = ma_device_config_init(ma_device_type_loopback);
	deviceConfig.capture.pDeviceID = NULL;
	deviceConfig.capture.channels = 0;
	deviceConfig.sampleRate = 0;
	deviceConfig.dataCallback = data_callback;
	deviceConfig.pUserData = pcmFile;

	// Initialize device
	result = ma_device_init_ex(backends, sizeof(backends) / sizeof(backends[0]), NULL, &deviceConfig, &device);
	if (result != MA_SUCCESS)
	{
		printf("Failed to initialize loopback device.\n");
		fclose(pcmFile);
		return -2;
	}

	// TEST: Output information about the selected device
	printf("%u %u %u\n", device.capture.format, device.capture.channels, device.sampleRate);

	// Start capturing
	result = ma_device_start(&device);
	if (result != MA_SUCCESS)
	{
		ma_device_uninit(&device);
		fclose(pcmFile);
		printf("Failed to start device.\n");
		return -3;
	}

	// Wait until we exit
	printf("Press Enter to stop recording...\n");
	getchar();

	// Cleanup
	ma_device_uninit(&device);
	fclose(pcmFile);

	return 0;
}

Here is the output, I suspect maybe I'm writing more data than available? but then again I'm using calloc so it would just be 0s?

[mackron]

Can you post the output with #define MA_DEBUG_OUTPUT? One bug you certainly have is that you've specified a channel count of 0 in the device config which tells miniaudio to use the device's native channel count which could be anything, but in the data callback you've hard coded it to 2. Try changing the channel count in the device config to 2.

A second bug is that you're opening the file in text mode and not byte mode. Open the file with "wb" instead of "w".

A piece of general advice - get miniaudio to do the data conversion for you internally. If you always want to use ma_format_s16 for your final output, just set the format in the device config: deviceConfig.capture.format = ma_format_s16 and be done with it. Same with the channel count.

[bonezone2001]

Thank you for your timely answer,
I knew I was just being a complete idiot. It was just because of the text mode being supplied. The other 2 things you mentioned were artifacts of getting the thing to work :P I presumed it would do the conversion for me but when things weren't working, I was wondering if the conversion was wrong, Thank you so much