SDL simple record and playback

SDL Audio.cpp

#include <SDL.h>
#include <cstdio>
#include <iostream>
#include <string>
#include <cstring>
#include <sstream>
#include <ctime>

const int MAX_RECORDING_DEVICES = 10;

//Maximum recording time
const int MAX_RECORDING_SECONDS = 60;

//Maximum recording time plus padding
const int RECORDING_BUFFER_SECONDS = MAX_RECORDING_SECONDS + 1;

//Recieved audio spec
SDL_AudioSpec gReceivedRecordingSpec;
SDL_AudioSpec gReceivedPlaybackSpec;

//Recording data buffer
Uint8* gRecordingBuffer = NULL;

//Size of data buffer
Uint32 gBufferByteSize = 0;

//Position in data buffer
Uint32 gBufferBytePosition = 0;

//Maximum position in data buffer for recording
Uint32 gBufferByteMaxPosition = 0;

int gRecordingDeviceCount = 0;

char y;

void audioRecordingCallback(void* userdata, Uint8* stream, int len )
{
	//Copy audio from stream
	std::memcpy(&gRecordingBuffer[ gBufferBytePosition ], stream, len);

	//Move along buffer
	gBufferBytePosition += len;
}

void audioPlaybackCallback(void* userdata, Uint8* stream, int len )
{
	//Copy audio to stream
	std::memcpy(stream, &gRecordingBuffer[ gBufferBytePosition ], len);

	//Move along buffer
	gBufferBytePosition += len;
}

int main()
{
	if(SDL_Init(SDL_INIT_AUDIO) < 0)
	{
		printf("SDL could not initialize! SDL Error: %s\n", SDL_GetError());
		return 1;
	}

	SDL_AudioDeviceID recordingDeviceId = 0;
	SDL_AudioDeviceID playbackDeviceId = 0;

	SDL_AudioSpec desiredRecordingSpec;

	SDL_zero(desiredRecordingSpec);
	desiredRecordingSpec.freq = 44100;
	desiredRecordingSpec.format = AUDIO_S16;
	desiredRecordingSpec.channels = 2;
	desiredRecordingSpec.samples = 4096;
	desiredRecordingSpec.callback = audioRecordingCallback;

	gRecordingDeviceCount = SDL_GetNumAudioDevices(SDL_TRUE);

	if(gRecordingDeviceCount < 1)
	{
		printf( "Unable to get audio capture device! SDL Error: %s\n", SDL_GetError() );
		return 0;
	}

	int index;

	for(int i = 0; i < gRecordingDeviceCount; ++i)
	{
		//Get capture device name
		const char* deviceName = SDL_GetAudioDeviceName(i, SDL_TRUE);

		printf("%d - %s\n", i, deviceName);
	}

	printf("Choose audio\n");
	scanf("%d", &index);

	//Open recording device
	recordingDeviceId = SDL_OpenAudioDevice(SDL_GetAudioDeviceName(index, SDL_TRUE), SDL_TRUE, &desiredRecordingSpec, &gReceivedRecordingSpec, SDL_AUDIO_ALLOW_FORMAT_CHANGE);
	
	// Device failed to open
	if(recordingDeviceId == 0)
	{
		//Report error
		printf("Failed to open recording device! SDL Error: %s", SDL_GetError() );
		return 1;
	}

	//Default audio spec
	SDL_AudioSpec desiredPlaybackSpec;
	SDL_zero(desiredPlaybackSpec);
	desiredPlaybackSpec.freq = 44100;
	desiredPlaybackSpec.format = AUDIO_S16; // AUDIO_F32;
	desiredPlaybackSpec.channels = 2;
	desiredPlaybackSpec.samples = 4096;
	desiredPlaybackSpec.callback = audioPlaybackCallback;

	//Open playback device
	playbackDeviceId = SDL_OpenAudioDevice( NULL, SDL_FALSE, &desiredPlaybackSpec, &gReceivedPlaybackSpec, SDL_AUDIO_ALLOW_FORMAT_CHANGE );

	//Device failed to open
	if(playbackDeviceId == 0)
	{
		//Report error
		printf("Failed to open playback device! SDL Error: %s", SDL_GetError());
		return 1;
	}

	//Calculate per sample bytes
	int bytesPerSample = gReceivedRecordingSpec.channels * (SDL_AUDIO_BITSIZE(gReceivedRecordingSpec.format) / 8);

	//Calculate bytes per second
	int bytesPerSecond = gReceivedRecordingSpec.freq * bytesPerSample;

	//Calculate buffer size
	gBufferByteSize = RECORDING_BUFFER_SECONDS * bytesPerSecond;

	//Calculate max buffer use
	gBufferByteMaxPosition = MAX_RECORDING_SECONDS * bytesPerSecond;

	//Allocate and initialize byte buffer
	gRecordingBuffer = new Uint8[gBufferByteSize];
	std::memset(gRecordingBuffer, 0, gBufferByteSize);

	// FILE* f = fopen("output.txt", "rb");
	// size_t result = fread(gRecordingBuffer, sizeof(Uint8), gBufferByteSize, f);
	// if (result != gBufferByteSize)
	// {
	// 	printf("Something wrong? Res: %lu & gBufferByteSize %u\n", result, gBufferByteSize);
	// }

	std::printf("Recoding\n");
	std::cin >> y;

	// begin recording

	//Go back to beginning of buffer
	gBufferBytePosition = 0;

	SDL_PauseAudioDevice( recordingDeviceId, SDL_FALSE );

	while(true)
	{
		//Lock callback
		SDL_LockAudioDevice( recordingDeviceId );

		//Finished recording
		if(gBufferBytePosition > gBufferByteMaxPosition)
		{
			//Stop recording audio
			SDL_PauseAudioDevice( recordingDeviceId, SDL_TRUE );
			break;
		}

		//Unlock callback
		SDL_UnlockAudioDevice( recordingDeviceId );
	}

	std::printf("Playback\n");
	std::cin >> y;

	gBufferBytePosition = 0;
	SDL_PauseAudioDevice(playbackDeviceId, SDL_FALSE);

	const clock_t begin_time = clock();
	while(true)
	{
		//Lock callback
		SDL_LockAudioDevice(playbackDeviceId);

		//Finished playback
		if(gBufferBytePosition > gBufferByteMaxPosition)
		{
			//Stop playing audio
			SDL_PauseAudioDevice(playbackDeviceId, SDL_TRUE);
			std::cout << "Time elapsed: " << float(clock() - begin_time) / CLOCKS_PER_SEC << '\n';
			break;
		}

		//Unlock callback
		SDL_UnlockAudioDevice(playbackDeviceId);
	}

	if( gRecordingBuffer != NULL )
	{
		delete[] gRecordingBuffer;
		gRecordingBuffer = NULL;
	}

	SDL_Quit();
	return 0;
}

There are missing SDL_UnlockAudioDevice(playbackDeviceId); and SDL_UnlockAudioDevice( recordingDeviceId ); inside the loops. I made a fork with that fixes it.