Strange sound in the first seconds of streaming audio

[renebarto]

I have an issue similar to #11724 on Windows.
I'm placing two sine waves of different frequencies on each channel of a stereo pair.
When I create the stream (16 bit setero) I get callbacks for 1920 bytes per call, and fill up the buffer then add 480 sample frames of 4 bytes each with sine wave (using a continuing phase to make sure the audio is smooth).
In the first seconds I hear a strange deformation on both channels, which disappears after a few seconds, first on the left, and a few seconds later on the right channel. After that the sounds is what I'd expect.
I tried clearing the buffer first, but that does not help.
I have the feeling either SDL_PutAudioStreamData writes more or less data to the buffer than specified, or that later on something else messes up the audio.

To be clear, I do not open a device first, I just create as stream:

SDL_AudioSpec spec { SDL_AUDIO_S16LE, 2, 48000 };
m_stream = SDL_OpenAudioDeviceStream(id, &spec, callback, nullptr);

Callback:
static uint8_t audioBuffer[65536];
float phaseL = 0.0F;
float phaseR = 0.0F;
float sampleFreq = 48000.0F;
float freqL = 1000.0F;
float freqR = 2000.0F;
float twoPI = 2 * SDL_PI_D;
float stepL = freqL / sampleFreq * twoPI;
float stepR = freqR / sampleFreq * twoPI;

void audio_callback(void */userdata/, SDL_AudioStream *stream, int additional_amount, int total_amount)
{
size_t offset{};
int sampleFrames = additional_amount / 4;
for (int i = 0; i < sampleFrames; ++i)
{
int16_t sampleL = static_cast<int16_t>(32768.0F * sin(phaseL) + 0.5F);
int16_t sampleR = static_cast<int16_t>(32768.0F * sin(phaseR) + 0.5F);
memcpy(audioBuffer + offset, &sampleL, 2);
offset += 2;
memcpy(audioBuffer + offset, &sampleR, 2);
offset += 2;
phaseL += stepL;
phaseR += stepR;
if (phaseL > twoPI)
phaseL -= twoPI;
if (phaseR > twoPI)
phaseR -= twoPI;
}
// Put the audio data into the stream
//std::cout << "Get audio, size " << additional_amount << "\r\n";
SDL_PutAudioStreamData(stream, audioBuffer, sampleFrames * 4);
}

I play sound for about 10 secs, then pause and destroy the stream.

After about 2 seconds the left channel sounds normal, after about 4 seconds the right is also normal.

[renebarto]

Sorry, forgot to mention I'm on SDL3.1.9

[renebarto]

For additional information, I just checked out the 3.2.0 commit and rebuilt. Same issue.

[milq]

@renebarto, same for me using Debian GNU/Linux.