Set up a QBuffer as a FIFO with a restricted size ? QT - c++

Question

I have a continuous audio stream flow from which I'd like to keep only the last 50 seconds.
I do it like so for now but I have issues:
The buffer grows beyond 50 seconds. I tried to use resize on a QByteArray to get closer from a FIFO , but it doesn't seem to care much about it and continue to grow so I guess I misunderstood the doc.
The sound get suddenly ugly when we pass the 15 sec -> I have no clue why the sound suddenly rips (if I load a 5min local sound in the same buffer, everything works great).
Last, but not least of course, the buffer doesn't behave like a FIFO and this is what I'm looking for to keep only the last 50sec
Here is my code: (Windows10 - Qt5)
buffer = new QBuffer;
arr = new QByteArray;
arr->resize(200000);
buffer->setData(*arr); // buffer->setBuffer(*arr);
buffer->open(QIODevice::ReadWrite);
dataStream.setDevice(buffer); `
m_player = new QMediaPlayer(this);
m_player->setMedia(QMediaContent(), buffer);
[...]
connect(m_player, &QMediaPlayer::durationChanged, this, &MainWindow::durationChanged);
connect(m_player, &QMediaPlayer::positionChanged, this, &MainWindow::positionChanged);
I refresh the buffer duration in the latest slot.
So the buffer gets bigger than 50sec of course and the sound get chopped after 15 sec.
Does anyone know how to set up a FIFO buffer with a restricted size with Qt?
---------------------------------------------------------- EDIT ------------------------------------------------------------------
I found this to get closer but I miss something in it :
//.cpp :
#define SAMPLE_RATE 22050
#define CHANNELS 1
#define SAMPLE_SIZE 16
#define SAMPLE_TYPE SignedInt
myAudio::myAudio()
{
formatIn.setSampleRate(SAMPLE_RATE);
formatIn.setChannelCount(CHANNELS);
formatIn.setSampleSize(SAMPLE_SIZE);
[...]
formatIn.setByteOrder(QAudioFormat::LittleEndian);
formatIn.setSampleType(QAudioFormat::SAMPLE_TYPE);
formatOut. //same than formatIn
[...]
//configure device
audioOut = new QAudioOutput(deviceOut,formatOut,0);
audioIn = new QAudioInput (deviceIn, formatIn,0);
buff.resize(0x10000); //create a rx buffer
pbuff=buff.data(); //get the buff address;
RXbuff=0; //set RX buffer pointer
qDebug()<<"File open"<<open(QIODevice::ReadWrite);
qDebug()<<"is device Sequential="<<isSequential();
audioIn->start(this); //start reading device
audioOut->setVolume(0.5); //volume 0 to 1.0
audioOut->start(this); //start writing to device
}
//QIODevice Class (Protected Functions)This function is called by QIODevice.
//send to output(Speaker)
qint64 myAudio::readData(char *data, qint64 len)
{
static quint64 TXbuff=0;
qint64 total = 0;
while (len > total && RXbuff>TXbuff)//write and synchonise buffers
{
//write data to speaker
memcpy(&data[total],&pbuff[TXbuff%0x10000], 2); //copy 2 Bytes
TXbuff+=2; //point to next buffer 16 bit location
total+=2;
}
return total; //the reset interval
}
//audio input (from Microphone)
qint64 myAudio::writeData(const char *data, qint64 len)
{
int total=0;
while (len > total)
{
memcpy(&pbuff[RXbuff%0x10000],&data[total], 2); //write 2Bytes into
circular buffer(64K)
RXbuff+=2; //next 16bit buffer location
total+=2; //next data location
}
return (total); //return total number of bytes received
}
qint64 myAudio::bytesAvailable() const{return 0;}
What I miss is pretty basic... does anyone know When/How are the methods called ?!