QAudioOutput underrun issue on Realtime Play from Microphone with QAudioInput

michaelL

Hi,

sometimes i am getting "underrun occured" from ALSA lib and that means the audioouput is not getting the values on time to play. Alsa then repeats the old buffer values on the speaker.

How can i avoid underruns on QAudioOuput?

I tryied to change the buffersize:

audioOutput->setBufferSize(144000);
qDebug()<<"buffersize "<<audioOutput->bufferSize()<<" period size"<<audioOutput->periodSize();

I get:
buffersize 144000 period size 0

and after audiOutput->start() i get:
buffersize 19200 period size 3840

Here is what i am doing:

audioOutput->setBufferSize(144000);
qDebug()<<"buffersize "<<audioOutput->bufferSize()<<" period size"<<audioOutput->periodSize();
m_audioInput = audioInput->start();
 m_audioOutput = audioOutput->start();
 qDebug()<<"buffersize "<<audioOutput->bufferSize()<<" period size"<<audioOutput->periodSize();
 connect(m_audioInput, SIGNAL(readyRead()), SLOT(readBufferSlot()));

Once audio data gets recorded i write to the QIODevice m_audioOutput the values from QIODevice m_audioInput .
So i think i have a timing issue simetimes and the audio interval for both is 1000ms before and after start(). Why cant i increase the buffer size? And how can i avoid underrun?

SGaist

Hi,

What version of Qt are you using ?
On what Linux distribution ?
On what type of machine ?
What audio hardware are you using ?

michaelL

@SGaist said in QAudioOutput underrung issue on Realtime Play from Microfone with QAudioInput:

dio hardware are you using ?

@SGaist i am using:
QT Version 5.9.1
Linux Distribuition: Debian Jessie 8
Machine: ARM iMx6Q
Audio: Two Soundcards, one USB and one connected to ARM via I2S and I2C(NXP iMx6 Eval).

The USB Audio Soundcard, "Microfone" works fine also with other computers. The second one, for speakers, also works fine.

So i found this on QAudioOutput class:

int QAudioOutput::periodSize() const

Returns the period size in bytes. This is the amount of data required each period to prevent buffer underrun, and to ensure uninterrupted playback.
Note: It is recommended to provide at least enough data for a full period with each write operation.

I cannot set peridoSize but i can only read. QaudioInput must be synchronize with QAudioOutput so that QAudioOutput doesnt get underrun. As far as i know, underruns means that for example QAudioOutput doenst get engought data at a certain time to play and it will throw a message and repeat the last buffer of data to the speakers.

Any idea?

SGaist

Is it the Qt version provided with your distribution ?

michaelL

@SGaist said in QAudioOutput underrun issue on Realtime Play from Microphone with QAudioInput:

the Qt version provided with your distribution ?
@SGaist Yes this QT version is provided. How do i increase the buffer in QAudioOutput and the periodSize()?

SGaist

Did you check which backend you are using ?

In case it's ALSA, you have to ensure that QAudioOutput is in stopped state before calling setBufferSize.

michaelL

@SGaist said in QAudioOutput underrun issue on Realtime Play from Microphone with QAudioInput:

setBufferSize

@SGaist Yes it is ALSA and it is in idle/stop state.
So do you mean that the solution would be changing the Buffersize right?

SherifOmran

how did you solve the underrun issue, i have it also in embedded and not on PC ? i have the same issue and when i increase the buffer size, it does not help on embedded.