Setting encoding format [solved]

[wizmer]

Hi everyone,

I'm trying to save in a file my microphone output in a certain format (to be used by the speech recognition library CMU sphinx). The format has to be a single-channel (monaural), little-endian, unheadered 16-bit signed PCM audio file sampled at 16000 Hz.

I'm currently using these parameters:
@ QAudioEncoderSettings settings;
settings.setSampleRate(16000);
settings.setCodec("audio/PCM");
settings.setBitRate(16);
settings.setEncodingMode(QMultimedia::ConstantBitRateEncoding);
audioRecorder->setEncodingSettings(settings,QVideoEncoderSettings());@

The only thing I managed so far is setting it in 16 kHz.
I thought that using settings.setBitRate(16) would produce a 16bit file but audacity tells me that the file is 32bit and stereo.
And about the other parameters, I don't even know how to check them (is it single-channel ? monaural ? PCM ?...)

Can somebody help me to understand these QAudioEncoderSettings methods ?

Thank you !

[SGaist]

Hi and welcome to devnet,

You don't seem to set the channelCount to 1

Hope it helps

[wizmer]

Ah !! Yes indeed, now I get a monaural format. Thank you !

I still have a sample size of 32 bit instead of 16.
By playing with the audiorecorder example I noticed that the codecs
audio/vorbis and audio/FLAC produce 16bit sample sizes while audio/PCM produce 32bit sample sizes.
Is it something fixed for each codec or can it be changed ?

[SGaist]

AFAIK, it should not be fixed, what OS/Qt Version are you on ?

[wizmer]

I am running under Lubuntu 64 bit with Qt 5.1.1
I finally solved the problem by using QAudioInput instead of an QAudioRecorder object. This allowed me to set my settings via QAudioFormat instead of QAudioEncoderSettings. A difference between the two classes is that the latest has a method setSampleSize. I posted a sample code here: http://stackoverflow.com/a/20462224/2533394

[SGaist]

I have overlooked QAudioRecorderSettings, the sample size is indeed not there. I don't know if it's missing on purpose or not. You could ask on the interest mailing list if you would like to know more