December 19, 2011

Anticross Anticross
Hobby Entomologist
250 posts
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send raw data to QAudioOutput.

 

I’ve got QAudioOutput which initialized by next format:

  1. QAudioFormat format;
  2.                        // Set up the format, eg.
  3.                        format.setFrequency(44100);
  4.                        format.setChannels(2);
  5.                        format.setSampleSize(16);
  6.                        format.setCodec("audio/pcm");
  7.                        format.setByteOrder(QAudioFormat::LittleEndian);
  8.                        format.setSampleType(QAudioFormat::UnSignedInt);
  9.  
  10.                        QAudioDeviceInfo info(QAudioDeviceInfo::defaultOutputDevice());
  11.                        if (!info.isFormatSupported(format)) {
  12.                            qWarning()<<"raw audio format not supported by backend, cannot play audio.";
  13.                            return;
  14.                        }

I’ve got a class subclassed from QIODevice to store incoming data which uses like a buffer:
  1. #ifndef AUDIOBUFFER_H
  2. #define AUDIOBUFFER_H
  3.  
  4. #include <QAudioFormat>
  5. #include <QIODevice>
  6. #include <QMutex>
  7.  
  8. class AudioBuffer : public QIODevice
  9. {
  10.     Q_OBJECT
  11. public:
  12.     struct block
  13.     {
  14.         char * ptr;
  15.         qint64 len;
  16.         int    index;
  17.     };
  18. //----------------------------------------------------------------------------------------------------------------------------------
  19.     AudioBuffer(/*const QAudioFormat &format,*/ QObject *parent = NULL) :   QIODevice(parent)
  20.     {
  21. //         const char * someData = "12MMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMMWQuhaSSSSSSSSSSSSSSSSSSSSSSSSSSss";
  22. //         writeData(someData,sizeof(someData));
  23.     }
  24. //----------------------------------------------------------------------------------------------------------------------------------
  25.     ~AudioBuffer()
  26.     {
  27.         clear();
  28.     }
  29. //----------------------------------------------------------------------------------------------------------------------------------
  30.     void start()
  31.     {
  32.         if(!isOpen())
  33.             open(QIODevice::ReadWrite);
  34.     }
  35. //----------------------------------------------------------------------------------------------------------------------------------
  36.     void stop()
  37.     {
  38.         close();
  39.     }
  40. //----------------------------------------------------------------------------------------------------------------------------------
  41.     qint64 readData(char * data, qint64 maxlen)
  42.     {
  43.         QMutexLocker mutexLocker(&m_mutex);
  44.  
  45.         start();
  46.  
  47.         if(m_buffer.isEmpty())
  48.             return 0;
  49.  
  50.         int length = maxlen;
  51.  
  52.         int size = 0;
  53.  
  54.         while (m_buffer.isEmpty() == false) {
  55.             block bl = m_buffer.at(0);
  56.  
  57.             if (bl.len <= length) {
  58.                 memcpy(data+size, bl.ptr, bl.len);
  59.                 m_buffer.removeAt(0);
  60.                 delete [] bl.ptr;
  61.                 length -= bl.len;
  62.                 size += bl.len;
  63.                 continue;
  64.             }
  65.  
  66.             memcpy(data+size, bl.ptr, length);
  67.             bl.len -= length;
  68.             m_buffer[0] = bl;
  69.             memcpy(bl.ptr, bl.ptr+length, bl.len);
  70.             size += length;
  71.             length = 0;
  72.             break;
  73.         }
  74.         if (length > 0)
  75.             memset(data + (maxlen - length), 0xCC, length);
  76.  
  77.         return maxlen;
  78.     }
  79. //----------------------------------------------------------------------------------------------------------------------------------
  80.     qint64 writeData(const char *data, qint64 len)
  81.     {
  82.  
  83.         QMutexLocker mutexLocker(&m_mutex);
  84.  
  85.         start();
  86.  
  87.         char * ptr = new char[len];
  88.         memcpy(ptr,data,len);
  89.         block bl;
  90.         bl.ptr = ptr;
  91.         bl.len = len;
  92.         m_buffer.append(bl);
  93.  
  94.         return len;
  95.     }
  96. //----------------------------------------------------------------------------------------------------------------------------------
  97.     void clear(){
  98.         QMutexLocker mutexLocker(&m_mutex);
  99.  
  100.         for(int i = 0; i<m_buffer.count(); i++)
  101.         {
  102.             block bl = m_buffer.at(i);
  103.  
  104.             delete [] bl.ptr;
  105.         }
  106.  
  107.         m_buffer.clear();
  108.     }
  109. //----------------------------------------------------------------------------------------------------------------------------------
  110. private:
  111.     QList<block> m_buffer;
  112.     QMutex  m_mutex;
  113. };
  114.  
  115. #endif//AUDIOBUFFER_H

Then I do the following thing:

  1. AudioBuffer * m_buf;
  2. QAudioOutput * m_output;
  3.  
  4. m_buf = new AudioBuffer();
  5. m_buf->start();
  6.  
  7. m_output = new QAudioOutput(format);
  8. m_output->start(m_buf);

And later add data in another place:
  1. m_buf->writeData((const char *)data,dataSize);

But after all this manipulations I hear no sound at output.

15 replies

December 19, 2011

Anticross Anticross
Hobby Entomologist
250 posts
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I replace AudioBuffer By new variable QIODevice * m_dev; And do the following declarations

  1.  m_dev = m_output->start();

and replace
  1. m_buf->writeData((const char *)data,dataSize);

by
  1. m_dev->write((const char *)data,dataSize);

And now I get a beautiful noise in output but not that music which I put there. An this noise is interrupt periodically. But it finishes when data transmit finishes. Maybe something wrong with format?

As a source I am using wav file 44100 Hz 16 bit stereo, which i transmit over network an receive data by portions and write it actually here:

  1. m_buf->writeData((const char *)data,dataSize);

So if I use a file to receive this data, and after receiving I open it, it’s contains the music that I transmitt.

Edit: fixed code formatting and merged two posts; Andre

December 19, 2011

Anticross Anticross
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250 posts
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Now I’m using my buffer such as QIODevice

  1. m_buf = (AudioBuffer *)m_output->start();
and get the same. I change the file that I transmit to another one, and notice that I can hear music, but it’s very distorted, and interrupts as I wrote previously. But one more notice that the high freq sounds with low volume hears better than others.

December 19, 2011

Anticross Anticross
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It seems like data sending through RTP is converted to BigEndian format before reaching client. But I find no BigEndian support of playback, so maybe I need to do some fast conversation. Question: How to do that ?

December 19, 2011

Tobias Hunger Tobias Hunger
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RTP defines all values to be transmitted in big-endian, so no surprise there;-)

http://developer.qt.nokia.com/doc/qt-4.8/qtendian.html to the rescue.

December 20, 2011

Anticross Anticross
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OK, thanks. Another question: I have

  1. unsigned char const* data
with size
  1. unsigned dataSize
, qFromBigEndian needs to chose type (qInt16,qInt32,qInt64), and returns value of it’s type, but how can I put this data back into unsigned char const* array with size of dataSize ?

December 20, 2011

Anticross Anticross
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This does not helped:

  1. char * dt = new char[dataSize];
  2. itoa(qFromBigEndian<qint16>(data),dt,2);
  3. m_buf->writeData((const char*)dt,dataSize);
  4. delete dt;

December 20, 2011

Anticross Anticross
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250 posts
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Edited to :

  1. qint16 val = qFromBigEndian<qint16>(data);
  2. uchar* dt = new uchar[dataSize];
  3. qToLittleEndian<qint16>(val,dt);
  4. m_buf->writeData((const char*)dt,dataSize);
  5. delete dt;

But the quality of audio is worse then without conversation.

December 20, 2011

Anticross Anticross
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250 posts
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I write function:

  1. bool SpeakerSink::toLittleEndian( const char * src, int size, int nBits)
  2. {
  3.     if(src == NULL)
  4.         return false;
  5.  
  6.     for (int i = 0; i < size; i+=nBits) {
  7.         qint16 val = qFromBigEndian<qint16>((const uchar*)(src+i));
  8.         qMemCopy((void*)(src+i),&val,nBits);
  9.     }
  10.  
  11.     return true;
  12. }

It solve task of converting from big-endian to little-endian and in headphones I get the same result(I mean sound is recognizable but bad quality) as if my server will transmit data without conversation to big-endian. But sound still distorted and interrupts.

December 20, 2011

Anticross Anticross
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250 posts
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I open VLC player and receive this stream normally, then I look at codec details and see some PCM S16BE. So what is it and can I transform data to play normal PCM on QAudioOutput ? So is it 16-bit Big-endian pcm or something else? What means S ?

December 20, 2011

Anticross Anticross
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I record output of my sound card when receiving stream with sine of 1000 Hz. After opening it in Sound Forge I see pauses in this sine with delays from 5 ms to 25 ms but sine has the same shape(I mean no distortions).

December 20, 2011

Tobias Hunger Tobias Hunger
Mad Scientist
3156 posts
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  • Qt DevNet Moderator

Sorry, no idea what kind of data you send around your network;-)

Why do you have nBits in the toLittleEndian method shown above? Anything but nBits == 2 breaks the method, doesn’t it? The name is rather confusing, too… shouldn’t it at least be nBytes?

December 21, 2011

Anticross Anticross
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250 posts
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You’re right the name must be at least nBytes :) Maybe QAudioOutput reads the buffer faster than it writes by receiving data from network, and I just need to wait some time before playing.

December 21, 2011

Anticross Anticross
Hobby Entomologist
250 posts
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I rewrite my audio buffer class. Now it looks like this:

  1. #ifndef AUDIOBUFFER_H
  2. #define AUDIOBUFFER_H
  3.  
  4. #include <QAudioFormat>
  5. #include <QIODevice>
  6. #include <QMutex>
  7. #include <QDebug>
  8.  
  9. class AudioBuffer : public QIODevice
  10. {
  11.     Q_OBJECT
  12.  
  13. public:
  14. //----------------------------------------------------------------------------------------------------------------------------------
  15.     AudioBuffer(/*const QAudioFormat &format,*/ QObject *parent = NULL, int bufSize = 1400) :   QIODevice(parent)
  16.     {
  17.         m_bufSize = bufSize*4;
  18.  
  19.         m_buffer1 = new const char[m_bufSize];
  20.         m_buffer2 = new const char[m_bufSize];
  21.  
  22.         m_rightOffset = 0;
  23.         m_leftOffset  = 0;
  24.         m_cursor      = 0;
  25.  
  26.         qMemSet((void *)m_buffer1,0,m_bufSize);
  27.  
  28.     }
  29. //----------------------------------------------------------------------------------------------------------------------------------
  30.     ~AudioBuffer()
  31.     {
  32.         delete m_buffer1;
  33.         delete m_buffer2;
  34.     }
  35. //----------------------------------------------------------------------------------------------------------------------------------
  36.     void start()
  37.     {
  38.         if(!isOpen())
  39.             open(QIODevice::ReadWrite);
  40.     }
  41. //----------------------------------------------------------------------------------------------------------------------------------
  42.     void stop()
  43.     {
  44.         close();
  45.     }
  46. //----------------------------------------------------------------------------------------------------------------------------------
  47.     qint64 readData(char * data, qint64 len)
  48.     {
  49.         int free2end = m_bufSize-m_cursor;
  50.  
  51.         if(len <= free2end){
  52.             qMemCopy(data,m_buffer1+m_cursor,len);
  53.  
  54.             m_rightOffset += len;
  55.             m_cursor += len;
  56.  
  57.             return len;
  58.         }
  59.         else
  60.         {
  61.             qMemCopy(data,m_buffer1+m_cursor,free2end);
  62.  
  63.             m_cursor = 0;
  64.  
  65.             qMemCopy(data+free2end,m_buffer1,len-free2end);
  66.  
  67.             m_rightOffset = len-free2end;
  68.             m_leftOffset = 0;
  69.             m_cursor += m_rightOffset;
  70.  
  71.             return len;
  72.         }
  73.  
  74.         return 0;
  75.     }
  76. //----------------------------------------------------------------------------------------------------------------------------------
  77.     qint64 writeData(const char *data, qint64 len)
  78.     {
  79.         int free2end   = m_bufSize-m_rightOffset;
  80.  
  81.         if(len <= free2end) // if we don't reach end of buffer
  82.         {
  83.             qMemCopy((void*)(m_buffer1+m_rightOffset),data,len);
  84.             m_rightOffset += len;
  85.  
  86.             qDebug() << m_buffer1;
  87.  
  88.             return len;
  89.         }
  90.         else if(len <= (m_leftOffset+free2end))
  91.         {
  92.             qMemCopy((void*)(m_buffer1+m_rightOffset),data,free2end); //write to end
  93.             m_leftOffset = len-free2end; // need to write more from source and set new left offset
  94.             qMemCopy((void*)m_buffer1,data+free2end,m_leftOffset); //write lefted part
  95.             m_rightOffset = m_leftOffset; // set new right offset value
  96.             m_leftOffset  = 0; // set new left offset value
  97.  
  98.             qDebug() << m_buffer1;
  99.  
  100.             return len;
  101.         }
  102.         else
  103.         {
  104.             qMemCopy((void*)(m_buffer1+m_rightOffset),data,free2end); //write to end
  105.             m_rightOffset += len-free2end; // need to write more from source
  106.  
  107.             len -= free2end;
  108.  
  109.             qMemCopy((void*)m_buffer1,data+free2end,m_leftOffset); //write lefted part
  110.             m_rightOffset = 0; // set new right offset value
  111.  
  112.             len -= m_leftOffset;
  113.  
  114.             m_leftOffset = 0;
  115.  
  116.             qDebug() << m_buffer1;
  117.  
  118.             return len;
  119.         }
  120.  
  121.         return 0;
  122.     }
  123. //----------------------------------------------------------------------------------------------------------------------------------
  124. private:
  125.     const char * m_buffer1;
  126.     const char * m_buffer2;
  127.     int          m_rightOffset;
  128.     int          m_leftOffset;
  129.     int          m_cursor;
  130.     int          m_bufSize;
  131. };
  132.  
  133. #endif//AUDIOBUFFER_H

And now I’m using it like this:
  1. m_output->start(m_buf);

and it enters write data functions, but doesn’t reads data. So question: How QAudioOutput asks for the data to play from QIODevice ? Is it call readData function or not ? And one more question: Is it possible to play rtsp stream using Phonon ?

December 21, 2011

Anticross Anticross
Hobby Entomologist
250 posts
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One more question whats the main difference between push and pull mode of playing ?

December 29, 2011

Anticross Anticross
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250 posts
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Interesting thing: when I play 22050 Hz 16 bit 2 channels audio stream – it plays normally without interruptions, but when playing 44100 Hz 16 bit stereo – not. If I open same stream(44 kHz) in VLC player or any other it plays normally without interruptions.

 
  ‹‹ What may be the cause of following error?      QT 4.7 cannot receive multi-touch events. ››

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