Qt调用aplay播放PCM

今天接到个任务，让我用Qt播放PCM，这个简单，随便一百度就有了。

#ifndef PLAYPCM_H
#define PLAYPCM_H

#include <QObject>
#include <QAudioOutput>
#include <QIODevice>

class PlayPCM : public QObject
{
    Q_OBJECT
    QAudioOutput *audioOutput = nullptr;
    QIODevice *streamOut = nullptr;
#endif

public:
    explicit PlayPCM(int sampleRate = 44100, int channels = 2, int sampleSize = 16, QObject *parent = nullptr);
    ~PlayPCM();
signals:

public slots:
    void writePCM(QByteArray array);
};
#endif // PLAYPCM_H

#include "playpcm.h"
#include <QDebug>
#include <QAudioFormat>
#include <QAudioDeviceInfo>

PlayPCM::PlayPCM(int sampleRate, int channels, int sampleSize, QObject *parent) : QObject(parent)
{
    //设置采样格式
    QAudioFormat audioFormat;
    //设置采样率
    audioFormat.setSampleRate(sampleRate);
    //设置通道数
    audioFormat.setChannelCount(channels);
    //设置采样大小，一般为8位或16位
    audioFormat.setSampleSize(sampleSize);
    //设置编码方式
    audioFormat.setCodec("audio/pcm");
    //设置字节序
    audioFormat.setByteOrder(QAudioFormat::LittleEndian);
    //设置样本数据类型
    audioFormat.setSampleType(QAudioFormat::UnSignedInt);
    //音频设备信息

    QList<QAudioDeviceInfo> list = QAudioDeviceInfo::availableDevices(QAudio::AudioOutput);
    foreach (QAudioDeviceInfo info, list) {
        if (info.isFormatSupported(audioFormat)) {
            audioOutput = new QAudioOutput(audioFormat, this);
            streamOut = audioOutput->start();
            break;
        }
    }
}

PlayPCM::~PlayPCM()
{
    delete audioOutput;
    audioOutput = nullptr;
    streamOut = nullptr;
}

void PlayPCM::writePCM(QByteArray array)
{
    if (streamOut)
        streamOut->write(array);
}

#endif

不过在运行的时候出了问题

ALSA lib pcm_hw.c:1788:(_snd_pcm_hw_open) Unknown field slave

嘶~ 好像是alsa源码出了问题，但是又不想去看源码......

我记得arm板上有了aplay这个程序，试试它能不能播WAV，可以的话就参考它的源码自己写一个PCM播放

# aplay -D hw:0,0 a.wav
Playing WAVE 'a.wav' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

可以！ 再把WAV掐掉头变成PCM

# aplay -D hw:0,0 a.pcm
Playing raw data 'a.pcm' : Unsigned 8 bit, Rate 8000 Hz, Mono
aplay: set_params:1297: Sample format non available
Available formats:
- S16_LE
- S24_LE

......看来需要指定参数

aplay -D hw:0,0 -r 44100 -c 2 -f s16 a.pcm
Playing raw data 'a.pcm' : Signed 16 bit Little Endian, Rate 44100 Hz, Stereo

可以播了，去参考参考(复制)aplay的源码，然后发现了aplay输入源可以是 stdin，这就舒服了啊，这下连代码都不用参考了

#ifndef PLAYPCM_H
#define PLAYPCM_H

#include <QObject>
#include <QProcess>

class PlayPCM : public QObject
{
    Q_OBJECT
    QProcess process;

public:
    explicit PlayPCM(int sampleRate = 44100, int channels = 2, int sampleSize = 16, QObject *parent = nullptr);
    ~PlayPCM();
signals:

public slots:
    void writePCM(QByteArray array);
};

#endif // PLAYPCM_H

#include "playpcm.h"
#include <QDebug>
PlayPCM::PlayPCM(int sampleRate, int channels, int sampleSize, QObject *parent) : QObject(parent)
{
    char cmd[128];
    sprintf(cmd, "aplay -D hw:0,0 -r %d -c %d -f s%d", sampleRate, channels, sampleSize);
    process.start(cmd);
    if (process.waitForStarted()){
        //qDebug() << "PCM player is ready.";
    }
}

PlayPCM::~PlayPCM()
{
    process.kill();
}

void PlayPCM::writePCM(QByteArray array)
{
    if (process.isOpen())
        process.write(array);
}

参考：
一定要仔细看的help

aplay -h