QProcess 调用 ffmpeg来处理音频

项目场景：

在文章 qt 实现音视频的分贝检测系统中，实现的是边播放变解析音频数据来统计音频的分贝大小，并不满足实际项目的需求，有的视频声音正常，有的视频声音就偏低，即使放到最大音量声音也是比较小，本文的目的是直接通过对本地视频进行检测，拿出关键指标，来进行对音频处理

关键依赖：ffmpeg

因为依赖于ffmpeg的能力，所以第一步要安装ffmpeg环境，自行百度

步骤1，检测max_volume 值是否小于0dB

 ffmpeg -i 1.mp3  -filter_complex volumedetect -c:v copy -f null /dev/null

其中检测的关键指标就是 max_volume, 本次检测和处理的目标就是把 max_volume的值给提高到0dB;

步骤2，如何区分是音频文件还是视频文件

可以有多种方法，1可以通过后缀名来区分； 2 因为代码是用qt写的，可以用qt来实现，代码如下

QFileInfo f(“1.mp3”);
if(f.completeSuffix() == "mp3" || f.completeSuffix() == "aac" || 
f.completeSuffix() == "amr" || f.completeSuffix() == "wav" || f.completeSuffix() == "wma" )

QMediaPlayer p;
p.audioAvailable()；

步骤3，处理音频，使max_volume的值接近0dB

音频文件用以下指令

ffmpeg -i 1.mp3-af  "volume=5.8dB"  out.mp3

如果是视频文件，用以下指令：（保持视频信息不变，当然还设计到音频的编码格式）

ffmpeg -i 1.mp3-af  "volume=5.8dB" -c:v copy -c:a aac out.mp3

输出如下

程序设计思路

dbdetectthread.h

#ifndef DBDETECTTHREAD_H
#define DBDETECTTHREAD_H

#include <QObject>
#include <QThread>
#include <QProcess>
#include <QStringList>

class DbDetectThread : public QThread
{
    Q_OBJECT
public:
    explicit DbDetectThread(QObject *parent = nullptr);
    void setList(const QStringList &list);
    virtual void run();
signals:
    void sigPath(const QString &p, float db);
    void sigMsg(const QString &p);
    void sigEnd();

public slots:
    void readStandardOutput();
    void readStandardError();
    void processFinished(int exitCode, QProcess::ExitStatus exitStatus);
    void threadFinished(); //线程退出

private:
    QProcess *pCmdProcess;
    QStringList pathlist;
    QString curFile;
};

#endif // DBDETECTTHREAD_H

dbdetectthread.cpp

#include "dbdetectthread.h"
#include <QDebug>
DbDetectThread::DbDetectThread(QObject *parent)
    : QThread{parent}
{
    qRegisterMetaType<QProcess::ExitStatus>("QProcess::ExitStatus");
}

void DbDetectThread::setList(const QStringList &list)
{
    pathlist = list;
}

//ffmpeg -i 2.wav -filter_complex volumedetect -c:v copy -f null /dev/null

//需要计算分贝相差值
//ffmpeg  -i 2.wav -filter:a "volume=80dB" output2.wav

void DbDetectThread::run()
{
    pCmdProcess = new QProcess();    //不要加this
    connect(pCmdProcess, &QProcess::readyReadStandardOutput, this, &DbDetectThread::readStandardOutput);
    connect(pCmdProcess, &QProcess::readyReadStandardError, this, &DbDetectThread::readStandardError);
    connect(pCmdProcess, QOverload<int , QProcess::ExitStatus >::of(&QProcess::finished), this, &DbDetectThread::processFinished);
    connect(this, &QThread::finished, this, &DbDetectThread::threadFinished);

    QStringList arguments;
    //arguments << "-i" << "C:/Users/wmm/Desktop/DbDetect/voice/input.mp4" << "-c:v" << "h264" << "-c:a" << "aac" << "C:/Users/wmm/Desktop/DbDetect/voice/output.mp4";
    //arguments << "-i" << "input.mp4" << "-c:v" << "h264" << "-c:a" << "aac" << "output.mp4";
    //arguments << "-i" << p << "-filter_complex"<< "volumedetect" <<  "-c:v" << "copy" << "-f" << "null" << "/dev/null";
    //QString cmd = QString("ffmpeg -i %1 -filter_complex volumedetect -c:v copy -f null /dev/null").arg(p);

    //QString cmd = QString("ffmpeg -i C:/Users/wmm/Desktop/DbDetect/voice/input.mp4 -filter_complex volumedetect -c:v copy -f null /dev/null");
    //QString cmd = "ping www.baidu.com -w 500";
    //QString result;
    foreach(auto p, pathlist)
    {
        curFile = p;
        qDebug() << "start detect " << curFile;
        QString cmd = QString("ffmpeg -i %1 -filter_complex volumedetect -c:v copy -f null /dev/null").arg(p);
        pCmdProcess->start(cmd/*,arguments*/);
        pCmdProcess->waitForFinished();
        sleep(1);
    }

}

void DbDetectThread::readStandardOutput() {
    qDebug() << "Standard output: " << pCmdProcess->readAllStandardOutput();
}

void DbDetectThread::readStandardError() {
    QString errorMessage = QString::fromUtf8(pCmdProcess->readAllStandardError());
    QStringList errlist = errorMessage.split("\r\n");
    //qDebug() << errlist.size();
    //qDebug() << errlist;

//    float num = 3.1415926;
//    QString str = QString::number(num, 'f', 2);

    foreach (auto p, errlist) {
        if(p.contains("max_volume"))
        {
            qDebug() << p;
            int pos = p.indexOf("max_volume");
            int pos2 = p.indexOf("dB",pos);
            QString val = p.mid(pos+11,pos2-11-pos);

            qDebug() <<val;
            float fval = val.toFloat();
            qDebug() << fval;

            if(fval <0)
            {
                qDebug() << "小于0";
                emit sigPath(curFile,fval);
            }
            else
            {
                qDebug() << "不小于0";
            }
        }
    }
        // 对 errorMessage 进行解析和处理...
    //qDebug() << "Standard error: " << pCmdProcess->readAllStandardError();
}

void DbDetectThread::processFinished(int exitCode, QProcess::ExitStatus exitStatus) {
    qDebug() << "Process finished with exit code" << exitCode << "and exit status" << exitStatus << ((QProcess*)QObject::sender())->arguments();
    emit sigMsg(QString("%1 检测完成，exitCode = %2, exitStatus = %3 ").arg(curFile).arg(exitCode).arg(exitStatus));
}

void DbDetectThread::threadFinished()
{
    qDebug() << __func__;
    emit sigEnd();
    pCmdProcess->deleteLater();
}

dbprocessthread.h

#ifndef DBPROCESSTHREAD_H
#define DBPROCESSTHREAD_H

#include <QObject>
#include <QThread>
#include <QProcess>
#include <QMap>
#include <QMediaPlayer>
class DbProcessThread : public QThread
{
    Q_OBJECT
public:
    explicit DbProcessThread(QObject *parent = nullptr);

    void setOutputDir(const QString &dir);
    void setMap(const QMap<QString,float> &map);
    virtual void run();
signals:
    void sigPath(const QString &p, float db);
    void sigMsg(const QString &p);
    void sigEnd();

public slots:
    void readStandardOutput();
    void readStandardError();
    void processFinished(int exitCode, QProcess::ExitStatus exitStatus);
    void threadFinished(); //线程退出

private:
    QProcess *pCmdProcess;
    QMediaPlayer  mediaPlayer;
    QMap<QString,float> m_needProcessMap;
    QString m_outputDir;
    QString m_curSrcFile;
    QString m_curDesFile;
};

#endif // DBPROCESSTHREAD_H

dbprocessthread.cpp

#include "dbprocessthread.h"
#include <QDebug>
#include <QFileInfo>
DbProcessThread::DbProcessThread(QObject *parent)
    : QThread{parent}
{

}

void DbProcessThread::setOutputDir(const QString &dir)
{
    m_outputDir = dir;
}

void DbProcessThread::setMap(const QMap<QString, float> &map)
{
    m_needProcessMap = map;
}

void DbProcessThread::run()
{
    pCmdProcess = new QProcess();    //不要加this
    connect(pCmdProcess, &QProcess::readyReadStandardOutput, this, &DbProcessThread::readStandardOutput);
    connect(pCmdProcess, &QProcess::readyReadStandardError, this, &DbProcessThread::readStandardError);
    connect(pCmdProcess, QOverload<int , QProcess::ExitStatus >::of(&QProcess::finished), this, &DbProcessThread::processFinished);
    connect(this, &QThread::finished, this, &DbProcessThread::threadFinished);

    QMapIterator<QString, float> i(m_needProcessMap);
    while (i.hasNext()) {
        i.next();
        QFileInfo f(i.key());
        qDebug() << f.fileName() << m_outputDir+"/" + f.fileName();
        m_curSrcFile = i.key();
        m_curDesFile = m_outputDir+"/" + f.fileName();
        QStringList arguments;
        //arguments << "-i" << i.key() << "-c:v" << "h264" << "-c:a" << "aac" << m_outputDir+"/" + f.fileName();
        arguments << "-i" << i.key() << "-af" << QString("volume=%1dB").arg(qAbs(i.value())) << "-c:v copy" << " -c:a aac "  << m_outputDir+"/" + f.fileName();
        qDebug() << arguments;
        emit sigMsg(QString("正在处理...%1").arg(m_curSrcFile));

        if(f.completeSuffix() == "mp3" || f.completeSuffix() == "aac" || f.completeSuffix() == "amr" || f.completeSuffix() == "wav"\
                 || f.completeSuffix() == "wma" )
        {
            pCmdProcess->start(QString("ffmpeg -i %1 -af \"volume=%2dB\"  %3").arg(i.key()).arg(qAbs(i.value())).arg(m_outputDir+"/" + f.fileName())/*,arguments*/);
        }
        else {
            pCmdProcess->start(QString("ffmpeg -i %1 -af \"volume=%2dB\" -c:v copy  %3").arg(i.key()).arg(qAbs(i.value())).arg(m_outputDir+"/" + f.fileName())/*,arguments*/);
        }

        //pCmdProcess->start(QString("ffmpeg -i %1 -af \"volume=%2dB\" -c:v copy -c:a aac %3").arg(i.key()).arg(qAbs(i.value())).arg(m_outputDir+"/" + f.fileName())/*,arguments*/);
        pCmdProcess->waitForFinished();
        msleep(500);
    }

}

void DbProcessThread::readStandardOutput() {
    qDebug() << "Standard output: " << pCmdProcess->readAllStandardOutput();
}

void DbProcessThread::readStandardError() {
    qDebug() << "Standard error: " << pCmdProcess->readAllStandardError();
}

void DbProcessThread::processFinished(int exitCode, QProcess::ExitStatus exitStatus) {
    qDebug() << "Process finished with exit code" << exitCode << "and exit status" << exitStatus << ((QProcess*)QObject::sender())->arguments();
    emit sigMsg(QString("%1 处理完成,文件保存为%2，exitCode = %3, exitStatus = %4 ").arg(m_curSrcFile).arg(m_curDesFile).arg(exitCode).arg(exitStatus));
}

void DbProcessThread::threadFinished()
{
    qDebug() << __func__;
    emit sigEnd();
    pCmdProcess->deleteLater();
}

效果如图：

代码上传到此 https://download.csdn.net/download/u011942101/88299291