ffmpeg重采样指的是可以将一个固定频率的音频转换为任意格式的音频，比如改变音频的采样率或者声道，这种操作简称为重采样。但是在重采样的过程中也会有一些数据丢失的过程，主要原因是在采样会会进行向上对齐，所以会出现转换后大小不一致的情况

在重采样的过程中，主要通过两个容器来互相交换数据来达到数据转换的效果，其中创建容器的方法为：

//返回值小于0代表创建失败
int av_samples_alloc_array_and_samples(uint8_t ***audio_data, int *linesize, int nb_channels,int nb_samples, enum AVSampleFormat sample_fmt, int align);

在进行重采样操作时，另开一个线程来完成此工作

void Audiothread::run()
{ResampleAudioSpec in,out;//44100-s16le-2in.FileName = "D:/ffmpeg/ffm07_31_21_57_24.pcm";out.FileName = "D:/ffmpeg/4800_f32le_1.pcm";//初始化重采样上下文int ret = 0;//输入参数in.SamPleFmt = AV_SAMPLE_FMT_S16;//f32lein.SampleRate = 44100;in.ChLayout = AV_CH_LAYOUT_STEREO;//2声道//输出参数out.SamPleFmt = AV_SAMPLE_FMT_FLT;out.SampleRate = 48000;out.ChLayout = AV_CH_LAYOUT_MONO;//1声道ffmpegs::resampleAudio(in,out);
}

#include "ffmpegs.h"
#include <QDebug>
#include <QFile>
extern "C" {
//
#include <libswresample/swresample.h>
// 工具相关API（比如错误处理）
#include <libavutil/avutil.h>
}#define ERROR_BUF(ret) \char errbuf[1024]; \av_strerror(ret,errbuf,sizeof(errbuf));
ffmpegs::ffmpegs()
{}void ffmpegs::resampleAudio(ResampleAudioSpec& in, ResampleAudioSpec& out)
{resampleAudio(in.FileName,in.SampleRate,in.SamPleFmt,in.ChLayout,out.FileName,out.SampleRate,out.SamPleFmt,out.ChLayout);
}void ffmpegs::resampleAudio(const char *inFilename,int inSamplesRate,AVSampleFormat inSamplesFmt,int inChLayout,const char *outFilename,int outSampleRate,AVSampleFormat outSampleFmt1,int outChLayout)
{//44100-s16le-2QFile inFile(inFilename);QFile outFile(outFilename);//创建输入缓冲区//指向缓冲区的指针uint8_t **inData = nullptr;//缓冲区大小int inLinesize = 0;//声道数int inChs = av_get_channel_layout_nb_channels(inChLayout);//一个样本大小int inBytesPerSample = inChs * av_get_bytes_per_sample(inSamplesFmt);//缓冲区的样本数量int inSamples = 1024;//读取文件的数据大小int len = 0;//创建输出缓冲区//指向缓冲区的指针uint8_t **outData = nullptr;//缓冲区大小int outLinesize = 0;//声道数int outChs = av_get_channel_layout_nb_channels(inChLayout);//一个样本大小int outBytesPerSample = outChs * av_get_bytes_per_sample(outSampleFmt1);//缓冲区的样本数量int outSample = av_rescale_rnd(outSampleRate,inSamples,inSamplesRate,AV_ROUND_UP);//outSample = outSampleRate * inSamples / inSamplesRate//例如b[i] = av_rescale_rnd(a[i], 2, 1, AV_ROUND_NEAR_INF); // 缩放因子为2:1，所以b[i] = 2 * a[i]/*inSamplesRate    inSampless------------ =  ---------outSampleRate   outSamples*///返回结果int ret = 0;int isSamples = 0;//创建重采样上下文SwrContext *ctx = swr_alloc_set_opts(nullptr,//输出参数outChLayout,outSampleFmt1,outSampleRate,//输入参数inChLayout,inSamplesFmt,inSamplesRate,0,nullptr);if(!ctx){qDebug() << "swr_alloc_set_opts----error";return;}//初始化重采样上下文ret = swr_init(ctx);if(ret < 0){ERROR_BUF(ret);qDebug() << "swr_init" << errbuf;goto end;return;}//创建输出缓冲区//ret = 返回几个字节ret = av_samples_alloc_array_and_samples(&outData,&outLinesize,outChs,outSample,outSampleFmt1,1);if(ret < 0){ERROR_BUF(ret);qDebug() << "av_samples_alloc_array_and_samples error: " << errbuf;goto end;}//创建输入缓冲区//ret = 返回几个字节ret = av_samples_alloc_array_and_samples(&inData,&inLinesize,inChs,inSamples,inSamplesFmt,1);if(ret < 0){ERROR_BUF(ret);qDebug() << "av_samples_alloc_array_and_samples error: " << errbuf;goto end;}//打开文件if(!inFile.open(QFile::ReadOnly)){qDebug() << "打开文件失败:" << inFilename;goto end;}if(!outFile.open(QFile::WriteOnly)){qDebug() << "打开文件失败:" << outFilename;goto end;}//读取文件数据while((len = inFile.read((char*) inData[0],inLinesize)) > 0){//读取的样本数量isSamples = len / inBytesPerSample;//重采样(返回值转换后的样本数量)ret = swr_convert(ctx,outData,outSample,(const uint8_t **)inData,isSamples);if(ret < 0){ERROR_BUF(ret);qDebug() << "swr_convert error" << errbuf;goto end;}int size = av_samples_get_buffer_size(nullptr,outChs,ret,outSampleFmt1,1);//size == ret * outBytesPerSample//将转换后的数据写入输出文件中//outFile.write((char*) outData[0],ret * outBytesPerSample);outFile.write((char*) outData[0],size);}//检查一下输出缓冲区是否还有残留的样本（已经重采样过的，转换过的）while((ret = swr_convert(ctx,outData,outSample,nullptr,0)) > 0){//将转换后的数据写入输出文件中outFile.write((char*) outData[0],ret * outBytesPerSample);}
end://释放资源//关闭文件inFile.close();outFile.close();//释放重采样上下文swr_free(&ctx);//释放输出缓冲区av_free(&outData[0]);//释放输入缓冲区av_free(&inData[0]);return;//释放资源//释放重采样上下文swr_free(&ctx);
}