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音频处理中，有时不同的编解码器支持的音频格式不一样，原始采样的音频数据可能没法直接直接为编解码器支持，如FFMPEG编码MP3格式的音频，就要求样本采用AV_SAMPLE_FMT_S16P格式保存。

1、如果PCM文件采用交叉存储方式，视频帧的概念可能没什么影响，因为数据都是LRLRLR...LR方式；2、如果采用平行存储方式，L...LR...RL...LR...R,一帧必须按照指定的数据读取了,如MP3读取一帧需要读取1152*2(通道数)个样本，然后前1152为左声道，后1152为右声道。

/*******************************************************************************Copyright (c) wubihe Tech. Co., Ltd. All rights reserved.--------------------------------------------------------------------------------Date Created:	2014-10-25Author:			wubihe QQ:1269122125 Email:1269122125@qq.comDescription:	代码实现音频重采样 把交叉存储的双声道立体声转换成平行存储的双声道				立体声--------------------------------------------------------------------------------Modification HistoryDATE          AUTHOR          DESCRIPTION--------------------------------------------------------------------------------********************************************************************************/#include 
   
     #define __STDC_CONSTANT_MACROS#include "libavcodec/avcodec.h"#include "libavformat/avformat.h"#include "libswresample/swresample.h"  int main(){
    	static char*pFormatName[]=	{
   		"FMT_U8","FMT_S16","FMT_S32","FMT_FLT","FMT_DBL",		"FMT_U8P","FMT_S16P","FMT_S32P","FMT_FLTP","FMT_DBLP"	};  	//原始PCM文件	FILE *pInputFile = fopen("huangdun_r48000_FMT_S16_c2.pcm", "rb");	uint64_t iInputLayout				= AV_CH_LAYOUT_STEREO;	int      iInputChans				= av_get_channel_layout_nb_channels(iInputLayout);	AVSampleFormat eInputSampleFormat   = AV_SAMPLE_FMT_S16;	int	     iInputSampleRate			= 48000; 	//转换后PCM文件	uint64_t iOutputLayout				= AV_CH_LAYOUT_STEREO;	int      iOutputChans				= av_get_channel_layout_nb_channels(iOutputLayout);	AVSampleFormat eOutputSampleFormat  = AV_SAMPLE_FMT_S16P;	int	     iOutputSampleRate			= 48000; 	bool bOutPutPlaner=true; 	char szOutFileName[256]={
   0};	sprintf(szOutFileName,"huangdun_r%d_%s_c%d.pcm",iOutputSampleRate,pFormatName[eOutputSampleFormat],iOutputChans);		FILE *pOutputFile = fopen(szOutFileName, "wb"); 	//初始化转换上下文	SwrContext *pSwrCtx = swr_alloc_set_opts(NULL,iOutputLayout, eOutputSampleFormat, iOutputSampleRate,		iInputLayout,eInputSampleFormat , iInputSampleRate,0, NULL);	swr_init(pSwrCtx); 	//1帧数据样本数	int iFrameSamples = 1024; 	//保存转换后的数据	/*uint8_t **ppConvertData = (uint8_t**)calloc(iOutputChans,sizeof(*ppConvertData));	int iConvertLineSize = 0;	int iConvertDataSize = av_samples_alloc(ppConvertData, &iConvertLineSize,iOutputChans, iFrameSamples,eOutputSampleFormat, 0);*/ 	//音频处理是以帧为单位处理的	//分配存储原始数据内存空间 	int iRawLineSize = 0;	int iRawBuffSize  = av_samples_get_buffer_size(&iRawLineSize, iInputChans, iFrameSamples, eInputSampleFormat, 0);	uint8_t *pRawBuff = (uint8_t *)av_malloc(iRawBuffSize); 	//原始数据保存在AVFrame结构体中	AVFrame* pRawframe = av_frame_alloc(); 	pRawframe->nb_samples	= iFrameSamples;	pRawframe->format		= eInputSampleFormat;	pRawframe->channels     = iInputChans; 	//把分配内存挂到AVFrame结构体中	avcodec_fill_audio_frame(pRawframe, iInputChans, eInputSampleFormat, (const uint8_t*)pRawBuff, iRawBuffSize, 0);  	// 计算并申请一段buf用于存放数据	int iConvertLineSize = 0;	int iConvertBuffSize  = av_samples_get_buffer_size(&iConvertLineSize, iOutputChans, iFrameSamples, eOutputSampleFormat, 0);	uint8_t *pConvertBuff = (uint8_t *)av_malloc(iConvertBuffSize); 	//转换后数据保存在AVFrame结构体中	AVFrame* pConvertframe = av_frame_alloc();	pConvertframe->nb_samples	= iFrameSamples;	pConvertframe->format		= eOutputSampleFormat;	pConvertframe->channels     = iOutputChans; 	avcodec_fill_audio_frame(pConvertframe, iOutputChans, eOutputSampleFormat, (const uint8_t*)pConvertBuff, iConvertBuffSize, 0);	//将数据buf给avframe的date*       如果需要平面音频，则分配AVFrame extended_data通道指针。  	int iFrameNum =0;		//读取一帧音频数据	int iRealRead = fread(pRawBuff, 1, iRawBuffSize, pInputFile);	while(iRealRead>0)	{
   		//完成音频帧转换		swr_convert(pSwrCtx, (uint8_t**)pConvertframe->data, iFrameSamples ,(const uint8_t**)pRawframe->data, iFrameSamples );		 		if(bOutPutPlaner)		{
   			//只保存一个通道数据 便于分析 因为PCM工具不支持这种平行存储方式数据查看			//一般情况平行存储方式pConvertframe->data[i]为i声道数据   pConvertframe->linesize[i]为i声道长度,			//但是音频各个声道的数据长度是相同的，所以只有pConvertframe->linesize[0]表示长度，			//其他pConvertframe->linesize[1]==0			fwrite(pConvertframe->data[0],pConvertframe->linesize[0],1,pOutputFile);		}				printf("Convert Frame :%d\n",++iFrameNum);		 		iRealRead = fread(pRawBuff, 1, iRawBuffSize, pInputFile);	} 	fclose(pInputFile);	fclose(pOutputFile); 	av_free(pRawBuff);	av_free(pConvertBuff); 	swr_free(&pSwrCtx); 	printf("Convert Success!!\n");	getchar();	return 0; }
   

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