ffmpeg库G726编解码实例

ffmpeg g726编码器：AV_CODEC_ID_ADPCM_G726

ffmpeg g726解码器包括：AV_CODEC_ID_ADPCM_G726、AV_CODEC_ID_ADPCM_G726LE

 

AV_CODEC_ID_ADPCM_G726，无法指定码流，默认是16kps；AV_CODEC_ID_ADPCM_G726LE，可以指导码流，AVCodecContext中的bits_per_coded_sample:表示编码压缩bit值与采样率的bit值之比。如果为g726音频时，表示g726码流压缩与采样率比值。比如kbps码流压缩比为：k/8k = 5，kbps码流压缩比为k/8k = 2。

 //编码

extern "C"{#include "libavcodec/avcodec.h"#include "libavformat/avformat.h"#include "libavutil/frame.h"#include "libswscale/swscale.h"#include "libavutil/imgutils.h"}//链接ffmpeg lib库//pcm to g726AVCodec *codec;AVCodecContext *c= NULL;AVPacket avpkt;AVFrame *decoded_frame = NULL;/* register all the codecs */avcodec_register_all();av_init_packet(&avpkt);avpkt.data = NULL;avpkt.size = 0;/* find the mpeg audio decoder */codec = avcodec_find_encoder(AV_CODEC_ID_ADPCM_G726);if (!codec) {fprintf(stderr, "codec not found\n");return;}c = avcodec_alloc_context3(codec);//put sample parameters c->bits_per_coded_sample = 2;c->bit_rate = 16000;    //c->sample_rate = 8000;    //采样率c->channels = 1;     //通道数c->sample_fmt = AV_SAMPLE_FMT_S16;//采样位数/* open it */int iRet = avcodec_open2(c, codec,NULL);if ( iRet < 0 ) {fprintf(stderr, "could not open codec\n");return;}CString filePath = "";CString newlFilePath = "";char szFilter[] = {"Pcm Files (*.pcm)|*.pcm||"};CFileDialog dlg(TRUE,NULL,NULL,OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT,szFilter,NULL);if(dlg.DoModal() == IDOK){filePath = dlg.GetPathName();newlFilePath = filePath;newlFilePath.Replace(".pcm","_ff.g726");FILE * fpSrc = fopen(filePath.GetBuffer(filePath.GetLength()),"rb");FILE * fpDst = fopen(newlFilePath.GetBuffer(newlFilePath.GetLength()),"wb+");char szData[320] = {0};char szOutData[200] = {0};int  nDataLen = 320;int  nOutDataLen = 200;int  nReadedSize = 0;int  ret = 0;if(fpSrc != NULL){while(TRUE){nReadedSize = fread(szData,sizeof(char),nDataLen,fpSrc);if(nReadedSize < nDataLen){break;}if (!decoded_frame) {if (!(decoded_frame = avcodec_alloc_frame())) {return;}} else{avcodec_get_frame_defaults(decoded_frame);}decoded_frame->nb_samples = nReadedSize/(c->channels*av_get_bytes_per_sample(c->sample_fmt));ret = avcodec_fill_audio_frame(decoded_frame, c->channels, c->sample_fmt, (unsigned char *)szData,nReadedSize, 1);if (ret < 0) {return;}int got_packet = 0;if (avcodec_encode_audio2(c, &avpkt, decoded_frame, &got_packet) < 0) {return;}if (got_packet) {int iiiii = fwrite( avpkt.data, 1, avpkt.size, fpDst );}}fclose(fpSrc);fclose(fpDst);}}

//解码

extern "C"{#include "libavcodec/avcodec.h"#include "libavformat/avformat.h"#include "libavutil/frame.h"#include "libswscale/swscale.h"#include "libavutil/imgutils.h"}//链接ffmpeg lib库//g726 to pcmAVCodec *codec;AVCodecContext *c= NULL;AVPacket avpkt;AVFrame *decoded_frame = NULL;avcodec_register_all();av_init_packet(&avpkt);/* find the mpeg audio decoder */codec = avcodec_find_decoder(AV_CODEC_ID_ADPCM_G726);if (!codec) {fprintf(stderr, "codec not found\n");return;}c = avcodec_alloc_context3(codec);//采样率= 8000 每个采样用的bit数= 16 通道数= 1c->bits_per_coded_sample = 2;   //g726压缩比为8:1 编码前采样用bit数为那么编码后应该占/8 = 2c->channels = 1;c->sample_fmt = AV_SAMPLE_FMT_S16;c->sample_rate = 8000;c->codec_type = AVMEDIA_TYPE_AUDIO;c->bit_rate = 16000;int iRet = avcodec_open2(c, codec,NULL);if ( iRet < 0 ) {fprintf(stderr, "could not open codec\n");return;}CString filePath = "";CString newlFilePath = "";char szFilter[] = {"g726 Files (*.g726)|*.g726||"};CFileDialog dlg(TRUE,NULL,NULL,OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT,szFilter,NULL);if(dlg.DoModal() == IDOK){filePath = dlg.GetPathName();newlFilePath = filePath;newlFilePath.Replace(".g726",".pcm");BOOL bRet = 0;FILE * fpSrc = fopen(filePath.GetBuffer(filePath.GetLength()),"rb");FILE * fpDst = fopen(newlFilePath.GetBuffer(newlFilePath.GetLength()),"wb+");char szData[100] = {0};char szOutData[320] = {0};int  nDataLen = c->bits_per_coded_sample*20;int  nOutDataLen = 320;int  nReadedSize = 0;if(fpSrc != NULL){while(TRUE){nDataLen = 40;nReadedSize = fread(szData,sizeof(char),nDataLen,fpSrc);if(nReadedSize < nDataLen){break;}avpkt.data = (uint8_t *)szData;avpkt.size = nDataLen;int got_frame = 0;if (!decoded_frame) {if (!(decoded_frame = avcodec_alloc_frame())) {return;}} else{avcodec_get_frame_defaults(decoded_frame);}int len = avcodec_decode_audio4(c, decoded_frame, &got_frame, &avpkt);if (len < 0) {return;}if (got_frame) {/* if a frame has been decoded, output it */int data_size = av_samples_get_buffer_size(NULL, c->channels,decoded_frame->nb_samples,c->sample_fmt, 1);fwrite(decoded_frame->data[0], 1, data_size, fpDst);}}fclose(fpSrc);fclose(fpDst);avcodec_close(c);av_free(c);av_free(decoded_frame);}}

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