代码和上篇几乎一模一样，只需将输出文件的后缀改为mp3即可。

目录

程序源码

看到几篇不错的博文

程序源码

/****本程序实现了音频PCM采样数据编码为压缩码流（MP3，WMA，AAC等）。**/#include <stdio.h>#define __STDC_CONSTANT_MACROSextern "C"{#include "libavformat/avformat.h"#include "libavformat/avio.h"#include "libavdevice/avdevice.h"#include "libavcodec/avcodec.h"#include "libswscale/swscale.h"#include "libswresample/swresample.h"#include "libavutil/imgutils.h"}int flush_encoder(AVFormatContext *fmt_ctx, unsigned int stream_index){int ret;int got_frame;AVPacket enc_pkt;if (!(fmt_ctx->streams[stream_index]->codec->codec->capabilities &AV_CODEC_CAP_DELAY))return 0;while (1){enc_pkt.data = NULL;enc_pkt.size = 0;av_init_packet(&enc_pkt);ret = avcodec_encode_audio2(fmt_ctx->streams[stream_index]->codec, &enc_pkt,NULL, &got_frame);av_frame_free(NULL);if (ret < 0)break;if (!got_frame){ret = 0;break;}printf("Flush Encoder: Succeed to encode 1 frame!\tsize:%5d\n", enc_pkt.size);/* mux encoded frame */ret = av_write_frame(fmt_ctx, &enc_pkt);if (ret < 0)break;}return ret;}int main(int argc, char *argv[]){AVFormatContext *pFormatCtx = NULL;AVCodecContext *pCodecCtx = NULL;AVCodec *pCodec = NULL;AVFrame *pFrame = NULL;AVPacket pkt;int i = 0;const char *inFilename = "s16le.pcm";const char *outFilename = "output.mp3";avdevice_register_all();avformat_alloc_output_context2(&pFormatCtx, NULL, NULL, outFilename);if (avio_open(&pFormatCtx->pb, outFilename, AVIO_FLAG_READ_WRITE) < 0){printf("can't open output file\n");return -1;}AVStream *stream = avformat_new_stream(pFormatCtx, NULL);if (!stream){printf("can't allocate new stream\n");return -1;}//设置参数pCodecCtx = stream->codec;pCodecCtx->codec_id = pFormatCtx->oformat->audio_codec;pCodecCtx->codec_type = AVMEDIA_TYPE_AUDIO;pCodecCtx->sample_fmt = AV_SAMPLE_FMT_FLTP;pCodecCtx->sample_rate = 44100;pCodecCtx->channel_layout = AV_CH_LAYOUT_STEREO;pCodecCtx->channels = av_get_channel_layout_nb_channels(pCodecCtx->channel_layout);pCodecCtx->bit_rate = 128000;//pCodecCtx->frame_size = 1024;//查找编码器pCodec = avcodec_find_encoder(pCodecCtx->codec_id);//pCodec = avcodec_find_encoder_by_name("libfdk_aac");if (!pCodec){printf("can't find encoder\n");return -1;}//打开编码器if (avcodec_open2(pCodecCtx, pCodec, NULL) < 0){printf("can't open encoder\n");return -1;}pFrame = av_frame_alloc();if (!pFrame){printf("can't alloc frame\n");return -1;}pFrame->nb_samples = pCodecCtx->frame_size;pFrame->format = pCodecCtx->sample_fmt;pFrame->channels = 2;//PCM重采样SwrContext *swrCtx = swr_alloc();swr_alloc_set_opts(swrCtx, av_get_default_channel_layout(pCodecCtx->channels), pCodecCtx->sample_fmt,pCodecCtx->sample_rate, av_get_default_channel_layout(pFrame->channels), AV_SAMPLE_FMT_S16, //PCM源文件的采样格式44100, 0, NULL);swr_init(swrCtx);/* 分配空间 */uint8_t **convert_data = (uint8_t**) calloc(pCodecCtx->channels, sizeof(*convert_data));av_samples_alloc(convert_data, NULL, pCodecCtx->channels, pCodecCtx->frame_size, pCodecCtx->sample_fmt, 0);int size = av_samples_get_buffer_size(NULL, pCodecCtx->channels, pCodecCtx->frame_size, pCodecCtx->sample_fmt, 1);uint8_t *frameBuf = (uint8_t*) av_malloc(size);avcodec_fill_audio_frame(pFrame, pCodecCtx->channels, pCodecCtx->sample_fmt, (const uint8_t*) frameBuf, size, 1);//写帧头avformat_write_header(pFormatCtx, NULL);FILE *inFile = fopen(inFilename, "rb");av_init_packet(&pkt);pkt.data = NULL;pkt.size = 0;for (i = 0;; i++){//输入一帧数据的长度int length = pFrame->nb_samples * av_get_bytes_per_sample(AV_SAMPLE_FMT_S16) * pFrame->channels;printf("length = %d\n", length);//读PCM：特意注意读取的长度，否则可能出现转码之后声音变快或者变慢if (fread(frameBuf, 1, length, inFile) <= 0){printf("failed to read raw data\n");return -1;}else if (feof(inFile)){break;}swr_convert(swrCtx, convert_data, pCodecCtx->frame_size, (const uint8_t**) pFrame->data, pFrame->nb_samples);//输出一帧数据的长度length = pCodecCtx->frame_size * av_get_bytes_per_sample(pCodecCtx->sample_fmt);//双通道赋值（输出的AAC为双通道）memcpy(pFrame->data[0], convert_data[0], length);memcpy(pFrame->data[1], convert_data[1], length);pFrame->pts = i * 100;if (avcodec_send_frame(pCodecCtx, pFrame) < 0){printf("can't send frame for encoding\n");break;}if (avcodec_receive_packet(pCodecCtx, &pkt) >= 0){pkt.stream_index = stream->index;printf("write %4d frame, size = %d, length = %d\n", i, size, length);av_write_frame(pFormatCtx, &pkt);}av_packet_unref(&pkt);}//flush encoderif (flush_encoder(pFormatCtx, 0) < 0){printf("flushing encoder failed\n");return -1;}//write trailerav_write_trailer(pFormatCtx);avcodec_close(stream->codec);av_free(pFrame);av_free(frameBuf);avio_close(pFormatCtx->pb);avformat_free_context(pFormatCtx);fclose(inFile);return 0;}

看到几篇不错的博文

音频重采样

音频编码为AAC/MP3

常见音频编码格式