ffmpeg 解码音频（aac、mp3）输出pcm文件
播放pcm可以参考： ffplay -ar 48000 -ac 2 -f f32le out.pcm
main.c
#include <stdio.h>#include <stdlib.h>#include <string.h>#include <libavutil/frame.h>#include <libavutil/mem.h>#include <libavcodec/avcodec.h>#define AUDIO_INBUF_SIZE 10240#define AUDIO_REFILL_THRESH 4096static void decode(AVCodecContext* dec_ctx, AVPacket* pkt, AVFrame* frame, FILE *outfile){int i, ch;int ret, sample_size;int send_ret = 1;do{//传入要解码的packetret = avcodec_send_packet(dec_ctx, pkt);//AVERROR(EAGAIN) 传入失败，表示先要receive frame再重新send packetif(ret == AVERROR(EAGAIN)){send_ret = 0;fprintf(stderr, "avcodec_send_packet = AVERROR(EAGAIN)\n");}else if(ret < 0){char err[128] = {0};av_strerror(ret, err, 128);fprintf(stderr, "avcodec_send_packet = ret < 0 : %s\n", err);return;}while (ret >= 0){//调用avcodec_receive_frame会在内部首先调用av_frame_unref来释放frame本来的数据//就是这次调用会将上次调用返回的frame数据释放ret = avcodec_receive_frame(dec_ctx, frame);if(ret == AVERROR(EAGAIN) || ret == AVERROR_EOF)return;else if(ret < 0){fprintf(stderr, "avcodec_receive_frame = ret < 0\n");exit(1);}//获取采样点占用的字节sample_size = av_get_bytes_per_sample(dec_ctx->sample_fmt);if(sample_size < 0){fprintf(stderr, "av_get_bytes_per_sample = sample_size < 0\n");exit(1);}//在第一帧的时候输出一下音频信息static int print_info = 1;if(print_info){print_info = 0;printf("ar-samplerate: %uHz\n", frame->sample_rate);printf("ac-channel: %u\n", frame->channels);printf("f-format: %u\n", frame->format);}//平面方式：//LLLLRRRRLLLLRRRRLLLLRRRR(LLLLRRRR这样为一个音频帧)//交错方式：//LRLRLRLRLRLRLRLRLR (LR这样为一个音频样本)//按交错方式写入(nb_samples这一帧多少样本)for(i = 0; i < frame->nb_samples; i++){//dec_ctx->channels 多少个通道的数据for(int channle = 0; channle < dec_ctx->channels; channle++){//frame->data[0] = L 通道//frame->data[1] = R 通道fwrite(frame->data[channle] + sample_size * i, 1, sample_size, outfile);}}}}while(!send_ret);}#define AAC 0int main(){const char* outfilename = "out.pcm";#if AACconst char* filename = "test.aac";#elseconst char* filename = "test.mp3";#endifconst AVCodec *codec;AVCodecContext *codec_ctx= NULL;AVCodecParserContext *parser = NULL;int len = 0;int ret = 0;FILE *infile = NULL;FILE *outfile = NULL;uint8_t inbuf[AUDIO_INBUF_SIZE + AV_INPUT_BUFFER_PADDING_SIZE];uint8_t *data = NULL;size_t data_size = 0;AVPacket *pkt = NULL;AVFrame *de_frame = NULL;//申请AVPacket本身的内存pkt = av_packet_alloc();//要使用的解码器IDenum AVCodecID audio_codec_id = AV_CODEC_ID_AAC;if(strstr(filename, "aac") != NULL){audio_codec_id = AV_CODEC_ID_AAC;}else if(strstr(filename, ".mp3") != NULL){audio_codec_id = AV_CODEC_ID_MP3;}else{printf("audio_codec_id = AV_CODEC_ID_NONE\n");return 0;}//查找相应的解码器codec = avcodec_find_decoder(audio_codec_id);if(!codec){printf("Codec not find!\n");return 0;}//根据解码器ID获取裸流的解析器parser = av_parser_init(codec->id);if(!parser){printf("Parser not find!\n");return 0;}//分配codec使用的上下文codec_ctx = avcodec_alloc_context3(codec);if(!codec_ctx){printf("avcodec_alloc_context3 failed!\n");return 0;}//将解码器和解码使用的上下文关联if(avcodec_open2(codec_ctx, codec, NULL) < 0){printf("avcodec_open2 failed!\n");return 0;}//打开输入文件infile = fopen(filename, "rb");if(!infile){printf("infile fopen failed!\n");return 0;}//输出文件outfile = fopen(outfilename, "wb");if(!outfile){printf("outfilie fopen failed!\n");return 0;}int file_end = 0;//读取文件开始解码data = inbuf;data_size = fread(inbuf, 1, AUDIO_INBUF_SIZE, infile);de_frame = av_frame_alloc();while (data_size > 0){//获取传入到avcodec_send_packet一个packet的数据量//（一帧的量可能也会多帧的量，这里测试是一帧的量）ret = av_parser_parse2(parser, codec_ctx, &pkt->data, &pkt->size,data, data_size,AV_NOPTS_VALUE, AV_NOPTS_VALUE, 0);if(ret < 0){printf("av_parser_parser2 Error!\n");return 0;}//使用了多少数据做一个偏移data += ret;data_size -= ret;if(pkt->size)decode(codec_ctx, pkt, de_frame, outfile);//如果当前缓冲区中数据少于AUDIO_REFILL_THRESH就再读//避免多次读文件if((data_size < AUDIO_REFILL_THRESH) && !file_end ){//剩余数据移动缓冲区前memmove(inbuf, data, data_size);data = inbuf;//跨过已有数据存储len = fread(data + data_size, 1, AUDIO_INBUF_SIZE - data_size, infile);if(len > 0)data_size += len;else if(len == 0){file_end = 1;printf("file end!\n");}}}//冲刷解码器pkt->data = NULL;pkt->size = 0;decode(codec_ctx, pkt, de_frame, outfile);fclose(infile);fclose(outfile);avcodec_free_context(&codec_ctx);av_parser_close(parser);av_frame_free(&de_frame);av_packet_free(&pkt);printf("audio decoder end!\n");return 0;}
