1.音频编码流程

在这里插入图片描述

2.编码函数API含义解释

av_frame_make_writable 确保帧数据可写，尽可能避免数据复制.如果帧可写，则不执行任何操作，如果不可写，则分配新缓冲区并复制数据.返回: 成功时为 0，错误时为负 AVERROR.

av_samples_fill_arrays 这个函数就是将你输入的一帧数据写入AVFrame格式输出,便于后面编码send,recvice使用

3.音频编码实战Demo PCM转AAC格式

编码注意点:

编码器相关配置得设置正确,比如码率,采样率,声道,采样格式等
也要设置AVFrame的格式,主要是采样率,声道,采样格式
如果数据不是FLTP格式的花,需要转化为FLTP格式.
PCM编码后的数据想要编码为AAC格式,得在前面加上adtsheader.

#ifndef MAINBACK_C
#define MAINBACK_C
#endif // MAINBACK_C
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <libavcodec/avcodec.h>
#include <libavutil/channel_layout.h>
#include <libavutil/common.h>
#include <libavutil/frame.h>
#include <libavutil/samplefmt.h>
#include <libavutil/opt.h>
void f32le_convert_to_fltp(float *f32le, float *fltp, int nb_samples) {float *fltp_l = fltp;   // 左通道float *fltp_r = fltp + nb_samples;   // 右通道for(int i = 0; i < nb_samples; i++) {fltp_l[i] = f32le[i*2];     // 0 1   - 2 3fltp_r[i] = f32le[i*2+1];   // 可以尝试注释左声道或者右声道听听声音}
}
static void get_adts_header(AVCodecContext *ctx, uint8_t *adts_header, int aac_length)
{uint8_t freq_idx = 0;    //0: 96000 Hz  3: 48000 Hz 4: 44100 Hzswitch (ctx->sample_rate) {case 96000: freq_idx = 0; break;case 88200: freq_idx = 1; break;case 64000: freq_idx = 2; break;case 48000: freq_idx = 3; break;case 44100: freq_idx = 4; break;case 32000: freq_idx = 5; break;case 24000: freq_idx = 6; break;case 22050: freq_idx = 7; break;case 16000: freq_idx = 8; break;case 12000: freq_idx = 9; break;case 11025: freq_idx = 10; break;case 8000: freq_idx = 11; break;case 7350: freq_idx = 12; break;default: freq_idx = 4; break;}uint8_t chanCfg = ctx->channels;uint32_t frame_length = aac_length + 7;adts_header[0] = 0xFF;adts_header[1] = 0xF1;adts_header[2] = ((ctx->profile) << 6) + (freq_idx << 2) + (chanCfg >> 2);adts_header[3] = (((chanCfg & 3) << 6) + (frame_length  >> 11));adts_header[4] = ((frame_length & 0x7FF) >> 3);adts_header[5] = (((frame_length & 7) << 5) + 0x1F);adts_header[6] = 0xFC;
}
int encode(AVCodecContext* codec_ctx,AVFrame* frame,AVPacket* pkt,FILE* out)
{int ret=0;ret = avcodec_send_frame(codec_ctx,frame);if(ret<0){printf("avcodec_send_frame failed\n");return ret;}while(1){ret=avcodec_receive_packet(codec_ctx,pkt);if(ret==AVERROR(EAGAIN)||ret==AVERROR(AVERROR_EOF))break;if(ret<0)return ret;if(codec_ctx->flags&AV_CODEC_FLAG_GLOBAL_HEADER){char header[7]={0};get_adts_header(codec_ctx,header,pkt->size);int size=fwrite(header,1,7,out);if(size!=7){printf("fwrite error\n");return 0;}}fwrite(pkt->data,1,pkt->size,out);}}
//编码流程  先初始化编码器，读取原始文件，send，recvice，写入
int main(int argc,char* argv[])
{if(argv<3){printf("argv<3\n");return -1;}char* pcm_path=argv[1];char* out_path=argv[2];FILE* pcm_file=fopen(pcm_path,"rb");FILE* out_file=fopen(out_path,"wb");AVCodec* codec=avcodec_find_encoder(AV_CODEC_ID_AAC);AVCodecContext* codec_ctx=avcodec_alloc_context3(codec);codec_ctx->bit_rate=100000;codec_ctx->channel_layout=AV_CH_LAYOUT_STEREO;codec_ctx->channels=av_get_channel_layout_nb_channels(codec_ctx->channel_layout);codec_ctx->sample_fmt=AV_SAMPLE_FMT_FLTP;
//    codec_ctx->codec_id=AV_CODEC_ID_AAC;
//    codec_ctx->codec_type=AVMEDIA_TYPE_AUDIO;codec_ctx->sample_rate=48000;codec_ctx->profile=FF_PROFILE_AAC_LOW;codec_ctx->flags|=AV_CODEC_FLAG_GLOBAL_HEADER;avcodec_open2(codec_ctx,codec,NULL);AVFrame* frame=av_frame_alloc();AVPacket* pkt=av_packet_alloc();
//    frame->channel_layout=codec_ctx->channel_layout;frame->channels=codec_ctx->channels;
//    frame->sample_rate=codec_ctx->sample_rate;frame->format=codec_ctx->sample_fmt;frame->nb_samples=codec_ctx->frame_size;av_frame_get_buffer(frame,0);//分配frame的buffint frame_bytes=av_get_bytes_per_sample(frame->format)*frame->channels*frame->nb_samples;uint8_t* pcm_buff=av_malloc(frame_bytes);memset(pcm_buff,0,frame_bytes);uint8_t *pcm_temp_buf = (uint8_t *)malloc(frame_bytes);memset(pcm_temp_buf,0,frame_bytes);int pts=0;int ret=0;while(1){int rsize=fread(pcm_buff,1,frame_bytes,pcm_file);ret = av_frame_make_writable(frame);if(ret != 0)printf("av_frame_make_writable failed, ret = %d\n", ret);f32le_convert_to_fltp(pcm_buff,pcm_temp_buf,frame->nb_samples);int need_size=av_samples_fill_arrays(frame->data,frame->linesize,pcm_temp_buf,frame->channels,frame->nb_samples,frame->format,0);if(rsize!=need_size)break;frame->pts=pts;pts+=1;printf("frame pts:%d\n",pts);encode(codec_ctx,frame,pkt,out_file);}encode(codec_ctx,NULL,pkt,out_file);return 0;
}