FFMEPGPCM编码为AAC

流程

下面附一张使用FFmpeg编码音频的流程图。使用该流程&＃xff0c;不仅可以编码AAC的音频&＃xff0c;而且可以编码MP3&＃xff0c;MP2等等各种FFmpeg支持的音频。图中蓝色背景的函数是实际输出数据的函数。浅绿色的函数是音频编码的函数。

简单介绍一下流程中各个函数的意义&＃xff1a;

av_register_all()&＃xff1a;注册FFmpeg所有编解码器。avformat_alloc_output_context2()&＃xff1a;初始化输出码流的AVFormatContext。avio_open()&＃xff1a;打开输出文件。av_new_stream()&＃xff1a;创建输出码流的AVStream。avcodec_find_encoder()&＃xff1a;查找编码器。avcodec_open2()&＃xff1a;打开编码器。avformat_write_header()&＃xff1a;写文件头&＃xff08;对于某些没有文件头的封装格式&＃xff0c;不需要此函数。比如说MPEG2TS&＃xff09;。avcodec_encode_audio2()&＃xff1a;编码音频。即将AVFrame&＃xff08;存储PCM采样数据&＃xff09;编码为AVPacket&＃xff08;存储AAC&＃xff0c;MP3等格式的码流数据&＃xff09;。av_write_frame()&＃xff1a;将编码后的视频码流写入文件。av_write_trailer()&＃xff1a;写文件尾&＃xff08;对于某些没有文件头的封装格式&＃xff0c;不需要此函数。比如说MPEG2TS&＃xff09;。


代码

/***最简单的基于FFmpeg的音频编码器*Simplest FFmpeg Audio Encoder**雷霄骅 Lei Xiaohua*leixiaohua1020&＃64;126.com*中国传媒大学/数字电视技术*Communication University of China / Digital TV Technology*http://blog.csdn.net/leixiaohua1020**本程序实现了音频PCM采样数据编码为压缩码流&＃xff08;MP3&＃xff0c;WMA&＃xff0c;AAC等&＃xff09;。*是最简单的FFmpeg音频编码方面的教程。*通过学习本例子可以了解FFmpeg的编码流程。*This software encode PCM data to AAC bitstream.*It&＃39;s the simplest audio encoding software based on FFmpeg.*Suitable for beginner of FFmpeg*/#include // 包含ffmpeg头文件
#include "libavutil/avutil.h"#include "libavcodec/avcodec.h"#include "libavformat/avformat.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 &＃61; NULL;enc_pkt.size &＃61; 0;av_init_packet(&enc_pkt);ret &＃61; 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&＃61;0;break;}printf("Flush Encoder: Succeed to encode 1 frame!\tsize:%5d\n",enc_pkt.size);/* mux encoded frame */ret &＃61; av_write_frame(fmt_ctx, &enc_pkt);if (ret < 0)break;}return ret;
}int main(int argc, char* argv[])
{AVFormatContext* pFormatCtx;AVOutputFormat* fmt;AVStream* audio_st;AVCodecContext* pCodecCtx;AVCodec* pCodec;uint8_t* frame_buf;AVFrame* pFrame;AVPacket pkt;int got_frame&＃61;0;int ret&＃61;0;int size&＃61;0;FILE *in_file&＃61;NULL; //Raw PCM dataint framenum&＃61;1000; //Audio frame numberconst char* out_file &＃61; "tdjm.aac"; //Output URLint i;in_file&＃61; fopen("2000-01-01_015202.pcm", "rb");av_register_all();//Method 1.pFormatCtx &＃61; avformat_alloc_context();fmt &＃61; av_guess_format(NULL, out_file, NULL);pFormatCtx->oformat &＃61; fmt;//Method 2.//avformat_alloc_output_context2(&pFormatCtx, NULL, NULL, out_file);//fmt &＃61; pFormatCtx->oformat;//Open output URLif (avio_open(&pFormatCtx->pb,out_file, AVIO_FLAG_READ_WRITE) < 0){printf("Failed to open output file!\n");return -1;}audio_st &＃61; avformat_new_stream(pFormatCtx, 0);if (audio_st&＃61;&＃61;NULL){return -1;}//根据需要转化的pcm数据进行设置pCodecCtx &＃61; audio_st->codec;pCodecCtx->codec_id &＃61; fmt->audio_codec;pCodecCtx->codec_type &＃61; AVMEDIA_TYPE_AUDIO;pCodecCtx->sample_fmt &＃61; AV_SAMPLE_FMT_FLT;pCodecCtx->sample_rate&＃61; 16000;pCodecCtx->channel_layout&＃61;AV_CH_LAYOUT_MONO;pCodecCtx->channels &＃61; av_get_channel_layout_nb_channels(pCodecCtx->channel_layout);pCodecCtx->bit_rate &＃61; 32000;//Show some informationav_dump_format(pFormatCtx, 0, out_file, 1);pCodec &＃61; avcodec_find_encoder(pCodecCtx->codec_id);if (!pCodec){printf("Can not find encoder!\n");return -1;}if (avcodec_open2(pCodecCtx, pCodec,NULL) < 0){printf("Failed to open encoder!\n");return -1;}pFrame &＃61; av_frame_alloc();pFrame->nb_samples&＃61; pCodecCtx->frame_size;pFrame->format&＃61; pCodecCtx->sample_fmt;size &＃61; av_samples_get_buffer_size(NULL, pCodecCtx->channels,pCodecCtx->frame_size,pCodecCtx->sample_fmt, 1);frame_buf &＃61; (uint8_t *)av_malloc(size);avcodec_fill_audio_frame(pFrame, pCodecCtx->channels, pCodecCtx->sample_fmt,(const uint8_t*)frame_buf, size, 1);//Write Headeravformat_write_header(pFormatCtx,NULL);av_new_packet(&pkt,size);for (i&＃61;0; i<framenum; i&＃43;&＃43;){//Read PCMif (fread(frame_buf, 1, size, in_file) <&＃61; 0){printf("Failed to read raw data! \n");return -1;}else if(feof(in_file)){break;}pFrame->data[0] &＃61; frame_buf; //PCM DatapFrame->pts&＃61;i*100;got_frame&＃61;0;//Encoderet &＃61; avcodec_encode_audio2(pCodecCtx, &pkt,pFrame, &got_frame);if(ret < 0){printf("Failed to encode!\n");//return -1;}if (got_frame&＃61;&＃61;1){printf("Succeed to encode 1 frame! \tsize:%5d\n",pkt.size);pkt.stream_index &＃61; audio_st->index;ret &＃61; av_write_frame(pFormatCtx, &pkt);av_free_packet(&pkt);}}//Flush Encoderret &＃61; flush_encoder(pFormatCtx,0);if (ret < 0) {printf("Flushing encoder failed\n");return -1;}//Write Trailerav_write_trailer(pFormatCtx);//Cleanif (audio_st){avcodec_close(audio_st->codec);av_free(pFrame);av_free(frame_buf);}avio_close(pFormatCtx->pb);avformat_free_context(pFormatCtx);fclose(in_file);return 0;
}


参考文献

1、https://blog.csdn.net/leixiaohua1020/article/details/25430449