ffmpeg编码之PCM到AAC

编码前文件

编码后文件

 编码过程

实现方式

extern "C"
{
	#include <libavformat\avformat.h>
	#include <libswscale\swscale.h>
	#include <libswresample\swresample.h>
}

#include <iostream>
using namespace std;
#pragma comment(lib,"avformat.lib")
#pragma comment(lib,"avcodec.lib")
#pragma comment(lib,"avutil.lib")
#pragma comment(lib,"swscale.lib")
#pragma comment(lib,"swresample.lib")

int main()
{
	char infile[] = "16.wav";
	char outfile[] = "out.aac";

	//register muxer,demuters 格式
	av_register_all();
	//register codec
	avcodec_register_all();

	//1  打开音频编码器
	AVCodec *codec = avcodec_find_encoder(AV_CODEC_ID_AAC);
	if (!codec)
	{
		cout << "avcodec_find_encoder error" << endl;
		getchar();
		return -1;
	}
	//编码器上下文
	AVCodecContext *c = avcodec_alloc_context3(codec);
	if (!c)
	{
		cout << "avcodec_alloc_context3 error" << endl;
		getchar();
		return -1;
	}
	//编码器参数设置
	c->bit_rate = 64000;//比特率  ：每秒传输的比特(bit)数,比特率越高，传输数据速度越快
	//采样率:每秒采集的样本数
	c->sample_rate = 44100;
	//样本格式和存储方式  float, planar
	c->sample_fmt = AV_SAMPLE_FMT_FLTP;
	//音频通道布局 先存放左声道，然后右声道
	c->channel_layout = AV_CH_LAYOUT_STEREO;
	//通道数
	c->channels = 2;
	c->flags |= AV_CODEC_FLAG_GLOBAL_HEADER;

	//打开编码器
	int ret = avcodec_open2(c,codec,NULL);
	if (ret < 0)
	{
		cout << "avcodec_open2 error" << endl;
		getchar();
		return -1;
	}
	cout << "avcodec_open2 success!" << endl;

	//2 打开输出封装的上下文
	AVFormatContext *oc = NULL;
	avformat_alloc_output_context2(&oc,NULL,NULL,outfile);
	if (!oc)
	{
		cout << "avformat_alloc_output_context2 error" << endl;
		getchar();
		return -1;
	}

	//第二个参数为空，就是根据文件格式，自动选择合适的编码器
	AVStream *st = avformat_new_stream(oc,NULL);
	st->codecpar->codec_tag = 0;
	avcodec_parameters_from_context(st->codecpar,c);


	//3,open io,write head
	ret = avio_open(&oc->pb,outfile,AVIO_FLAG_WRITE);
	if (ret < 0)
	{
		cout << "avio_open error" << endl;
		getchar();
		return -1;
	}
	//写文件头
	ret = avformat_write_header(oc,NULL);

	//4 创建音频重采样上下文
	SwrContext *actx = NULL;
	actx = swr_alloc_set_opts(actx,
		c->channel_layout,c->sample_fmt,c->sample_rate,//输出格式
		AV_CH_LAYOUT_STEREO,AV_SAMPLE_FMT_S16,44100,//输入格式
	0,0);
	if (!actx)
	{
		cout << "swr_alloc_set_opts error" << endl;
		getchar();
		return -1;
	}
	ret = swr_init(actx);
	if (ret < 0)
	{
		cout << "swr_init error" << endl;
		getchar();
		return -1;
	}
	//5 打开输入音频文件，进行重采样
	AVFrame *frame = av_frame_alloc();
	frame->format = AV_SAMPLE_FMT_FLTP;
	frame->channels = 2;
	//音频通道布局
	frame->channel_layout = AV_CH_LAYOUT_STEREO;
	frame->nb_samples = 1024;//一帧音频存放的样本数量
	ret = av_frame_get_buffer(frame,0);
	if (ret < 0)
	{
		cout << "av_frame_get_buffer error" << endl;
		getchar();
		return -1;
	}

	int readSize = frame->nb_samples * 2 * 2;
	char *pcm = new char[readSize];
	FILE *fp = fopen(infile,"rb");

	//开始编码
	for (;;)
	{
		int len = fread(pcm,1,readSize,fp);
		if (len<=0)
		{
			break;
		}
		const uint8_t *data[1];
		data[0] = (uint8_t*)pcm;

		len = swr_convert(actx, frame->data, frame->nb_samples,
			data, frame->nb_samples
		);
		if (len <= 0) {
			break;
		}

		AVPacket pkt;
		av_init_packet(&pkt);

		//6 音频编码
		ret = avcodec_send_frame(c,frame);
		if (ret != 0) continue;
		ret = avcodec_receive_packet(c,&pkt);
		if (ret != 0) continue;

		//7 音频封装成aac文件
		pkt.stream_index = 0;
		pkt.pts = 0;
		pkt.dts = 0;
		ret = av_interleaved_write_frame(oc,&pkt);
		cout << "[" << len << "]";
	}

	delete pcm;
	pcm = NULL;

	//写文件尾
	av_write_trailer(oc);

	//关闭输出流
	avio_close(oc->pb);
	//清理封装输出上下文
	avformat_free_context(oc);

	//关闭编码器
	avcodec_close(c);
	//清理编码器上下文
	avcodec_free_context(&c);

	cout << "======================end=========================" << endl;
	getchar();
	return 0;
}