FFmpeg —— 15.示例程序（九）：音频编码器（PCM编码为MP3）

た入场券 2021-09-24 04:32 675阅读 0赞

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_MACROS
    
    
    extern "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 encoder
    	if (flush_encoder(pFormatCtx, 0) < 0)
    	{
    		printf("flushing encoder failed\n");
    		return -1;
    	}
    
    	//write trailer
    	av_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][Link 1]

[音频编码为AAC/MP3][AAC_MP3]

[常见音频编码格式 ][Link 2]

[Link 1]: https://www.jianshu.com/p/b0627f8ac018
[AAC_MP3]: https://www.jianshu.com/p/a1fb602b9d7f
[Link 2]: https://blog.csdn.net/houxiaoni01/article/details/78810674