faac库编码PCM数据

简介

AAC（Advanced Audio Coding），一种音频编码技术。具体有哪些特点和优点，自行去百度或google吧。

函数简介

faac是一个成熟的AAC编码库。其提供的主要接口函数如下：

faacEncOpen

faacEncHandle FAACAPI faacEncOpen     (        unsigned long sampleRate,        unsigned int numChannels,        unsigned long *inputSamples,        unsigned long *maxOutputBytes           );

* sampleRate *：采样率
* numChannels *：声道数
* inputSamples * ：编码时每次需要输入的字节数
* maxOutputBytes * : 编码时输出的最大字节数

该函数主要是创建一个编码器，并且返回需要输入的字节及编码返回的最大字节数

faacEncClose

void FAACAPI faacEncClose( faccEncHandle hEncoder);

与上述接口相对应，关闭编码器。

faacEncGetCurrentConfiguration

faacEncConfigurationPtr FAACAPI faacEncGetCurrentConfiguration( faccEncHandle hEncoder);

该函数获取当前编码器的配置

faacEncGetCurrentConfiguration

faacEncConfigurationPtr FAACAPI faacEncSetCurrentConfiguration(     faccEncHandle hEncoder,    faacEncConfigurationPtr config);

该函数设置当前编码器的配置
​

faacEncEncode

int FAACAPI faacEncEncode(    faacEncHandle hEncoder,   int32_t *inputBuffer,    unsigned int samplesInput,    unsigned char *outputBuffer,    unsigned int bufferSize);

* hEncoder *：编码器，通过faacEncOpen函数创建的
* inputBuffer *：输入数据
* sampleInput *：输入数据大小，如果为0，则编码器会把换成的数据都给输出
* outputBuffer *：存放输出数据
* bufferSize *：存放输出数据的缓存区大小，至少是和maxOutputBytes一样的大小

该函数进行编码

faacEncConfigurationPtr 结构

typedef struct faacEncConfiguration{    unsigned int mpegVersion;    unsigned int aacObjectType;    unsigned int allowMidside;    unsigned int useLfe;    unsigned int useTns;    unsigned long bitRate;    unsigned int bandWidth;    ...}faacEncConfiguration, *faacEncConfigurationPtr;

简单的介绍其中的几个参数

mpegVersion ：mpeg版本， MPEG2/MPEG4aacObjectType：MAIN/LOW/LTPallowMidside：mid/side codinguseLfe：低频增强useTns：瞬时噪声定形(temporal noise shaping，TNS)滤波器bitRate ：码率bandWidth：占用的带宽outputFormat：输出格式，0 = Raw, 1 = ADTSinputFormat：输入格式，FAAC_INPUT_NULL/FAAC_INPUT_16BIT/FAAC_INPUT_24BIT/FAAC_INPUT_32BIT/FAAC_INPUT_FLOAT

代码如下

/* aac_encode.c */#include <stdio.h>#include <faac.h>#include <stdint.h>#include <stdlib.h>#include <string.h>int main (int argc, char **argv){    unsigned long sampleRate = 8000;    unsigned int numChannels = 1;    unsigned long inputSample = 0;    unsigned long maxOutputBytes = 0;    faacEncHandle encoder;    faacEncConfigurationPtr config;    FILE *rfile = NULL;    FILE *wfile = NULL;    int16_t *pcm_input = NULL;    uint8_t *aac_output = NULL;    int readcount = 0;    int writecount = 0;    encoder = faacEncOpen(sampleRate, numChannels, &inputSample, &maxOutputBytes);    config = faacEncGetCurrentConfiguration(encoder);    config->aacObjectType = MAIN;    config->mpegVersion = MPEG4;    //config->useLfe = 1;    config->useTns = 1;    config->allowMidside = 1;    config->outputFormat = 1;  // RAW_STREAM = 0, ADTS_STREAM 1    //config->bitRate = ;    config->inputFormat = FAAC_INPUT_16BIT;    faacEncSetConfiguration(encoder, config);    printf("sampleRate:%ld, numChannels:%d, inputSample:%ld, maxOutputBytes:%ld\n",             sampleRate, numChannels, inputSample, maxOutputBytes);    if (argv[1]) {        rfile = fopen(argv[1], "rb");    } else {        printf("try to open /tmp/input.pcm\n");        rfile = fopen("/tmp/input.pcm", "rb");    }    if (!rfile) {        printf("open error\n");        goto end;    }    if (argv[2]) {        wfile = fopen(argv[2], "wb");    } else {        printf("try to open /tmp/output.aac\n");        wfile = fopen("/tmp/output.aac", "wb");    }    if (!wfile) {        printf("open error\n");        goto end;    }    pcm_input = (int16_t *)malloc(inputSample * sizeof(int16_t));    aac_output = (uint8_t *)malloc(maxOutputBytes * sizeof(uint8_t));    /* encode */    while (1) {        int readlen = 0;        int ret = 0;        readlen = fread(pcm_input, sizeof(int16_t), inputSample, rfile);        //printf("====================read %d\n", readlen);        ret = faacEncEncode(encoder, (int32_t *)pcm_input, readlen, aac_output, maxOutputBytes);        if (ret > 0) {            //printf("encode success! ret %d\n", ret);            fwrite(aac_output, sizeof(uint8_t), ret, wfile);        } else if (ret < 0) {            printf("encode error\n");            break;        }        readcount += readlen * 2;        writecount += ret;        if (!readlen && !ret) {            printf("encode complete, from %d bytes to %d bytes\n", readcount, writecount);            break;        }    }    free(pcm_input);    free(aac_output);  end:    if (wfile) fclose(wfile);    if (rfile) fclose(rfile);    faacEncClose(encoder);    return 0;}

/* Makefile */all: aacaac: aac_encode.c Makefile    gcc -O3 -Wall -Werror -Wno-unused aac_encode.c -lfaac -o aac_encclean:    rm -rf aac_enc

最后编译，运行即可

make./aac_enc /tmp/北京北京8k16bits单声道.pcm /tmp/output.aac

使用播放器打开output.aac即可

注意：以上代码在MacOS 10.10.4 上编译并运行通过