音視頻開發(fā)進(jìn)階指南(第二章)

書中示例源碼地址：
ffmpeg編譯參考鏈接
使用libmp3lame開源庫范抓，編碼PCM數(shù)據(jù)為MP3蚊伞，結(jié)尾有源碼叫编，分支為chapter_2.x

一杯活、新建NDK工程

網(wǎng)上一大堆。

二蜂绎、下載LAME源碼

lame源碼地址lame官網(wǎng)
下載后解壓栅表，本demo中中使用的是3.100版本

三、拷貝libmp3lame源碼到工程

在項(xiàng)目cpp目錄下新建libmp3lame目錄师枣，用來存放下載的源碼怪瓶。
找到解壓 的libmp3lame文件夾，將里面的.c和.h文件全部復(fù)制到項(xiàng)目的cpp/libmp3lame目錄中践美。 libmp3lame文件夾內(nèi)還包含其他文件夾洗贰，例如vector和i386是不需要的，可以忽略陨倡，然后敛滋，再找到解壓的include文件夾，將lame.h文件拷貝到cpp/libmp3lame目錄中兴革，一共拷貝43個(gè)文件绎晃。

移植過來的代碼要做一些修改才能編譯通過：

1）刪除fft.c文件的47行的”include “vector/lame_intrin.h”“
2）修改set_get.h文件的24行的#include“l(fā)ame.h”
3）將util.h文件的574行的”extern ieee754_float32_tfast_log2(ieee754_float32_t x);”  替換為 “extern float fast_log2(float x);”

四、編寫編碼工具類

mp3_encoder.h

#include <stdio.h>
#include "jni.h"
#include "../libmp3lame/lame.h"

class Mp3Encoder {
private:
    FILE *pcmFile;
    FILE *mp3File;
    lame_t lameClient;
public:
    Mp3Encoder();

    ~Mp3Encoder();

    int Init(const char *pcmFilePath, const char *mp3FilePath,
             int sampleRate, int channels, int bitRate);

    void Encode();

    void Destory();
};

mp3_encoder.cpp

//
// Created by bian on 2019/10/10.
//
#include "stdio.h"
#include <android/log.h>
#include <mp3_encoder.h>

#define LOG_TAG "Mp3Encorder"
#define LOGI(FORMAT, ...) __android_log_print(ANDROID_LOG_INFO,LOG_TAG,FORMAT,##__VA_ARGS__);
#define LOGE(FORMAT, ...) __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,FORMAT,##__VA_ARGS__);


int Mp3Encoder::Init(const char *pcmFilePath, const char *mp3FilePath,
                     int sampleRate, int channels, int bitRate) {
    int ret = -1;
    pcmFile = fopen(pcmFilePath, "rb");//rb-以二進(jìn)制讀取模式打開文件
    if (pcmFile) {
        mp3File = fopen(mp3FilePath, "wb");//wb-以二進(jìn)制寫入模式打開文件
        if (mp3File) {
            lameClient = lame_init();
            lame_set_in_samplerate(lameClient, sampleRate);//輸入采樣率
            lame_set_out_samplerate(lameClient, sampleRate);//輸出采樣率
            lame_set_num_channels(lameClient, channels);//聲道個(gè)數(shù)
            lame_set_brate(lameClient, bitRate / 1000);//比特率
            lame_init_params(lameClient);
            ret = 0;
            LOGI("set lameClient params done!")
        } else {
            LOGE("open mp3File failed! path=%s", mp3FilePath);
        }

    } else {
        LOGE("open pcmFile failed! path=%s", pcmFilePath);
    }
    return ret;
}

void Mp3Encoder::Encode() {
    int channels = lame_get_num_channels(lameClient);
    LOGI("通道個(gè)數(shù)為：%d", channels);

    int bufferSize = 1024 * 256;//緩沖區(qū)大小
    short *buffer = new short[bufferSize / channels];//讀取pcmFile的緩沖區(qū)

    //雙聲道情況時(shí)杂曲，為左右聲道分配緩沖區(qū)
    short *leftBuffer = new short[bufferSize / 4]; //左聲道緩沖區(qū)
    short *rightBuffer = new short[bufferSize / 4];//右聲道緩沖區(qū)

    unsigned char *mp3_buffer = new unsigned char[bufferSize];

    size_t readBufferSize = 0;
    int frameSize = sizeof(short int) * channels;//一個(gè)幀的字節(jié)數(shù)
    LOGI("frameSize=%d", frameSize);
    while ((readBufferSize = fread(buffer, frameSize, bufferSize / channels,
                                   pcmFile)) > 0) {
        if (channels == 1) {
            LOGI("readBufferSize=%d", readBufferSize);
            //對(duì)pcm數(shù)據(jù)進(jìn)行編碼庶艾，單聲道情況，右聲道為空
            size_t wroteSize = lame_encode_buffer(lameClient,
                                                  (short int *) buffer,//左聲道
                                                  NULL,//右聲道
                                                  (int) (readBufferSize),
                                                  mp3_buffer,//編譯后的數(shù)據(jù)
                                                  bufferSize);
            LOGI("wroteSize=%d", wroteSize);
            fwrite(mp3_buffer, 1, wroteSize, mp3File);//寫入編碼后的數(shù)據(jù)到mp3File
        } else if (channels == 2) {
            for (int i = 0; i < readBufferSize; i++) {
                if (i % 2 == 0) {
                    leftBuffer[i / 2] = buffer[i];
                } else {
                    rightBuffer[i / 2] = buffer[i];
                }
            }
            //對(duì)pcm數(shù)據(jù)進(jìn)行編碼
            size_t wroteSize = lame_encode_buffer(lameClient,
                                                  (short int *) leftBuffer,//左聲道
                                                  (short int *) rightBuffer,//右聲道
                                                  (int) (readBufferSize / 2),
                                                  mp3_buffer,//編譯后的數(shù)據(jù)
                                                  bufferSize);
            fwrite(mp3_buffer, 1, wroteSize, mp3File);//寫入編碼后的數(shù)據(jù)到mp3File
        }
    }
    delete[] buffer;
    delete[] leftBuffer;
    delete[] rightBuffer;
    delete[] mp3_buffer;

}

void Mp3Encoder::Destory() {
    if (pcmFile) {
        fclose(pcmFile);
    }
    if (mp3File) {
        fclose(mp3File);
        lame_close(lameClient);
    }
}

Mp3Encoder::Mp3Encoder() {
}

Mp3Encoder::~Mp3Encoder() {
}

五擎勘、在java中調(diào)用

新建類Mp3Encoder.java

public class Mp3Encoder {
    public native int init(String pcmPath, int audioChannels,
                           int bitRate, int sampleRate, String mp3Path);

    public native void encode();
    public native void destroy();
}

生成頭文件
在Mp3Encoder右鍵落竹，如下圖

image.png

如果你沒有，請(qǐng)點(diǎn)擊File->Settings->Tools->External Tools,點(diǎn)擊+號(hào)货抄，按照下圖照抄即可

image.png

最后是JNI開發(fā)
Mp3Encoder.cpp

Mp3Encoder *encoder;

JNIEXPORT jint JNICALL Java_com_flyscale_mp3encoder_Mp3Encoder_init
        (JNIEnv *env, jobject jclazz, jstring pcmFileParam, jint channels,
         jint bitRate, jint sampleRate, jstring mp3FileParam) {
    int ret = -1;
    const char *pcmPath = env->GetStringUTFChars(pcmFileParam, NULL);
    const char *mp3Path = env->GetStringUTFChars(mp3FileParam, NULL);
    encoder = new Mp3Encoder();
    ret = encoder->Init(pcmPath, mp3Path, sampleRate, channels, bitRate);
    env->ReleaseStringUTFChars(mp3FileParam, mp3Path);
    env->ReleaseStringUTFChars(pcmFileParam, pcmPath);
    return ret;
}

JNIEXPORT void JNICALL Java_com_flyscale_mp3encoder_Mp3Encoder_encode(JNIEnv *env, jobject jclazz) {
    LOGI("encoder encode");
    encoder->Encode();
}

JNIEXPORT void JNICALL Java_com_flyscale_mp3encoder_Mp3Encoder_destroy
        (JNIEnv *env, jobject jclazz) {
    encoder->Destory();
}

六述召、編寫CMakeLists.txt

依賴lame庫的方式有幾種，我直接把lame的源碼與我自己的源碼放在一起進(jìn)行編譯蟹地。

#指定使用的cmake最低版本號(hào)
cmake_minimum_required(VERSION 3.4.1)

#指定工程名积暖，非必須
project(mp3encoder)

#指定頭文件路徑
include_directories(src/main/cpp/include/)

set(SRC_FILES
        src/main/cpp/Mp3Encoder.cpp
        src/main/cpp/mp3_encoder.cpp
        src/main/cpp/libmp3lame/bitstream.c
        src/main/cpp/libmp3lame/encoder.c
        src/main/cpp/libmp3lame/fft.c
        src/main/cpp/libmp3lame/gain_analysis.c
        src/main/cpp/libmp3lame/id3tag.c
        src/main/cpp/libmp3lame/lame.c
        src/main/cpp/libmp3lame/mpglib_interface.c
        src/main/cpp/libmp3lame/newmdct.c
        src/main/cpp/libmp3lame/presets.c
        src/main/cpp/libmp3lame/psymodel.c
        src/main/cpp/libmp3lame/quantize_pvt.c
        src/main/cpp/libmp3lame/quantize.c
        src/main/cpp/libmp3lame/reservoir.c
        src/main/cpp/libmp3lame/set_get.c
        src/main/cpp/libmp3lame/tables.c
        src/main/cpp/libmp3lame/takehiro.c
        src/main/cpp/libmp3lame/util.c
        src/main/cpp/libmp3lame/vbrquantize.c
        src/main/cpp/libmp3lame/VbrTag.c
        src/main/cpp/libmp3lame/version.c
        )
#編譯為共享庫，名稱audioencoder
add_library(
        audioencoder

        # Sets the library as a shared library.
        SHARED

        #源文件路徑
        ${SRC_FILES})



#在默認(rèn)路徑下查找log庫怪与，并保存在變量log-lib中
find_library(log-lib log)

# 鏈接庫
target_link_libraries( # Specifies the target library.
        audioencoder

        # 將Log-lib變量代表的庫夺刑，鏈接到audioencoder庫
        ${log-lib})

七、PCM源與參數(shù)問題

pcm音頻源文件分單通道和雙通道分别，采樣率遍愿，比特率，所以要轉(zhuǎn)碼時(shí)要注意根據(jù)PCM源文件的情況進(jìn)行區(qū)分耘斩，是進(jìn)行單通道編碼還是雙通道編碼沼填。例子中也有體現(xiàn)。否則可以會(huì)出現(xiàn)聲音變慢括授，變快坞笙，有雜音岩饼，有空白等情況。

github源碼
[PCM音頻數(shù)據(jù)](https://pan.baidu.com/s/136sjYRJlQY5uYy7F1hzPKg
提取碼：h7wv)

參考

使用libmp3lame庫編碼mp3
Android移植lame庫(采用CMake)