android平臺下音訊編碼之編譯LAME庫轉碼PCM為MP3
阿新 • • 發佈：2018-12-20
ffmpeg實踐學習
目錄
音訊概述
一般來說音訊的裸資料格式就是脈衝編碼調製(PCM)資料。描述一段PCM資料一般需要以下幾個概念：量化格式(sampleFormat)、取樣率(sampleRate)、聲道數(channel)。以CD的音質為例：量化格式為16位元(2位元組)，取樣率為44100，聲道數為2，這些資訊就描述了CD的音質。而對於聲音格式，還有一個概念用來描述它的大小，稱為資料位元率，即1秒時間內的位元數目，它用於衡量音訊資料單位時間內的容量大小。
上述的裸資料要在網路中實時線上傳播的話，那麼這個資料量比較大，所以必須對其進行壓縮編碼，常見的由WAV、AAC、MP3、Ogg等
開始配置交叉編譯指令碼
還是直接複用之前的環境配置指令碼config.sh
#NDK路徑
export ANDROID_NDK_ROOT=/home/byhook/android/android-ndk-r10e
export AOSP_TOOLCHAIN_SUFFIX=4.9
export AOSP_API="android-21"
#架構
if [ "$#" -lt 1 ]; then
THE_ARCH=armv7
else
THE_ARCH=$(tr [A-Z] [a-z] <<< "$1")
fi
#根據不同架構配置環境變數
case "$THE_ARCH" in
arm|armv5| 編寫交叉編譯指令碼：build_lame.sh
可以根據自己需要決定是否只需要動態庫或者靜態庫，筆者兩個都輸出來了。
#!/bin/bash
ARCH=$1
source config.sh $ARCH
LIBS_DIR=$(cd `dirname $0`; pwd)/libs/liblame
echo "LIBS_DIR="$LIBS_DIR
cd lame-3.100
PLATFORM=$ANDROID_NDK_ROOT/platforms/$AOSP_API/$AOSP_ARCH
TOOLCHAIN=$ANDROID_NDK_ROOT/toolchains/$TOOLCHAIN_BASE-$AOSP_TOOLCHAIN_SUFFIX/prebuilt/linux-x86_64
CROSS_COMPILE=$TOOLCHAIN/bin/$TOOLNAME_BASE-
SYSROOT=$ANDROID_NDK_ROOT/platforms/$AOSP_API/$AOSP_ARCH
PREFIX=$LIBS_DIR/$AOSP_ABI
CFLAGS=""
FLAGS="--enable-static --enable-shared --host=$HOST --target=android"
export CXX="${CROSS_COMPILE}g++ --sysroot=${SYSROOT}"
export LDFLAGS=" -L$SYSROOT/usr/lib $CFLAGS "
export CXXFLAGS=$CFLAGS
export CFLAGS=$CFLAGS
export CC="${CROSS_COMPILE}gcc --sysroot=${SYSROOT}"
export AR="${CROSS_COMPILE}ar"
export LD="${CROSS_COMPILE}ld"
export AS="${CROSS_COMPILE}gcc"
./configure $FLAGS \
--disable-frontend \
--prefix=$PREFIX
$ADDITIONAL_CONFIGURE_FLAG
make clean
make -j8
make install
cd ..
開始編譯命令
//編譯單個平臺
bash build_lame.sh armeabi-v7a
//編譯全平臺
bash build_lame_all
輸出如下：
工程實踐
基於之前的專案工程
新建CMakeLists.txt檔案
cmake_minimum_required(VERSION 3.4.1)
add_library(lame-encode
SHARED
src/main/cpp/lame_encode.cpp
src/main/cpp/mp3_encode.cpp)
find_library(log-lib
log)
find_library(android-lib
android)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=gnu++11")
set(CMAKE_VERBOSE_MAKEFILE on)
add_library(mp3-lame
SHARED
IMPORTED)
set_target_properties(mp3-lame
PROPERTIES IMPORTED_LOCATION
${CMAKE_SOURCE_DIR}/libs/${ANDROID_ABI}/libmp3lame.so
)
#標頭檔案
include_directories(${CMAKE_SOURCE_DIR}/libs/${ANDROID_ABI}/include)
target_link_libraries(lame-encode mp3-lame ${log-lib} ${android-lib})
新建LameEncoder.java檔案
public class LameEncoder {
static {
System.loadLibrary("lame-encode");
}
public native void encode(String pcmPath, String mp3Path, int sampleRate, int channels, int bitRate);
public native void destroy();
}
新建MP3的編碼實現類：mp3_encode.cpp
#include "mp3_encode.h"
Mp3Encoder::Mp3Encoder() {
pcmFile = NULL;
mp3File = NULL;
}
Mp3Encoder::~Mp3Encoder() {
}
int Mp3Encoder::Init(const char *pcmPath, const char *mp3Path,
int sampleRate,
int channels,
int bitRate) {
int result = -1;
pcmFile = fopen(pcmPath, "rb");
if (NULL != pcmFile) {
mp3File = fopen(mp3Path, "wb");
if (NULL != mp3File) {
lameClient = lame_init();
//設定取樣率
lame_set_in_samplerate(lameClient, sampleRate);
lame_set_out_samplerate(lameClient, sampleRate);
lame_set_num_channels(lameClient, channels);
lame_set_brate(lameClient, bitRate / 1000);
lame_set_quality(lameClient, 2);
//初始化引數
lame_init_params(lameClient);
result = 0;
}
}
return result;
}
void Mp3Encoder::Encode() {
int bufferSize = 1024 * 256;
short *buffer = new short[bufferSize / 2];
short *leftBuffer = new short[bufferSize / 4];
short *rightBuffer = new short[bufferSize / 4];
unsigned char *mp3_buffer = new unsigned char[bufferSize];
size_t readBufferSize = 0;
while ((readBufferSize = fread(buffer, 2, bufferSize / 2, pcmFile)) > 0) {
for (int i = 0; i < readBufferSize; i++) {
if (i % 2 == 0) {
leftBuffer[i / 2] = buffer[i];
} else {
rightBuffer[i / 2] = buffer[i];
}
}
size_t wroteSize = lame_encode_buffer(lameClient, leftBuffer, rightBuffer,
(int) (readBufferSize / 2), mp3_buffer, bufferSize);
fwrite(mp3_buffer, 1, wroteSize, mp3File);
}
delete[] buffer;
delete[] leftBuffer;
delete[] rightBuffer;
delete[] mp3_buffer;
}
void Mp3Encoder::Release() {
if (pcmFile) {
fclose(pcmFile);
}
if (mp3File) {
fclose(mp3File);
lame_close(lameClient);
}
}
新建JNI的介面實現類：lame_encode.cpp
#include <jni.h>
#include <stdio.h>
#include "lame_encode.h"
#include "mp3_encode.h"
/**
* 動態註冊
*/
JNINativeMethod methods[] = {
{"encode", "(Ljava/lang/String;Ljava/lang/String;III)V", (void *) encode},
{"destroy", "()V", (void *) destroy}
};
/**
* 動態註冊
* @param env
* @return
*/
jint registerNativeMethod(JNIEnv *env) {
jclass cl = env->FindClass("com/onzhou/audio/lame/LameEncoder");
if ((env->RegisterNatives(cl, methods, sizeof(methods) / sizeof(methods[0]))) < 0) {
return -1;
}
return 0;
}
/**
* 載入預設回撥
* @param vm
* @param reserved
* @return
*/
jint JNI_OnLoad(JavaVM *vm, void *reserved) {
JNIEnv *env = NULL;
if (vm->GetEnv((void **) &env, JNI_VERSION_1_6) != JNI_OK) {
return -1;
}
//註冊方法
if (registerNativeMethod(env) != JNI_OK) {
return -1;
}
return JNI_VERSION_1_6;
}
Mp3Encoder *encoder = NULL;
JNIEXPORT void JNICALL encode(JNIEnv *env, jobject obj, jstring pcmFilePath, jstring mp3FilePath, jint sampleRate,
jint channels,
jint bitRate) {
const char *pcmPath = env->GetStringUTFChars(pcmFilePath, NULL);
const char *mp3Path = env->GetStringUTFChars(mp3FilePath, NULL);
encoder = new Mp3Encoder();
encoder->Init(pcmPath, mp3Path, sampleRate, channels, bitRate);
//開始編碼
encoder->Encode();
env->ReleaseStringUTFChars(pcmFilePath, mp3Path);
env->ReleaseStringUTFChars(mp3FilePath, pcmPath);
}
JNIEXPORT void JNICALL destroy(JNIEnv * env, jobject obj) {
if (NULL != encoder) {
encoder->Release();
encoder = NULL;
}
}
在啟動的LameEncodeActivity中點選按鈕實現功能如下：
Schedulers.newThread().scheduleDirect(new Runnable() {
@Override
public void run() {
File pcmFile = new File(getExternalFilesDir(null), "input.pcm");
File mp3File = new File(getExternalFilesDir(null), "output.mp3");
mLameEncoder = new LameEncoder();
mLameEncoder.encode(pcmFile.getAbsolutePath(), mp3File.getAbsolutePath(), 44100, 2, 128);
}
});
輸出目錄
播放正常，表示編碼正常。
參考： 《音視訊開發進階指南》