转自:https://www.cnblogs.com/renhui/p/9177025.html
一、LAME简介
LAME是目前非常优秀的一种MP3编码引擎,在业界,转码成Mp3格式的音频文件时,最常用的就是LAME库。当达到320Kbit/s时,LAME编码出来的音频质量几乎可以和CD的音质相媲美,并且还能保证整个音频文件的体积非常小,因此若要在移动端平台上编码MP3文件,使用LAME便成为唯一的选择。
二、使用场景
操作系统:Android。
场景:1.录音时保存Mp3格式的文件 2. 将wav无损音频文件转码成mp3这种体积相对较小的音频文件。 3.可以将获取到的音频流进行录制保存为mp3格式。
附:如何录制wav文件,在之前的博客里面我们讲过:Android 音视频开发(二):使用 AudioRecord 采集音频PCM并保存到文件
三、开发准备
LAME的源码是托管到sourceforge.net上的,我们开发一个基于LAME的项目,就不得不下载其源码用于编译。
LAME主页:http://lame.sourceforge.net/
LAME下载:http://sourceforge.net/projects/lame/files/lame/3.99/
本人将源码下载下来了,并上传到百度云了,https://pan.baidu.com/s/1ReepIBAHivnBzMCY5TJDWw,供大家下载参考。
如果需要集成到Android系统上,就需要开发者具备一些NDK开发的能力。
四、开发过程
定义在java类中定义native方法:
private static native long nInit(int inSampleRate, int inChannels, int outSampleRate, int outBitrate, int model, int quality); private static native int nGetVersion(long lamePtr); private static native int mGetMp3bufferSize(long lamePtr); private static native int mGetMp3bufferSizeWithSamples(long lamePtr, int samples); private static native int nEncodeShortInterleaved(long lamePtr, short[] bufLR, int samples, byte[] outMp3buf); private static native int nEncodeShort(long lamePtr, short[] bufL, short[] bufR, int samples, byte[] outMp3buf); private static native int nFlush(long lamePtr, byte[] outBuf); private static native void nClose(long lamePtr);
生成相应的.h的头文件,并实现该头文件,完成整体逻辑的编写。
#include <jni.h> #include <cwchar> #include <math.h> #include "com_renhui_lame_Lame.h" #include "libmp3lame/lame.h" extern "C" JNIEXPORT jlong JNICALL Java_com_renhui_lame_Lame_nInit(JNIEnv *env, jclass type, jint inSampleRate, jint inChannels, jint outSampleRate, jint outBitrate, jint model, jint quality) { lame_global_flags *lameFlags; lameFlags = lame_init(); lame_set_in_samplerate(lameFlags, inSampleRate); lame_set_num_channels(lameFlags, inChannels); lame_set_out_samplerate(lameFlags, outSampleRate); lame_set_brate(lameFlags, outBitrate); lame_set_mode(lameFlags, (MPEG_mode) model); lame_set_quality(lameFlags, quality); int code = lame_init_params(lameFlags); if (code != 0) { lame_close(lameFlags); return code; } return (long) lameFlags; } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_nGetVersion(JNIEnv *env, jclass type, jlong lamePtr) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; return lame_get_version(lameFlags); } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_mGetMp3bufferSize(JNIEnv *env, jclass type, jlong lamePtr) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; return lame_get_size_mp3buffer(lameFlags); } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_mGetMp3bufferSizeWithSamples(JNIEnv *env, jclass type, jlong lamePtr, jint samples) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; int version = lame_get_version(lameFlags); int bitrate = lame_get_brate(lameFlags); int sampleRate = lame_get_out_samplerate(lameFlags); float p = (bitrate / 8.0f) / sampleRate; if (version == 0) { // MPEG2: num_samples*(bitrate/8)/samplerate + 4*576*(bitrate/8)/samplerate + 256 return (jint) ceil(samples * p + 4 * 576 * p + 256); } else if (version == 1) { // MPEG1: num_samples*(bitrate/8)/samplerate + 4*1152*(bitrate/8)/samplerate + 512 return (jint) ceil(samples * p + 4 * 1152 * p + 512); } else { return (jint) ceil((1.25 * samples + 7200)); } } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_nEncodeShortInterleaved(JNIEnv *env, jclass type, jlong lamePtr, jshortArray bufLR_, jint samples, jbyteArray outMp3buf_) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; jshort *bufLR = env->GetShortArrayElements(bufLR_, NULL); jbyte *outMp3buf = env->GetByteArrayElements(outMp3buf_, NULL); const jsize outMp3bufSize = env->GetArrayLength(outMp3buf_); int result = lame_encode_buffer_interleaved(lameFlags, bufLR, samples, (u_char *) outMp3buf, outMp3bufSize); env->ReleaseShortArrayElements(bufLR_, bufLR, 0); env->ReleaseByteArrayElements(outMp3buf_, outMp3buf, 0); return result; } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_nEncodeShort(JNIEnv *env, jclass type, jlong lamePtr, jshortArray bufL_, jshortArray bufR_, jint samples, jbyteArray outMp3buf_) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; jshort *bufL = env->GetShortArrayElements(bufL_, NULL); jshort *bufR = env->GetShortArrayElements(bufR_, NULL); jbyte *outMp3buf = env->GetByteArrayElements(outMp3buf_, NULL); const jsize outMp3bufSize = env->GetArrayLength(outMp3buf_); int result = lame_encode_buffer(lameFlags, bufL, bufR, samples, (u_char *) outMp3buf, outMp3bufSize); env->ReleaseShortArrayElements(bufL_, bufL, 0); env->ReleaseShortArrayElements(bufR_, bufR, 0); env->ReleaseByteArrayElements(outMp3buf_, outMp3buf, 0); return result; } JNIEXPORT jint JNICALL Java_com_renhui_lame_Lame_nFlush(JNIEnv *env, jclass type, jlong lamePtr, jbyteArray outBuf_) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; jbyte *outBuf = env->GetByteArrayElements(outBuf_, NULL); const jsize outBufSize = env->GetArrayLength(outBuf_); int result = lame_encode_flush(lameFlags, (u_char *) outBuf, outBufSize); env->ReleaseByteArrayElements(outBuf_, outBuf, 0); return result; } JNIEXPORT void JNICALL Java_com_renhui_lame_Lame_nClose(JNIEnv *env, jclass type, jlong lamePtr) { lame_global_flags *lameFlags; lameFlags = (lame_global_flags *) lamePtr; lame_close(lameFlags); }
编写Android.mk和Application.mk,为ndk-build打包做准备。
Android.mk:
LOCAL_PATH := $(call my-dir) include $(CLEAR_VARS) LOCAL_MODULE :=mp3lame LAME_LIBMP3_DIR :=libmp3lame LOCAL_SRC_FILES :=\ $(LAME_LIBMP3_DIR)/bitstream.c \ $(LAME_LIBMP3_DIR)/fft.c \ $(LAME_LIBMP3_DIR)/id3tag.c \ $(LAME_LIBMP3_DIR)/mpglib_interface.c \ $(LAME_LIBMP3_DIR)/presets.c \ $(LAME_LIBMP3_DIR)/quantize.c \ $(LAME_LIBMP3_DIR)/reservoir.c \ $(LAME_LIBMP3_DIR)/tables.c \ $(LAME_LIBMP3_DIR)/util.c \ $(LAME_LIBMP3_DIR)/VbrTag.c \ $(LAME_LIBMP3_DIR)/encoder.c \ $(LAME_LIBMP3_DIR)/gain_analysis.c \ $(LAME_LIBMP3_DIR)/lame.c \ $(LAME_LIBMP3_DIR)/newmdct.c \ $(LAME_LIBMP3_DIR)/psymodel.c \ $(LAME_LIBMP3_DIR)/quantize_pvt.c \ $(LAME_LIBMP3_DIR)/set_get.c \ $(LAME_LIBMP3_DIR)/takehiro.c \ $(LAME_LIBMP3_DIR)/vbrquantize.c \ $(LAME_LIBMP3_DIR)/version.c \ com_renhui_lame_Lame.cpp LOCAL_C_INCLUDES += $(LOCAL_PATH)/mp3lame LOCAL_LDLIBS := -llog -lz include $(BUILD_SHARED_LIBRARY)
Application.mk:
APP_ABI := all #APP_ABI := armeabi armeabi-v7a x86 # APP_ABI :=armeabi APP_PLATFORM := android-14
附:有关编译语法,整理了一篇文章,供大家参考:Android NDK学习(二):编译脚本语法Android.mk和Application.mk。
五、思维拓展
1. 录音为Mp3格式
https://github.com/renhui/LameAndroid-master
2. 结合NBPlayer,将Player的PCM数据保存到Mp3文件里
TODO:在NBPlayer里面,我们应该是可以获取到PCM的数据的。