使用C语言扩展Python(三)

上一篇中我们已经了解如何在Python程序和C模块之间进行值的相互传递，现在我们来进入实作阶段，看看如何将一个C语言开发的开源mp3编解码库LAME包装为一个Python下可以使用的扩展模块。

首先去http://lame.sourceforge.net/download.php下载LAME的源代码，然后切换到root用户编译源代码，

./configure
make
make install

安装完成后你可以在/usr/local/include/lame目录下找到lame.h头文件，我们在后面的demo程序中会include它的，下面就是一个非常简单的lame示例程序lame_test.c:

#include <stdio.h>
#include <stdlib.h>
#include <lame.h>

#define INBUFSIZE 4096
#define MP3BUFSIZE (int) (1.25 * INBUFSIZE) + 7200

int encode(char* inPath, char* outPath) {
    int status = 0;
    lame_global_flags* gfp;
    int ret_code;
    FILE* infp;
    FILE* outfp;
    short* input_buffer;
    int input_samples;
    char* mp3_buffer;
    int mp3_bytes;
    
    gfp = lame_init();
    if (gfp == NULL) {
        printf("lame_init failed\n");
        status = -1;
        goto exit;
    }
    
    ret_code = lame_init_params(gfp);
    if (ret_code < 0) {
        printf("lame_init_params returned %d\n",ret_code);
        status = -1;
        goto close_lame;
    }

    infp = fopen(inPath, "rb");
    outfp = fopen(outPath, "wb");
    
    input_buffer = (short*)malloc(INBUFSIZE*2);
    mp3_buffer = (char*)malloc(MP3BUFSIZE);
    
    do{
        input_samples = fread(input_buffer, 2, INBUFSIZE, infp);
        mp3_bytes = lame_encode_buffer_interleaved(gfp, input_buffer,input_samples/2, mp3_buffer, MP3BUFSIZE);
        if (mp3_bytes < 0) {
            printf("lame_encode_buffer_interleaved returned %d\n", mp3_bytes);
            status = -1;
            goto free_buffers;
        } else if(mp3_bytes > 0) {
            fwrite(mp3_buffer, 1, mp3_bytes, outfp);
        }
    }while (input_samples == INBUFSIZE);
    
    mp3_bytes = lame_encode_flush(gfp, mp3_buffer, sizeof(mp3_buffer));
    if (mp3_bytes > 0) {
        printf("writing %d mp3 bytes\n", mp3_bytes);
        fwrite(mp3_buffer, 1, mp3_bytes, outfp);
    }
free_buffers:
    free(mp3_buffer);
    free(input_buffer);
    
    fclose(outfp);
    fclose(infp);
close_lame:
    lame_close(gfp);
exit:
    return status;
}

int main(int argc, char** argv) {
    if (argc < 3) {
        printf("usage: lame_test rawinfile mp3outfile\n");
    }
    encode(argv[1], argv[2]);
    return 0;
}

编译步骤：

gcc -I /usr/local/include/lame lame_test.c -lmp3lame -o lame_test

试验准备：

首先需要一个test.wav文件，先安装sox来将wav文件转为raw格式的数据：

    sudo apt-get install sox
    sox test.wav -t raw test.raw

 

然后执行lame_test来对其进行mp3编码:

./lame_test ./test.raw ./test.mp3 

好了，现在我们要在这个c程序的基础上将其包装为一个Python扩展模块。下面的pylame.c就是简单地调用lame_test.c中定义的encode方法，然后通过它对外部的python程序提高mp3编码的服务

#include <Python.h>
#include <lame.h>

int encode(char* ,char*);

static PyObject * pylame_encode(PyObject* self, PyObject* args) {
    int status;
    char* inPath;
    char* outPath;
    if (!PyArg_ParseTuple(args, "ss", &inPath, &outPath)) {        
        return NULL;
    }
    status = encode(inPath, outPath);
    return Py_BuildValue("i", status);
}

static PyMethodDef pylame_methods[] = {
    {"encode", pylame_encode, METH_VARARGS, NULL},
    {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC initpylame() {
    Py_InitModule3("pylame", pylame_methods, "an simple lame module.");
}

模块编译步骤：

gcc -shared -I /usr/include/python2.6 -I /usr/local/include/lame/ pylame.c lame_test.c -lmp3lame -o pylame.so

ok,现在lame扩展模块已经封装好了，可以到python程序中进行调用了。在pylame.so所在目录下新建一个python文件lame1.py代码如下：

import pylame

if __name__ == '__main__':
    inPath = './test.raw'
    outPath = './test.mp3'
    pylame.encode(inPath, outPath)

编译执行： 

python ./lame1.py

你会发现生成了一个test.mp3,打开听听看是否是你想要的歌曲呢，呵呵。。。