mp3文件的时长
有没有什么简单的方法可以知道一个mp3文件的长度（以秒为单位），而不使用外部库? （如果能提供Python代码就更好了）
6 个回答
8
简单地说，就是用Python解析MP3的二进制数据来计算一些东西。
这听起来有点难。我不太懂Python，不过我有一些从我之前写的另一个程序中整理出来的代码。
注意：这段代码是用C++写的（抱歉，这是我能提供的）。而且，这段代码只能处理恒定比特率的MPEG 1 音频层3文件。大多数情况下应该可以用，但我不能保证在所有情况下都能正常工作。希望这段代码能满足你的需求，也希望把它改写成Python比从头开始写要简单。
// determines the duration, in seconds, of an MP3;
// assumes MPEG 1 (not 2 or 2.5) Audio Layer 3 (not 1 or 2)
// constant bit rate (not variable)
#include <iostream>
#include <fstream>
#include <cstdlib>
using namespace std;
//Bitrates, assuming MPEG 1 Audio Layer 3
const int bitrates[16] = {
0, 32000, 40000, 48000, 56000, 64000, 80000, 96000,
112000, 128000, 160000, 192000, 224000, 256000, 320000, 0
};
//Intel processors are little-endian;
//search Google or see: http://en.wikipedia.org/wiki/Endian
int reverse(int i)
{
int toReturn = 0;
toReturn |= ((i & 0x000000FF) << 24);
toReturn |= ((i & 0x0000FF00) << 8);
toReturn |= ((i & 0x00FF0000) >> 8);
toReturn |= ((i & 0xFF000000) >> 24);
return toReturn;
}
//In short, data in ID3v2 tags are stored as
//"syncsafe integers". This is so the tag info
//isn't mistaken for audio data, and attempted to
//be "played". For more info, have fun Googling it.
int syncsafe(int i)
{
int toReturn = 0;
toReturn |= ((i & 0x7F000000) >> 24);
toReturn |= ((i & 0x007F0000) >> 9);
toReturn |= ((i & 0x00007F00) << 6);
toReturn |= ((i & 0x0000007F) << 21);
return toReturn;
}
//How much room does ID3 version 1 tag info
//take up at the end of this file (if any)?
int id3v1size(ifstream& infile)
{
streampos savePos = infile.tellg();
//get to 128 bytes from file end
infile.seekg(0, ios::end);
streampos length = infile.tellg() - (streampos)128;
infile.seekg(length);
int size;
char buffer[3] = {0};
infile.read(buffer, 3);
if( buffer[0] == 'T' && buffer[1] == 'A' && buffer[2] == 'G' )
size = 128; //found tag data
else
size = 0; //nothing there
infile.seekg(savePos);
return size;
}
//how much room does ID3 version 2 tag info
//take up at the beginning of this file (if any)
int id3v2size(ifstream& infile)
{
streampos savePos = infile.tellg();
infile.seekg(0, ios::beg);
char buffer[6] = {0};
infile.read(buffer, 6);
if( buffer[0] != 'I' || buffer[1] != 'D' || buffer[2] != '3' )
{
//no tag data
infile.seekg(savePos);
return 0;
}
int size = 0;
infile.read(reinterpret_cast<char*>(&size), sizeof(size));
size = syncsafe(size);
infile.seekg(savePos);
//"size" doesn't include the 10 byte ID3v2 header
return size + 10;
}
int main(int argCount, char* argValues[])
{
//you'll have to change this
ifstream infile("C:/Music/Bush - Comedown.mp3", ios::binary);
if(!infile.is_open())
{
infile.close();
cout << "Error opening file" << endl;
system("PAUSE");
return 0;
}
//determine beginning and end of primary frame data (not ID3 tags)
infile.seekg(0, ios::end);
streampos dataEnd = infile.tellg();
infile.seekg(0, ios::beg);
streampos dataBegin = 0;
dataEnd -= id3v1size(infile);
dataBegin += id3v2size(infile);
infile.seekg(dataBegin,ios::beg);
//determine bitrate based on header for first frame of audio data
int headerBytes = 0;
infile.read(reinterpret_cast<char*>(&headerBytes),sizeof(headerBytes));
headerBytes = reverse(headerBytes);
int bitrate = bitrates[(int)((headerBytes >> 12) & 0xF)];
//calculate duration, in seconds
int duration = (dataEnd - dataBegin)/(bitrate/8);
infile.close();
//print duration in minutes : seconds
cout << duration/60 << ":" << duration%60 << endl;
system("PAUSE");
return 0;
}
11
为了帮助谷歌的关注者，这里有一些额外的外部库：
mpg321 -t
ffmpeg -i
midentify（基本上是mplayer）请参见 使用mplayer来确定音频/视频文件的长度
mencoder（传入无效参数，它会输出错误信息，但也会给你关于文件的信息，比如 $ mencoder inputfile.mp3 -o fake）
mediainfo 程序 http://mediainfo.sourceforge.net/en
exiftool
Linux 的 "file" 命令
mp3info
sox
参考资料：
（把这个做成一个维基，方便其他人添加内容）。
还有一些库：.net: naudio，java: jlayer，c: libmad
谢谢！