擷取 音樂的方法

最近我被要求擷取某網站的背景音樂，該網站十分狡猾，如果你用 Windows Media Player 去開啟以下的link: http://m2.colorme.com.cn/ftp/l/l/h/8/llh8/music/1168884738897.wma 《滇聆》雪境，可以收聽的，但用其他方法下載該音樂，它卻回應一些無關痛癢的網頁。結果我要寫下面的程式，去扮「我是音樂播放器」才能下載 :

編譯: gcc -l curl -o test test.c
用法: ./test http://m2.colorme.com.cn/ftp/l/l/h/8/llh8/music/1168884738897.wma > /tmp/1.wma


程式碼如下
#include
#include
#include
#include
#include
#include

#define ICY_METAINT "icy-metaint:"

static int metaint, metacnt, metalen_left;
static int load_from_net_so_far;

// If it is 8192, you always get 8192 bytes of real data, followed by the metadata.
// The meta data format is mlength (1 byte), followed by string (variable length).
// The length of the string is the mlength multiplied by 16.
// So when there is no metadata, you'll get a single byte (mlength=0).
static int
head_write_callback(void *buffer, size_t size, size_t nmemb, void *stream) {
int size_to_write=size*nmemb;
char *p;

fwrite(buffer, size, nmemb, stderr);

if ((p=strstr(buffer, ICY_METAINT))!=NULL) {
metaint=atoi(p+strlen(ICY_METAINT));
}

return size_to_write;
}

static int
play_audio(char *buffer, size_t size, size_t nmemb, void *stream) {
fwrite(buffer, size, nmemb, stdout);
load_from_net_so_far+=size*nmemb;
fprintf(stderr, "\b\b\b\b\b\b\b\b\b\b%010d", load_from_net_so_far);
return size*nmemb;
}

int
main(int argc, char **argv) {
CURL *curl=NULL;
CURLcode ret;
struct curl_slist *headerlist = NULL;
struct curl_slist *aliases = NULL; // Yick_2003_12_29
char *url;

if (argc!=2) {
fprintf(stderr, "%s url\n", argv[0]);
fprintf(stderr, "where url can be a playlist or mp3 url\n");
fprintf(stderr, "the song will appear at stdout\n");

fprintf(stderr, "%s \"http://www.shoutcast.com/sbin/shoutcast-playlist.pls?rn=911919&file=filename.pls\" &\n", argv[0]);
fprintf(stderr, "%s \"http://www.shoutcast.com/sbin/shoutcast-playlist.pls?rn=1704&file=filename.pls\" &\n", argv[0]);
fprintf(stderr, "%s \"http://m2.colorme.com.cn/ftp/l/l/h/8/llh8/music/1168884738897.wma\" 1> /tmp/1.wma \n", argv[0]);
return -1;
}

url=argv[1];

metaint=8192;
metacnt=0;
metalen_left=0;
load_from_net_so_far=0;

curl = curl_easy_init();

headerlist = curl_slist_append(headerlist, "Pragma: stream-switch-entry=ffff:1:0");
headerlist = curl_slist_append(headerlist, "Pragma: stream-switch-count=1");
headerlist = curl_slist_append(headerlist, "Pragma: xClientGUID={71F1B2A2-87F5-11D5-A064-0050DA8DAD15}");
headerlist = curl_slist_append(headerlist, "Pragma: xPlayStrm=1");
headerlist = curl_slist_append(headerlist, "Pragma: no-cache,rate=1.000000,request-context=2");
headerlist = curl_slist_append(headerlist, "Icy-MetaData: 1");
headerlist = curl_slist_append(headerlist, "Accept: */*");
headerlist = curl_slist_append(headerlist, "Accept-Encoding: deflate");
headerlist = curl_slist_append(headerlist, "Connection: keep-alive");
headerlist = curl_slist_append(headerlist, "TE: trailers,deflate");
aliases = curl_slist_append(aliases, "ICY 200 OK" );

curl = curl_easy_init();

if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, url);
curl_easy_setopt(curl, CURLOPT_USERAGENT, "NSPlayer/4.1.0");
curl_easy_setopt(curl, CURLOPT_HTTPHEADER, headerlist);
curl_easy_setopt(curl, CURLOPT_FAILONERROR, 1);
curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1);
curl_easy_setopt(curl, CURLOPT_HTTP200ALIASES, aliases);
curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, play_audio);
curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, head_write_callback);
curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 5);
ret=curl_easy_perform(curl);

if (load_from_net_so_far) {
fprintf(stderr, "audio ended\n");
goto SRC_SHOUTCAST_THREAD_FN_LBL;
} else {
fprintf(stderr, "Error in opening url %s\n", url);
}
curl_easy_cleanup(curl);
curl=NULL;
}

SRC_SHOUTCAST_THREAD_FN_LBL:

if (curl)
curl_easy_cleanup(curl);

return NULL;
}