我试图使一个简单的C程序播放AIFF或WAV文件。根据我在http://www.xiph.org/ao/doc/上看到的内容，这应该可以工作，但是无论我输入什么文件，它都会发出嗡嗡声。这怎么了
/* compile with "gcc -o playme playme.c -lao -ldl -lm" */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ao/ao.h>
#include <math.h>
ao_device *device;
ao_sample_format format;
int main(int argc, char *argv[])
{
int default_driver;
char *buffer;
unsigned long count;
FILE *fp;
if (argc != 2) {
printf("usage: %s <filename>\n", argv[0]);
exit(1);
}
ao_initialize();
default_driver = ao_default_driver_id();
memset(&format, 0, sizeof(format));
format.bits = 16;
format.channels = 2;
format.rate = 44100;
format.byte_format = AO_FMT_LITTLE;
device = ao_open_live(default_driver, &format, NULL /* no options */);
if (device == NULL) {
printf("Error opening sound device.\n");
exit(1);
}
fp = fopen(argv[1], "rb");
if (fp == NULL) {
printf("Cannot open %s.\n", argv[1]);
exit(2);
}
fseek(fp, 0, SEEK_END);
count = ftell(fp);
fseek(fp, 0, SEEK_SET);
fread(buffer, sizeof(char), count, fp);
ao_play(device, buffer, count);
ao_close(device);
ao_shutdown();
return 0;
}
我没有意识到的一个关键问题是，libao绝对不解码。因此，程序员应在打开音频设备之前提取样本大小，速率，通道等，并将其馈送到libao。libsndfile可用于执行此操作，但是如果您只想快速又脏一些，请使用下面的代码来播放AIFF文件：
/* compile with "gcc -o playaiff playaiff.c -lao -ldl -lm" */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ao/ao.h>
#include <math.h>
#define MAXCHAN 8
ao_device *device;
ao_sample_format format;
#define gshort( b) (((int)((b)[0]) << 8) + (int)((b)[1]))
#define glong( b) (((int)((b)[0]) << 24) + ((int)((b)[1]) << 16) +\
((int)((b)[2]) << 8) + (int)((b)[3]))
typedef struct {
short channels;
short samplesize;
int samplerate;
unsigned long samplecount;
int valid;
} aiffinfo;
aiffinfo getaiffinfo(FILE *);
static int IeeeExtendedToLong(unsigned char *);
int main(int argc, char *argv[])
{
int default_driver;
char *buffer;
aiffinfo info;
FILE *fp;
if (argc != 2) {
printf("usage: %s <filename>\n", argv[0]);
exit(1);
}
ao_initialize();
default_driver = ao_default_driver_id();
memset(&format, 0, sizeof(format));
fp = fopen(argv[1], "rb");
if (fp == NULL) {
printf("Cannot open %s.\n", argv[1]);
exit(2);
}
info = getaiffinfo(fp);
if (!info.valid) {
printf("Invalid AIFF file.\n");
exit(1);
}
format.bits = info.samplesize;
format.channels = info.channels;
format.rate = info.samplerate;
format.byte_format = AO_FMT_LITTLE;
device = ao_open_live(default_driver, &format, NULL /* no options */);
if (device == NULL) {
printf("Error opening sound device.\n");
exit(1);
}
buffer = malloc(sizeof(char) * info.samplecount);
fread(buffer, sizeof(char), info.samplecount, fp);
ao_play(device, buffer, info.samplecount);
ao_close(device);
ao_shutdown();
return 0;
}
aiffinfo getaiffinfo(FILE *fp)
{
int size;
int len;
int offset;
int blocksize;
int found = 0;
unsigned char chunk[18];
unsigned char fid[4];
aiffinfo info;
info.samplesize = 0;
info.valid = 0;
if (fread(chunk, 1, 4, fp) < 4) return info;
if (memcmp(chunk,"FORM",4)) return info;
if (fread(chunk, 1, 4, fp) < 4) return info;
size = glong(chunk);
if (size & 1) size++;
if (size < 20) return info;
if (fread(chunk, 1, 4, fp) < 4) return info;
if (memcmp(chunk, "AIFF", 4)) return info;
size -= 4;
while (size > 8) {
if (fread(fid, 1, 4, fp) < 4) return info; // chunck id
if (fread(chunk, 1, 4, fp) < 4) return info; // and len
size -= 8;
len = glong(chunk);
if (len < 0) return info;
if (len & 1) len++;
size -= len;
if (size < 0) return info;
if (memcmp(fid, "COMM", 4) == 0) {
if (len != 18) return info;
if (fread(chunk, 1, 18, fp) < 18) return info;
info.channels = gshort(chunk);
if (info.channels < 1) return info;
if (info.channels > MAXCHAN) return info;
info.samplecount = glong(chunk+2);
if (info.samplecount < 1) return info;
info.samplerate = IeeeExtendedToLong(chunk + 8);
if (info.samplerate <= 0) return info;
info.samplesize = gshort(chunk + 6);
if (info.samplesize < 1 || info.samplesize > 16) return info;
} else if (memcmp(fid,"SSND",4)==0){
if (!info.channels) return info;
if (fread(chunk, 1, 4, fp) < 4) return info;
offset = glong(chunk);
if (fread(chunk, 1, 4, fp) < 4) return info;
blocksize = glong(chunk);
if (blocksize) return info;
if (offset) fseek(fp, offset,SEEK_CUR);
found = 1;
break;
} else fseek (fp, len, SEEK_CUR);
}
if (!found) return info;
if (!info.channels) return info;
// printf("Looks good so far.\n");
info.valid = 1;
return info;
}
/****************************************************************
* Extended precision IEEE floating-point conversion routine.
****************************************************************/
#ifndef Uint32
#define Uint32 unsigned int
#endif
#ifndef HUGE_INT32
#define HUGE_INT32 0x7fffffff
#endif /* HUGE_VAL */
static int IeeeExtendedToLong( unsigned char *bytes)
{
int f = 0;
int expon;
Uint32 hiMant;
Uint32 loMant;
expon = ((bytes[0] & 0x7F) << 8) | (bytes[1] & 0xFF);
hiMant = ((Uint32) (bytes[2] & 0xFF) << 24)
| ((Uint32) (bytes[3] & 0xFF) << 16)
| ((Uint32) (bytes[4] & 0xFF) << 8)
| ((Uint32) (bytes[5] & 0xFF));
loMant = ((Uint32) (bytes[6] & 0xFF) << 24)
| ((Uint32) (bytes[7] & 0xFF) << 16)
| ((Uint32) (bytes[8] & 0xFF) << 8)
| ((Uint32) (bytes[9] & 0xFF));
if (expon == 0 && hiMant == 0 && loMant == 0) f = 0;
else if (expon == 0x7FFF) f = HUGE_INT32;
else {
expon -= 16382;
expon = 32-expon;
if (expon < 0) f = HUGE_INT32;
else f = hiMant >> expon;
}
if (bytes[0] & 0x80)
return -f;
else
return f;
}
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