Linux下的OSS音频接口编程一例
采用OSS进行音频编程时应当遵循的一般性框架：
（1）打开音频设备；
（2）设置采样格式（即量化位数）；
（3）设置声道数（单声道或者立体声）；
（4）设置采样率（即采样速度）；
（5）从设备读入数据或者向设备写入数据；
（6）关闭音频设备；
上述过程中，第（6）可选，因为在进程正常或非正常退出时都会关闭它所打开的文件描述字，这样也就把音频设备的资源释放了。但是，除此之外的五个步骤是不能缺少的，并且顺序也不能颠倒（OSS编程指南对此的说明是：在指定声道数之前设置采样率不能在所有的音频硬件上工作——如果在将声卡设置为高采样率模式之后更改了声道数，应用程序将出现不正确的行为。同时，必须在使用read()或者write()调用读写数据之前设置采样率）。
这是作者编写的一个读写/dev/dsp设备的小程序，可以用它来录制一段声音，也可以用来将录制到文件中的声音播放出来。除此之外，还可以通过命令行参数指定设备参数，如：采样率、量化位数、声道数、要录制的声音长度，等等。详细的命令行参数解释如下：
SndKit [-h] [-d device] [-c channel] [-b bits] [-f hz] [-l len] <-r|-p file>
其中：
¨ -h：打印帮助信息；
¨ -d：指定要读写的音频设备（默认为/dev/dsp）；
¨ -c：指定使用的声道数（默认为MONO，单声道）；
¨ -b：指定量化位数（默认为8位无符号整数）；
¨ -f：指定采样频率（默认为8KHz）；
¨ -l：指定录制的声音文件的长度（默认为1024，单位为KB）；
¨ -r file：录制声音，file存放录制的声音数据；
¨ -p file：播放file文件中存储的声音数据。
注意：-h，-r，-p这三个选项不能同时出现在命令行上。比如，可以通过下面的命令录制一段声音：
[root@cyc source]# ./SndKit -c 2 -b 16 -f 48 -r cyc.wav
采用的是双声道立体声、16位量化位数、48KHz采样频率、录制的声音保存在cyc.wav文件中，要录制的声音长度采用默认值1024KB。录制好之后，可以通过下面的命令播放出来：
[root@cyc source]# ./SndKit -c 2 -b 16 -f 48 -p cyc.wav
sound data play complete!
需要注意的是，录制时采用的是什么样的参数，播放时就应该采用同样的参数，否则将会出错。
下面直接给出源代码：
/* Name: SndKit.c Copyright: GPLv2 Author: rockins([email protected]) Date: 15-10-06 18:22 Description: implent raw sound record/play run: ./SndKit [-h] [-d device] [-c channel] [-b bits] [-f hz] [-l len] <-r|-p file> e.g.: ./SndKit -h show help information ./SndKit -r record.wav record audio from microphone(/dev/dsp) ./SndKit -d /dev/dsp -p record.wav playback record.wav via /dev/dsp ./SndKit -b 8 -f 22 -r reacord.wav record audio in 8 bit & 22k hz ./SndKit -d /dev/dsp -c 2 -r record.wav record audio in /dev/dsp and stereo ./SndKit -r -l 40 record.wav record 40k audio data */ #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <fcntl.h> #include <errno.h> #include <sys/ioctl.h> #include <linux/soundcard.h> /*for OSS style sound programing */ #define TRUE 1 #define FALSE 0 #define FMT8BITS AFMT_U8 /*unsigned 8 bits(for almost PC) */ #define FMT16BITS AFMT_S16_LE /*signed 16 bits,little endian */ #define FMT8K 8000 /*default sampling rate */ #define FMT11K 11025 /*11,22,44,48 are three pop rate */ #define FMT22K 22050 #define FMT44K 44100 #define FMT48K 48000 #define MONO 1 #define STEREO 2 #define ACT_RECORD 0 #define ACT_PLAY 1 #define DFT_SND_DEV "/dev/dsp" #define DFT_SND_FMT FMT8BITS #define DFT_SND_SPD FMT8K #define DFT_SND_CHN MONO #define DFT_LEN 1024 /*default record length:40k */ #define BUFF_SIZE 512 /*buffer size:512 Bytes */ /************** function prototype ********************/ void Usage(void); int OpenDevice(const char *, unsigned int); int OpenFile(const char *, unsigned int); int CloseDevice(unsigned int); int CloseFile(unsigned int); /************** function implementation **************/ int main(int argc, char *argv[]) { unsigned int snd_fmt = DFT_SND_FMT; /*sound format,bits */ unsigned int snd_chn = DFT_SND_CHN; /*sound channel number */ unsigned int snd_spd = DFT_SND_SPD; /*sound speed,frequency */ unsigned char *s_file = NULL; /*file hold sound data */ unsigned char *snd_device = DFT_SND_DEV; /*sound device */ unsigned int recd_or_play = ACT_PLAY; /*flag(default play) */ unsigned char buff[BUFF_SIZE]; /*sound buffer */ unsigned long len = DFT_LEN * 1024; /*record or play length(k) */ int snd_fd; /*sound device descriptor */ int s_fd; /*sound data file descrit */ ssize_t n; /*bytes already in or out */ ssize_t nRD; /*bytes readin */ ssize_t nWR; /*bytes write out */ unsigned int opt_chr; /*hold cli option */ unsigned int opt_err = FALSE; /*indicate whether parse option error */ /*parse cli option via getopt routine */ optind = 0; /*set optindex to 0 */ while ((opt_chr = getopt(argc, argv, "hd:c:b:f:l:r:p:")) != -1) { switch (opt_chr) { case 'h': Usage(); return (0); /*return, 0 denote success */ break; case 'd': snd_device = optarg; /*sound device name */ break; case 'c': if (atoi(optarg) == 1) /*select channel number */ snd_chn = MONO; else if (atoi(optarg) == 2) snd_chn = STEREO; else { opt_err = 1; /*error occur */ fprintf(stderr, "wrong channel setting," "should be 1 or 2(default 1,MONO)\n"); } break; case 'b': if (atoi(optarg) == 8) /*select data bit */ snd_fmt = FMT8BITS; else if (atoi(optarg) == 16) snd_fmt = FMT16BITS; else { opt_err = 1; /*error occur */ fprintf(stderr, "wrong bits setting," "should be 8 or 16(default 8)\n"); } break; case 'f': if (atoi(optarg) == 8) snd_spd = FMT8K; /*sampling rate:8kbps */ else if (atoi(optarg) == 11) snd_spd = FMT11K; /*smapling rate:11.025k */ else if (atoi(optarg) == 22) snd_spd = FMT22K; /*sampling rate:22.050k */ else if (atoi(optarg) == 44) snd_spd = FMT44K; /*sampling rate:44.100k */ else if (atoi(optarg) == 48) snd_spd = FMT48K; /*sampling rate:48k */ else { opt_err = 1; /*error occur */ fprintf(stderr, "wrong sampling rate," "should be 8,11,22,or 44(default 8kbps)\n"); } break; case 'l': len = atoi(optarg) * 1024; /*record length(k) */ break; case 'r': recd_or_play = ACT_RECORD; s_file = optarg; /*file to record sound */ break; case 'p': recd_or_play = ACT_PLAY; s_file = optarg; /*file to play sound */ break; case '?': opt_err = 1; fprintf(stderr, "unknown option:%c\n", optopt); break; default: opt_err = 1; fprintf(stderr, "getopt error:%d\n", opterr); break; } } /*check if cli option parsed right*/ if (opt_err || argc < 2) { fprintf(stderr, "parse command option failed!!!\n" "run ./SndKit -h for help\n"); return (-1); } /*open device */ if ((snd_fd = OpenDevice(snd_device, recd_or_play)) < 0) { fprintf(stderr, "cannot open device %s:%s\n", snd_device, strerror(errno)); return (-1); } /*open sound data file */ if ((s_fd = OpenFile(s_file, recd_or_play)) < 0) { fprintf(stderr, "cannot open sound file %s:%s\n", s_file, strerror(errno)); return (-1); } /*set sound format */ if (SetFormat(snd_fd, snd_fmt, snd_chn, snd_spd) < 0) { fprintf(stderr, "cannot set %s in bit %d, channel %d, speed %d\n", snd_device, snd_fmt, snd_chn, snd_spd); return (-1); } /*do real action:record or playback */ if (recd_or_play == ACT_RECORD) { /*record sound into data file*/ n = 0; while (n < len) { nRD = 0; /*amount read from sound device */ if ((nRD = read(snd_fd, buff, BUFF_SIZE)) < 0) { perror("read sound device failed"); return (-1); } if (n + nRD <= len) /*the len is not full */ nWR = nRD; /*write amount to sound data file */ else nWR = len - n; /*len will be overflow */ unsigned long old_nWR = nWR; /*s hold nWR's old value */ unsigned long t = 0L; /*temp counter */ while (nWR > 0) { if ((t = write(s_fd, buff, nWR)) < 0) { perror("write sound data file failed"); return (-1); } nWR -= t; } n += old_nWR; } } else if (recd_or_play == ACT_PLAY) { /*write sound data to device*/ while (TRUE) { nRD = 0L; /*read amount from sound device */ if ((nRD = read(s_fd, buff, BUFF_SIZE)) < 0) { perror("read sound data file failed"); return (-1); } else if (nRD == 0) { /*nRD == 0 means all sound stream output */ printf("sound data play complete!\n"); exit(0); } nWR = nRD; while (nWR > 0) { /*write into device*/ if ((n = write(snd_fd, buff, nWR)) < 0) { perror("write sound device file failed"); return (-1); } nWR -= n; } } } /*close sound device and sound data file*/ CloseDevice(snd_fd); CloseFile(s_fd); return (0); } /* * OpenDevice():open sound device * params: * dev_name -- device name,such as /dev/dsp * flag -- flag(ACT_RECORD or ACT_PLAY) * returns: * file descriptor of sound device if sucess * -1 if failed */ int OpenDevice(const char *dev_name, unsigned int flag) { int dev_fd; /*open sound device */ if (flag == ACT_RECORD) { if ((dev_fd = open(dev_name, O_RDONLY)) < 0) { return (-1); } } else if (flag == ACT_PLAY) { if ((dev_fd = open(dev_name, O_WRONLY)) < 0) { return (-1); } } return (dev_fd); } /* * CloseDevice():close the sound device * params: * dev_fd -- the sound device's file descriptor * returns: * 0 if success * -1 if error occured */ int CloseDevice(unsigned int dev_fd) { return (close(dev_fd)); } /* * OpenFile():open sound data file * params: * file_name -- file name,e.g,record.wav * flag -- flag(ACT_RECORD or ACT_PLAY) * returns: * file descriptor of sound data file if sucess * -1 if failed */ int OpenFile(const char *file_name, unsigned int flag) { int file_fd; /*open sound data file */ if (flag == ACT_RECORD) { if ((file_fd = open(file_name, O_WRONLY)) < 0) { return (-1); } } else if (flag == ACT_PLAY) { if ((file_fd = open(file_name, O_RDONLY)) < 0) { return (-1); } } return (file_fd); } /* * CloseFile():close the sound data file * params: * file_fd -- the sound data file's descriptor * returns: * 0 if success * -1 if error occured */ int CloseFile(unsigned int file_fd) { return (close(file_fd)); } /* * SetFormat():Set Record and Playback format * params; * fd -- device file descriptor * chn -- channel(MONO or STEREO) * bits -- FMT8BITS(8bits), FMT16BITS(16bits) * hz -- FMT8K(8000HZ), FMT16K(16000HZ), FMT22K(22000HZ), * FMT44K(44000HZ),FMT48K(48000HZ) * returns: * return 0 if success, else return -1 * notes: * parameter setting order should be like as: * 1.sample format(number of bits) * 2.number of channels(mono or stereo) * 3.sampling rate(speed) */ int SetFormat(unsigned int fd, unsigned int bits, unsigned int chn, unsigned int hz) { int ioctl_val; /* set bit format */ ioctl_val = bits; if (ioctl(fd, SNDCTL_DSP_SETFMT, &ioctl_val) == -1) { fprintf(stderr, "Set fmt to bit %d failed:%s\n", bits, strerror(errno)); return (-1); } if (ioctl_val != bits) { fprintf(stderr, "do not support bit %d, supported %d\n", bits, ioctl_val); return (-1); } /*set channel */ ioctl_val = chn; if ((ioctl(fd, SNDCTL_DSP_CHANNELS, &ioctl_val)) == -1) { fprintf(stderr, "Set Audio Channels %d failed:%s\n", chn, strerror(errno)); return (-1); } if (ioctl_val != chn) { fprintf(stderr, "do not support channel %d,supported %d\n", chn, ioctl_val); return (-1); } /*set speed */ ioctl_val = hz; if (ioctl(fd, SNDCTL_DSP_SPEED, &ioctl_val) == -1) { fprintf(stderr, "Set speed to %d failed:%s\n", hz, strerror(errno)); return (-1); } if (ioctl_val != hz) { fprintf(stderr, "do not support speed %d,supported is %d\n", hz, ioctl_val); return (-1); } return (0); } /* * Usage():print help information * params:(none) * returns:(none) */ void Usage(void) { printf ("run: ./SndKit [-h] [-d device] [-c channel] [-b bits] [-f hz] [-l len] <-r|-p file>\n" "Description: implent raw sound record/play\n" "option:\n" "\t -h: print help informations\n" "\t -d device: assign sound device to record or playback(default /dev/dsp)\n" "\t -c channel: indicate in MONO or STEREO channel(default MONO)\n" "\t -b bits: assign sampling bits depth(default 8bits unsigned)\n" "\t -f hz: indicate sampling rate,i.e,frequence(default 8kbps)\n" "\t -l len: indicate recording sound's length(default 1024k)\n" "\t -r|-p file: indicate record in or playback(no default,must give out explicitly)\n" "e.g.:\n" "\t ./SndKit -h show help information\n" "\t ./SndKit -r record.wav record audio from microphone(/dev/dsp)\n" "\t ./SndKit -d /dev/dsp -p record.wav playback record.wav via /dev/dsp\n" "\t ./SndKit -b 8 -f 22 -r reacord.wav record audio in 8 bit & 22k hz\n" "\t ./SndKit -d /dev/dsp -c 2 -r record.wav record audio in /dev/dsp and stereo\n" "\t ./SndKit -r -l 40 record.wav record 40k audio data in record.wav\n"); }