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MIXER(3) Library Functions Manual MIXER(3) NAME mixer_open, mixer_close, mixer_get_dev, mixer_get_dev_byname, mixer_add_ctl, mixer_add_ctl_s, mixer_remove_ctl, mixer_get_ctl, mixer_get_ctl_byname, mixer_set_vol, mixer_set_mute, mixer_mod_recsrc, mixer_get_dunit, mixer_set_dunit, mixer_get_mode, mixer_get_nmixers, mixer_get_path, MIX_ISDEV, MIX_ISMUTE, MIX_ISREC, MIX_ISRECSRC, MIX_VOLNORM, MIX_VOLDENORM -- interface to OSS mixers LIBRARY Mixer library (libmixer, -lmixer) SYNOPSIS #include <mixer.h> struct mixer * mixer_open(const char *name); int mixer_close(struct mixer *m); struct mix_dev * mixer_get_dev(struct mixer *m, int devno); struct mix_dev * mixer_get_dev_byname(struct mixer *m, name); int mixer_add_ctl(struct mix_dev *parent, int id, const char *name, int (*mod)(struct mix_dev *d, void *p), int (*print)(struct mix_dev *d, void *p)); int mixer_add_ctl_s(mix_ctl_t *ctl); int mixer_remove_ctl(mix_ctl_t *ctl); mix_ctl_t * mixer_get_ctl(struct mix_dev *d, int id); mix_ctl_t * mixer_get_ctl_byname(struct mix_dev *d, const char *name); int mixer_set_vol(struct mixer *m, mix_volume_t vol); int mixer_set_mute(struct mixer *m, int opt); int mixer_mod_recsrc(struct mixer *m, int opt); int mixer_get_dunit(void); int mixer_set_dunit(struct mixer *m, int unit); int mixer_get_mode(int unit); int mixer_get_nmixers(void); int mixer_get_path(char * buf, size_t size, int unit); int MIX_ISDEV(struct mixer *m, int devno); int MIX_ISMUTE(struct mixer *m, int devno); int MIX_ISREC(struct mixer *m, int devno); int MIX_ISRECSRC(struct mixer *m, int devno); float MIX_VOLNORM(int v); int MIX_VOLDENORM(float v); DESCRIPTION The mixer library allows userspace programs to access and manipulate OSS sound mixers in a simple way. Mixer A mixer is described by the following structure: struct mixer { TAILQ_HEAD(mix_devhead, mix_dev) devs; /* device list */ struct mix_dev *dev; /* selected device */ oss_mixerinfo mi; /* mixer info */ oss_card_info ci; /* audio card info */ char name[NAME_MAX]; /* mixer name (e.g /dev/mixer0) */ int fd; /* file descriptor */ int unit; /* audio card unit */ int ndev; /* number of devices */ int devmask; /* supported devices */ #define MIX_MUTE 0x01 #define MIX_UNMUTE 0x02 #define MIX_TOGGLEMUTE 0x04 int mutemask; /* muted devices */ int recmask; /* recording devices */ #define MIX_ADDRECSRC 0x01 #define MIX_REMOVERECSRC 0x02 #define MIX_SETRECSRC 0x04 #define MIX_TOGGLERECSRC 0x08 int recsrc; /* recording sources */ #define MIX_MODE_MIXER 0x01 #define MIX_MODE_PLAY 0x02 #define MIX_MODE_REC 0x04 int mode; /* dev.pcm.X.mode sysctl */ int f_default; /* default mixer flag */ }; The fields are follows: devs A tail queue structure containing all supported mixer devices. dev A pointer to the currently selected device. The device is one of the elements in devs. mi OSS information about the mixer. Look at the definition of the oss_mixerinfo structure in <sys/soundcard.h> to see its fields. ci OSS audio card information. This structure is also defined in <sys/soundcard.h>. name Path to the mixer (e.g /dev/mixer0). fd File descriptor returned when the mixer is opened in mixer_open(). unit Audio card unit. Since each mixer device maps to a pcmX device, unit is always equal to the number of that pcmX device. For ex- ample, if the audio device's number is 0 (i.e pcm0), then unit is 0 as well. This number is useful when checking if the mixer's audio card is the default one. ndev Number of devices in devs. devmask Bit mask containing all supported devices for the mixer. For example, if device 10 is supported, then the 10th bit in the mask will be set. By default, mixer_open() stores only the sup- ported devices in devs, so it is very unlikely this mask will be needed. mutemask Bit mask containing all muted devices. The logic is the same as with devmask. recmask Bit mask containing all recording devices. Again, same logic as with the other masks. recsrc Bit mask containing all recording sources. Yes, same logic again. mode Bit mask containing the supported modes for this audio device. It holds the value of the dev.pcm.X.mode sysctl. f_default Flag which tells whether the mixer's audio card is the default one. Mixer device Each mixer device stored in a mixer is described as follows: struct mix_dev { struct mixer *parent_mixer; /* parent mixer */ char name[NAME_MAX]; /* device name (e.g "vol") */ int devno; /* device number */ struct mix_volume { #define MIX_VOLMIN 0.0f #define MIX_VOLMAX 1.0f #define MIX_VOLNORM(v) ((v) / 100.0f) #define MIX_VOLDENORM(v) ((int)((v) * 100.0f + 0.5f)) float left; /* left volume */ float right; /* right volume */ } vol; int nctl; /* number of controls */ TAILQ_HEAD(mix_ctlhead, mix_ctl) ctls; /* control list */ TAILQ_ENTRY(mix_dev) devs; }; The fields are follows: parent_mixer Pointer to the mixer the device is attached to. name Device name given by the OSS API. Devices can have one of the following names: vol, bass, treble, synth, pcm, speaker, line, mic, cd, mix, pcm2, rec, igain, ogain, line1, line2, line3, dig1, dig2, dig3, phin, phout, video, radio, and monitor. devno Device's index in the SOUND_MIXER_NRDEVICES macro defined in <sys/soundcard.h>. This number is used to check against the masks defined in the mixer structure. left right Left and right-ear volumes. Although the OSS API stores vol- umes in integers from 0-100, we normalize them to 32-bit floating point numbers. However, the volumes can be denor- malized using the MIX_VOLDENORM macro if needed. nctl Number of user-defined mixer controls associated with the de- vice. ctls A tail queue containing user-defined mixer controls. User-defined mixer controls Each mixer device can have user-defined controls. The control structure is defined as follows: struct mix_ctl { struct mix_dev *parent_dev; /* parent device */ int id; /* control id */ char name[NAME_MAX]; /* control name */ int (*mod)(struct mix_dev *, void *); /* modify control values */ int (*print)(struct mix_dev *, void *); /* print control */ TAILQ_ENTRY(mix_ctl) ctls; }; The fields are follows: parent_dev Pointer to the device the control is attached to. id Control ID assigned by the caller. Even though the library will report it, care has to be taken to not give a control the same ID in case the caller has to choose controls using their ID. name Control name. As with id, the caller has to make sure the same name is not used more than once. mod Function pointer to a control modification function. As in mixer(8), each mixer control's values can be modified. For ex- ample, if we have a volume control, the mod function will be responsible for handling volume changes. print Function pointer to a control print function. Opening and closing the mixer The application must first call the mixer_open() function to obtain a han- dle to the device, which is used as an argument in most other functions and macros. The parameter name specifies the path to the mixer. OSS mixers are stored under /dev/mixerN where N is the number of the mixer device. Each device maps to an actual pcm audio card, so /dev/mixer0 is the mixer for pcm0, and so on. If name is NULL or /dev/mixer, mixer_open() opens the default mixer (hw.snd.default_unit). The mixer_close() function frees resources and closes the mixer device. It is a good practice to always call it when the application is done using the mixer. Manipulating the mixer The mixer_get_dev() and mixer_get_dev_byname() functions select a mixer de- vice, either by its number or by its name respectively. The mixer struc- ture keeps a list of all the devices, but only one can be manipulated at a time. Each time a new device is to be manipulated, one of the two func- tions has to be called. The mixer_set_vol() function changes the volume of the selected mixer de- vice. The vol parameter is a structure that stores the left and right vol- umes of a given device. The allowed volume values are between MIX_VOLMIN (0.0) and MIX_VOLMAX (1.0). The mixer_set_mute() function modifies the mute of a selected device. The opt parameter has to be one of the following options: MIX_MUTE Mute the device. MIX_UNMUTE Unmute the device. MIX_TOGGLEMUTE Toggle the device's mute (e.g mute if unmuted and un- mute if muted). The mixer_mod_recsrc() function modifies a recording device. The selected device has to be a recording device, otherwise the function will fail. The opt parameter has to be one of the following options: MIX_ADDRECSRC Add device to the recording sources. MIX_REMOVERECSRC Remove device from the recording sources. MIX_SETRECSRC Set device as the only recording source. MIX_TOGGLERECSRC Toggle device from the recording sources. The mixer_get_dunit() and mixer_set_dunit() functions get and set the de- fault audio card in the system. Although this is not really a mixer fea- ture, it is useful to have instead of having to use the sysctl(3) controls. The mixer_get_mode() function returns the operating mode of the audio de- vice the mixer belongs to. The following values can be OR'ed in case more than one mode is supported: MIX_MODE_MIXER The audio device has a mixer. MIX_MODE_PLAY The audio device supports playback. MIX_MODE_REC The audio device supports recording. The mixer_get_nmixers() function returns the maximum mixer unit number. Although this might sound as incorrect behavior, given that one would ex- pect "nmixers" to refer to the total number of active mixers, it is more intuitive for applications that want to loop through all mixer devices (see the "EXAMPLES" section). The mixer_get_path() function writes the path of the mixer device specified in the unit argument to the buffer specified in buf. unit can be either -1, in which case mixer_get_path() will fetch the path of the default mixer, or between 0 and the maximum mixer unit. The MIX_ISDEV() macro checks if a device is actually a valid device for a given mixer. It is very unlikely that this macro will ever be needed since the library stores only valid devices by default. The MIX_ISMUTE() macro checks if a device is muted. The MIX_ISREC() macro checks if a device is a recording device. The MIX_ISRECSRC() macro checks if a device is a recording source. The MIX_VOLNORM() macro normalizes a value to 32-bit floating point number. It is used to normalize the volumes read from the OSS API. The MIX_VOLDENORM() macro denormalizes the left and right volumes stores in the mix_dev structure. Defining and using mixer controls The mix_add_ctl() function creates a control and attaches it to the device specified in the parent argument. The mix_add_ctl_s() function does the same thing as with mix_add_ctl() but the caller passes a mix_ctl_t * structure instead of each field as a sepa- rate argument. The mixer_remove_ctl() functions removes a control from the device its at- tached to. The mixer_get_ctl() function searches for a control in the device specified in the d argument and returns a pointer to it. The search is done using the control's ID. The mixer_get_ctl_byname() function is the same as with mixer_get_ctl() but the search is done using the control's name. RETURN VALUES The mixer_open() function returns the newly created handle on success and NULL on failure. The mixer_close(), mixer_set_vol(), mixer_set_mute(), mixer_mod_recsrc(), mixer_get_dunut(), mixer_set_dunit(), mixer_get_nmixers(), and mixer_get_path() functions return 0 or positive values on success and -1 on failure. The mixer_get_dev() and mixer_get_dev_byname() functions return the se- lected device on success and NULL on failure. All functions set the value of errno on failure. EXAMPLES Change the volume of a device struct mixer *m; mix_volume_t vol; char *mix_name, *dev_name; mix_name = ...; if ((m = mixer_open(mix_name)) == NULL) err(1, "mixer_open: %s", mix_name); dev_name = ...; if ((m->dev = mixer_get_dev_byname(m, dev_name)) < 0) err(1, "unknown device: %s", dev_name); vol.left = ...; vol.right = ....; if (mixer_set_vol(m, vol) < 0) warn("cannot change volume"); (void)mixer_close(m); Mute all unmuted devices struct mixer *m; struct mix_dev *dp; if ((m = mixer_open(NULL)) == NULL) /* Open the default mixer. */ err(1, "mixer_open"); TAILQ_FOREACH(dp, &m->devs, devs) { m->dev = dp; /* Select device. */ if (M_ISMUTE(m, dp->devno)) continue; if (mixer_set_mute(m, MIX_MUTE) < 0) warn("cannot mute device: %s", dp->name); } (void)mixer_close(m); Print all recording sources' names and volumes struct mixer *m; struct mix_dev *dp; char *mix_name, *dev_name; mix_name = ...; if ((m = mixer_open(mix_name)) == NULL) err(1, "mixer_open: %s", mix_name); TAILQ_FOREACH(dp, &m->devs, devs) { if (M_ISRECSRC(m, dp->devno)) printf("%s\t%.2f:%.2f\n", dp->name, dp->vol.left, dp->vol.right); } (void)mixer_close(m); Loop through all mixer devices in the system struct mixer *m; char buf[NAME_MAX]; int n; if ((n = mixer_get_nmixers()) < 0) errx(1, "no mixers present in the system"); for (i = 0; i < n; i++) { (void)mixer_get_path(buf, sizeof(buf), i); if ((m = mixer_open(buf)) == NULL) continue; ... (void)mixer_close(m); } SEE ALSO queue(3), sysctl(3), sound(4), mixer(8) and errno(2) AUTHORS Christos Margiolis <christos@FreeBSD.org> FreeBSD ports 15.quarterly August 4, 2024 MIXER(3)
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUES | EXAMPLES | SEE ALSO | AUTHORS
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