Manual Pages  — MIXER

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 SYNOPSIS DESCRIPTION Mixer Mixer device User-defined mixer controls Opening and closing the mixer Manipulating the mixer Defining and using mixer controls RETURN VALUES EXAMPLES Change the volume of a device Mute all unmuted devices Print all recording sources' names and volumes Loop through all mixer devices in the system SEE ALSO AUTHORS

Mixer library (libmixer, -lmixer)

#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);

The mixer library allows userspace programs to access and manipulate OSS sound mixers in a simple way.

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 example, 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 supported 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.

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 volumes in integers from 0-100, we normalize them to 32-bit floating point numbers. However, the volumes can be denormalized using the MIX_VOLDENORM macro if needed.
nctl
	Number of user-defined mixer controls associated with the device.
ctls
	A tail queue containing 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 example, if we have a volume control, the mod function will be responsible for handling volume changes.
print
	Function pointer to a control print function.

The application must first call the mixer_open() function to obtain a handle 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.

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 separate argument.

The mixer_remove_ctl() functions removes a control from the device its attached 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.

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 selected device on success and NULL on failure.

All functions set the value of errno on failure.

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);

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);

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 ,
                    dp->name, dp->vol.left, dp->vol.right);
}

(void)mixer_close(m);

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);
}

Christos Margiolis <Mt christos@FreeBSD.org>