lib/libmixer/mixer.3

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.Dd January 19, 2023
.Dt MIXER 3
.Os
.Sh NAME
.Nm mixer_open ,
.Nm mixer_close ,
.Nm mixer_get_dev ,
.Nm mixer_get_dev_byname ,
.Nm mixer_add_ctl ,
.Nm mixer_add_ctl_s ,
.Nm mixer_remove_ctl ,
.Nm mixer_get_ctl ,
.Nm mixer_get_ctl_byname ,
.Nm mixer_set_vol ,
.Nm mixer_set_mute ,
.Nm mixer_mod_recsrc ,
.Nm mixer_get_dunit ,
.Nm mixer_set_dunit ,
.Nm mixer_get_mode ,
.Nm mixer_get_nmixers ,
.Nm MIX_ISDEV ,
.Nm MIX_ISMUTE ,
.Nm MIX_ISREC ,
.Nm MIX_ISRECSRC ,
.Nm MIX_VOLNORM ,
.Nm MIX_VOLDENORM
.Nd interface to OSS mixers
.Sh LIBRARY
Mixer library (libmixer, -lmixer)
.Sh SYNOPSIS
.In mixer.h
.Ft struct mixer *
.Fn mixer_open "const char *name"
.Ft int
.Fn mixer_close "struct mixer *m"
.Ft struct mix_dev *
.Fn mixer_get_dev "struct mixer *m" "int devno"
.Ft struct mix_dev *
.Fn mixer_get_dev_byname "struct mixer *m" "name"
.Ft int
.Fn 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)"
.Ft int
.Fn mixer_add_ctl_s "mix_ctl_t *ctl"
.Ft int
.Fn mixer_remove_ctl "mix_ctl_t *ctl"
.Ft mix_ctl_t *
.Fn mixer_get_ctl "struct mix_dev *d" "int id"
.Ft mix_ctl_t *
.Fn mixer_get_ctl_byname "struct mix_dev *d" "const char *name"
.Ft int
.Fn mixer_set_vol "struct mixer *m" "mix_volume_t vol"
.Ft int
.Fn mixer_set_mute "struct mixer *m" "int opt"
.Ft int
.Fn mixer_mod_recsrc "struct mixer *m" "int opt"
.Ft int
.Fn mixer_get_dunit "void"
.Ft int
.Fn mixer_set_dunit "struct mixer *m" "int unit"
.Ft int
.Fn mixer_get_mode "int unit"
.Ft int
.Fn mixer_get_nmixers "void"
.Ft int
.Fn MIX_ISDEV "struct mixer *m" "int devno"
.Ft int
.Fn MIX_ISMUTE "struct mixer *m" "int devno"
.Ft int
.Fn MIX_ISREC "struct mixer *m" "int devno"
.Ft int
.Fn MIX_ISRECSRC "struct mixer *m" "int devno"
.Ft float
.Fn MIX_VOLNORM "int v"
.Ft int
.Fn MIX_VOLDENORM "float v"
.Sh DESCRIPTION
The
.Nm mixer
library allows userspace programs to access and manipulate OSS sound mixers in
a simple way.
.Ss Mixer
A mixer is described by the following structure:
.Bd -literal
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 */
};
.Ed
.Pp
The fields are follows:
.Bl -tag -width "f_default"
.It Fa devs
A tail queue structure containing all supported mixer devices.
.It Fa dev
A pointer to the currently selected device.
The device is one of the elements in
.Ar devs .
.It Fa mi
OSS information about the mixer.
Look at the definition of the
.Ft oss_mixerinfo
structure in
.In sys/soundcard.h
to see its fields.
.It Fa ci
OSS audio card information.
This structure is also defined in
.In sys/soundcard.h .
.It Fa name
Path to the mixer (e.g /dev/mixer0).
.It Fa fd
File descriptor returned when the mixer is opened in
.Fn mixer_open .
.It Fa unit
Audio card unit.
Since each mixer device maps to a pcmX device,
.Ar 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
.Ar unit
is 0 as well.
This number is useful when checking if the mixer's audio card is the default one.
.It Fa ndev
Number of devices in
.Ar devs .
.It Fa 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,
.Fn mixer_open
stores only the supported devices in devs, so it is very unlikely this mask will
be needed.
.It Fa mutemask
Bit mask containing all muted devices.
The logic is the same as with
.Ar devmask .
.It Fa recmask
Bit mask containing all recording devices.
Again, same logic as with the other masks.
.It Fa recsrc
Bit mask containing all recording sources.
Yes, same logic again.
.It Fa mode
Bit mask containing the supported modes for this audio device.
It holds the value of the
.Ar dev.pcm.X.mode
sysctl.
.It Fa f_default
Flag which tells whether the mixer's audio card is the default one.
.El
.Ss Mixer device
Each mixer device stored in a mixer is described as follows:
.Bd -literal
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;
};
.Ed
.Pp
The fields are follows:
.Bl -tag -width "parent_mixer"
.It Fa parent_mixer
Pointer to the mixer the device is attached to.
.It Fa name
Device name given by the OSS API.
Devices can have one of the following names:
.Bd -ragged
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.
.Ed
.It Fa devno
Device's index in the SOUND_MIXER_NRDEVICES macro defined in
.In sys/soundcard.h .
This number is used to check against the masks defined in the
.Ar mixer
structure.
.It Fa 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
.Ar MIX_VOLDENORM
macro if needed.
.It Fa nctl
Number of user-defined mixer controls associated with the device.
.It Fa ctls
A tail queue containing user-defined mixer controls.
.El
.Ss User-defined mixer controls
Each mixer device can have user-defined controls.
The control structure is defined as follows:
.Bd -literal
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;
};
.Ed
.Pp
The fields are follows:
.Bl -tag -width "parent_dev"
.It Fa parent_dev
Pointer to the device the control is attached to.
.It Fa 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.
.It Fa name
Control name.
As with
.Ar id ,
the caller has to make sure the same name is not used more than once.
.It Fa mod
Function pointer to a control modification function.
As in
.Xr mixer 8 ,
each mixer control's values can be modified.
For example, if we have a volume control, the
.Ar mod
function will be responsible for handling volume changes.
.It Fa print
Function pointer to a control print function.
.El
.Ss Opening and closing the mixer
The application must first call the
.Fn mixer_open
function to obtain a handle to the device, which is used as an argument \
in most other functions and macros.
The parameter
.Ar name
specifies the path to the mixer.
OSS mixers are stored under
.Ar /dev/mixerN
where
.Ar N
is the number of the mixer device.
Each device maps to an actual
.Ar pcm
audio card, so
.Ar /dev/mixer0
is the mixer for
.Ar pcm0 ,
and so on.
If
.Ar name
is
.Ar NULL
or
.Ar /dev/mixer ,
.Fn mixer_open
opens the default mixer (hw.snd.default_unit).
.Pp
The
.Fn 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.
.Ss Manipulating the mixer
The
.Fn mixer_get_dev
and
.Fn mixer_get_dev_byname
functions select a mixer device, either by its number or by its name respectively.
The mixer structure 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 functions has to be called.
.Pp
The
.Fn mixer_set_vol
function changes the volume of the selected mixer device.
The
.Ar vol
parameter is a structure that stores the left and right volumes of a given device.
The allowed volume values are between MIX_VOLMIN (0.0) and MIX_VOLMAX (1.0).
.Pp
The
.Fn mixer_set_mute
function modifies the mute of a selected device.
The
.Ar opt
parameter has to be one of the following options:
.Bl -tag -width MIX_TOGGLEMUTE -offset indent
.It Dv MIX_MUTE
Mute the device.
.It Dv MIX_UNMUTE
Unmute the device.
.It Dv MIX_TOGGLEMUTE
Toggle the device's mute (e.g mute if unmuted and unmute if muted).
.El
.Pp
The
.Fn mixer_mod_recsrc
function modifies a recording device.
The selected device has to be a recording device, otherwise the function will fail.
The
.Ar opt
parameter has to be one of the following options:
.Bl -tag -width MIX_REMOVERECSRC -offset indent
.It Dv MIX_ADDRECSRC
Add device to the recording sources.
.It Dv MIX_REMOVERECSRC
Remove device from the recording sources.
.It Dv MIX_SETRECSRC
Set device as the only recording source.
.It Dv MIX_TOGGLERECSRC
Toggle device from the recording sources.
.El
.Pp
The
.Fn mixer_get_dunit
and
.Fn mixer_set_dunit
functions get and set the default audio card in the system.
Although this is not really a mixer feature, it is useful to have instead of \
having to use the
.Xr sysctl 3
controls.
.Pp
The
.Fn mixer_get_mode
function returns the playback/recording mode of the audio device the mixer \
belongs to.
The available values are the following:
.Bl -tag -width "MIX_STATUS_PLAY | MIX_STATUS_REC" -offset indent
.It Dv MIX_STATUS_NONE
Neither playback nor recording.
.It Dv MIX_STATUS_PLAY
Playback.
.It Dv MIX_STATUS_REC
Recording.
.It Dv MIX_STATUS_PLAY | MIX_STATUS_REC
Playback and recording.
.El
.Pp
The
.Fn mixer_get_nmixers
function returns the total number of mixer devices in the system.
.Pp
The
.Fn 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.
.Pp
The
.Fn MIX_ISMUTE
macro checks if a device is muted.
.Pp
The
.Fn MIX_ISREC
macro checks if a device is a recording device.
.Pp
The
.Fn MIX_ISRECSRC
macro checks if a device is a recording source.
.Pp
The
.Fn MIX_VOLNORM
macro normalizes a value to 32-bit floating point number.
It is used to normalize the volumes read from the OSS API.
.Pp
The
.Fn MIX_VOLDENORM
macro denormalizes the left and right volumes stores in the
.Ft mix_dev
structure.
.Ss Defining and using mixer controls
The
.Fn mix_add_ctl
function creates a control and attaches it to the device specified in the
.Ar parent
argument.
.Pp
The
.Fn mix_add_ctl_s
function does the same thing as with
.Fn mix_add_ctl
but the caller passes a
.Ft mix_ctl_t *
structure instead of each field as a separate argument.
.Pp
The
.Fn mixer_remove_ctl
functions removes a control from the device its attached to.
.Pp
The
.Fn mixer_get_ctl
function searches for a control in the device specified in the
.Ar d
argument and returns a pointer to it.
The search is done using the control's ID.
.Pp
The
.Fn mixer_get_ctl_byname
function is the same as with
.Fn mixer_get_ctl
but the search is done using the control's name.
.Sh RETURN VALUES
The
.Fn mixer_open
function returns the newly created handle on success and NULL on failure.
.Pp
The
.Fn mixer_close ,
.Fn mixer_set_vol ,
.Fn mixer_set_mute ,
.Fn mixer_mod_recsrc ,
.Fn mixer_get_dunut ,
.Fn mixer_set_dunit
and
.Fn mixer_get_nmixers
functions return 0 or positive values on success and -1 on failure.
.Pp
The
.Fn mixer_get_dev
and
.Fn mixer_get_dev_byname
functions return the selected device on success and NULL on failure.
.Pp
All functions set the value of
.Ar errno
on failure.
.Sh EXAMPLES
.Ss Change the volume of a device
.Bd -literal
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);
.Ed
.Ss Mute all unmuted devices
.Bd -literal
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);
.Ed
.Ss Print all recording sources' names and volumes
.Bd -literal
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);
.Ed
.Sh SEE ALSO
.Xr queue 3 ,
.Xr sysctl 3 ,
.Xr sound 4 ,
.Xr mixer 8
and
.Xr errno 2
.Sh AUTHORS
.An Christos Margiolis Aq Mt christos@FreeBSD.org