Mixer group control structure
Synopsis:
typedef struct snd_mixer_group_s
{
snd_mixer_gid_t gid;
uint32_t caps;
uint32_t channels;
int32_t min, max;
union
{
uint32_t values[32];
struct
{
uint32_t front_left;
uint32_t front_right;
uint32_t front_center;
uint32_t rear_left;
uint32_t rear_right;
uint32_t woofer;
uint8_t reserved[128]; /* must be filled with zeroes */
} names;
} volume;
uint32_t mute;
uint32_t capture;
int32_t capture_group;
int32_t elements_size, elements, elements_over;
snd_mixer_eid_t *pelements;
uint16_t change_duration; /* milliseconds */
uint16_t spare;
int32_t min_dB, max_dB;
int32_t dB_scale_factor;
uint32_t balance_min;
uint32_t balance_max;
uint32_t balance_level;
uint32_t fade_level;
uint8_t reserved[99]; /* must be filled with zero */
} snd_mixer_group_t;
Description:
The snd_mixer_group_t
structure is the control structure for a mixer group. You can get the information for a
group by calling snd_mixer_group_read(), and set it by calling snd_mixer_group_write().
Some structure members are read-only and are ignored for
snd_mixer_group_write() calls. The change_duration
member is write-only and ignored for snd_mixer_group_read() calls.
The members of this structure include:
- gid
- A
snd_mixer_gid_t
structure that identifies the group.
This structure includes the group name and index.
- caps
- The capabilities of the group, expressed through any combination of these flags. Read only:
- SND_MIXER_GRPCAP_VOLUME — the group has at least one volume
control.
- SND_MIXER_GRPCAP_JOINTLY_VOLUME — all channel volume levels
for the group must be the same (ganged).
- SND_MIXER_GRPCAP_MUTE — the group has at least one mute
control.
- SND_MIXER_GRPCAP_JOINTLY_MUTE — all channel mute settings for
the group must be the same (ganged).
- SND_MIXER_GRPCAP_CAPTURE — the group can be captured
(recorded).
- SND_MIXER_GRPCAP_JOINTLY_CAPTURE — all channel capture
settings for the group must be the same (ganged).
- SND_MIXER_GRPCAP_EXCL_CAPTURE — only one group on this device
can be captured at a time.
- SND_MIXER_GRPCAP_BALANCE — group has balance controls.
- SND_MIXER_GRPCAP_FADE — group has fade controls.
- SND_MIXER_GRPCAP_PLAY_GRP — the group is a playback group.
- SND_MIXER_GRPCAP_CAP_GRP — the group is a capture group.
- SND_MIXER_GRPCAP_SUBCHANNEL — the group is a subchannel
control. It exists only while a PCM subchannel is allocated by an application.
- channels
- The mapped bits that correspond to the channels contained in this group. Read only.
For
example, for stereo right and left speakers, bits 1 and 2 (00011) are mapped; for the
center speaker, bit 3 (00100) is mapped.
- min, max
- The minimum and maximum values that define the volume range. Note that the minimum doesn't have
to be zero. Read only.
- volume
- A structure that contains the volume level for each channel in the group.
You can access the values accessed directly by name or indirectly through
the array of values.
Note:
If the group is jointly volumed, all volume values must be the
same; setting different values results in undefined behavior.
- mute
- The mute state of the group channels.
If the bit corresponding to the channel is set, the channel is muted.
Note:
If the group is jointly muted, all mute bits must be the same; setting the
bits differently results in undefined behavior.
- capture
- The capture state of the group channels.
If the bit corresponding to the channel is set, the channel is being
captured.
If the group is exclusively capture, setting capture on this group
means that another group is no longer being captured.
Note:
If the group is jointly captured, all capture bits must be the same;
setting the bits differently results in undefined behavior.
- capture_group
- Not currently used.
- elements_size
- The size of the memory block pointed to by pelements in units of
snd_mixer_eid_t. Read only.
- elements
- The number of element IDs that are currently valid in pelements. Read
only.
- elements_over
- The number of element IDs that were not returned in pelements because it
wasn't large enough. Read only.
- pelements
- A pointer to a region of memory (allocated by the calling
application) that's used to store an array of element IDs.
This is an array of
snd_mixer_eid_t
structures.
The elements that are returned are the component elements that make
up the group identified by gid.
- change_duration
- The number of milliseconds over which to ramp the volume. Write only.
- min_dB, max_dB
- The minimum and maximum sound levels, in decibels. Read only.
- dB_scale_factor
- The value by which min_dB and max_dB have been scaled.
Read only.
- balance_min
- The minimum balance. Read only. See Balance and
fade controls.
- balance_max
- The maximum balance. Read only.
- balance_level
- The balance level.
- fade_level
- The fade level.
Balance and fade controls
The balance and fade controls work like a slider where 0% corresponds to the left (balance) or
front (fade) channel and 100% to the right (balance) or rear (fade) channel. At 50%, the
balance or fade control applies no attenuation to any channels. A value less than 50% is
closer to left or front and attenuates right or rear, and a value greater than 50% is closer
to right or rear and attenuates left or front. For the center channel, moving the balance
away from 50% in either direction causes an attenuation. The woofer and low-frequency
effects (LFE) channels are treated like a rear channel — they are attenuated when you fade
towards the front.
The balance_min member corresponds to a 0% value for the range and
balance_max corresponds to a 100% value. For example, if
balance_min is 0 and balance_max is 200, a
balance_level of 100 balances the volume.
Classification:
QNX Neutrino