#define SND_CHMAP_API_VERSION ((1 << 16) | (0 << 8) | 1) |
channel mapping API version number
#define SND_CHMAP_DRIVER_SPEC (0x02 << 16) |
bit flag indicating the non-standard channel value
#define SND_CHMAP_PHASE_INVERSE (0x01 << 16) |
bit flag indicating the channel is phase inverted
#define SND_CHMAP_POSITION_MASK 0xffff |
bitmask for channel position
#define SND_PCM_ABORT 0x00008000 |
In an abort state (internal, not allowed for open)
#define SND_PCM_ASYNC |
Async notification (flag for open mode)
#define SND_PCM_DLSYM_VERSION _dlsym_pcm_001 |
dlsym version for interface entry callback
#define SND_PCM_NO_AUTO_CHANNELS 0x00020000 |
Disable automatic (but not forced!) channel conversion
#define SND_PCM_NO_AUTO_FORMAT 0x00040000 |
Disable automatic (but not forced!) format conversion
#define SND_PCM_NO_AUTO_RESAMPLE 0x00010000 |
Disable automatic (but not forced!) rate resamplinig
#define SND_PCM_NO_SOFTVOL 0x00080000 |
Disable soft volume control
#define SND_PCM_NONBLOCK |
Non blocking mode (flag for open mode)
typedef struct _snd_pcm_access_mask snd_pcm_access_mask_t |
PCM access types mask
typedef struct _snd_pcm_format_mask snd_pcm_format_mask_t |
PCM formats mask
typedef struct _snd_pcm_hw_params snd_pcm_hw_params_t |
PCM hardware configuration space container
snd_pcm_hw_params_t is an opaque structure which contains a set of possible PCM hardware configurations. For example, a given instance might include a range of buffer sizes, a range of period sizes, and a set of several sample formats. Some subset of all possible combinations these sets may be valid, but not necessarily any combination will be valid.
When a parameter is set or restricted using a snd_pcm_hw_params_set* function, all of the other ranges will be updated to exclude as many impossible configurations as possible. Attempting to set a parameter outside of its acceptable range will result in the function failing and an error code being returned.
typedef struct _snd_pcm_info snd_pcm_info_t |
PCM generic info container
typedef struct _snd_pcm_scope snd_pcm_scope_t |
SND_PCM_TYPE_METER scope handle
typedef long snd_pcm_sframes_t |
Signed frames quantity
typedef struct _snd_pcm_status snd_pcm_status_t |
PCM status container
typedef struct _snd_pcm_subformat_mask snd_pcm_subformat_mask_t |
PCM subformats mask
typedef struct _snd_pcm_sw_params snd_pcm_sw_params_t |
PCM software configuration container
typedef struct _snd_pcm snd_pcm_t |
PCM handle
typedef enum _snd_pcm_type snd_pcm_type_t |
PCM type
typedef unsigned long snd_pcm_uframes_t |
Unsigned frames quantity
enum _snd_pcm_type |
PCM type
enum snd_pcm_access_t |
PCM access type
channel positions
enum snd_pcm_chmap_type |
enum snd_pcm_class_t |
enum snd_pcm_format_t |
PCM sample format
enum snd_pcm_start_t |
enum snd_pcm_state_t |
PCM state
enum snd_pcm_stream_t |
enum snd_pcm_subclass_t |
enum snd_pcm_subformat_t |
enum snd_pcm_tstamp_t |
PCM timestamp mode
SND_PCM_TSTAMP_NONE | No timestamp |
SND_PCM_TSTAMP_ENABLE | Update timestamp at every hardware position update |
SND_PCM_TSTAMP_MMAP | Equivalent with SND_PCM_TSTAMP_ENABLE, just for compatibility with older versions |
enum snd_pcm_xrun_t |
int snd_async_add_pcm_handler | ( | snd_async_handler_t ** | handler, | |
snd_pcm_t * | pcm, | |||
snd_async_callback_t | callback, | |||
void * | private_data | |||
) |
Add an async handler for a PCM.
handler | Returned handler handle | |
pcm | PCM handle | |
callback | Callback function | |
private_data | Callback private data |
snd_pcm_t* snd_async_handler_get_pcm | ( | snd_async_handler_t * | handler | ) |
Return PCM handle related to an async handler.
handler | Async handler handle |
snd_pcm_sframes_t snd_pcm_avail | ( | snd_pcm_t * | pcm | ) |
Return number of frames ready to be read (capture) / written (playback).
pcm | PCM handle |
The position is synced with hardware (driver) position in the sound ring buffer in this functions.
The function is thread-safe when built with the proper option.
int snd_pcm_avail_delay | ( | snd_pcm_t * | pcm, | |
snd_pcm_sframes_t * | availp, | |||
snd_pcm_sframes_t * | delayp | |||
) |
Combine snd_pcm_avail and snd_pcm_delay functions.
pcm | PCM handle | |
availp | Number of available frames in the ring buffer | |
delayp | Total I/O latency in frames |
The function is thread-safe when built with the proper option.
snd_pcm_sframes_t snd_pcm_avail_update | ( | snd_pcm_t * | pcm | ) |
Return number of frames ready to be read (capture) / written (playback).
pcm | PCM handle |
The position is not synced with hardware (driver) position in the sound ring buffer in this function. This function is a light version of snd_pcm_avail() .
Using this function is ideal after poll() or select() when audio file descriptor made the event and when application expects just period timing.
Also this function might be called after snd_pcm_delay() or snd_pcm_hwsync() functions to move private ring buffer pointers in alsa-lib (the internal plugin chain).
The function is thread-safe when built with the proper option.
unsigned int snd_pcm_chmap_from_string | ( | const char * | str | ) |
\!brief Convert from string to channel position
str | The string to parse |
const char* snd_pcm_chmap_long_name | ( | enum snd_pcm_chmap_position | val | ) |
\!brief Get a longer name string for a standard channel map position
val | Channel position |
const char* snd_pcm_chmap_name | ( | enum snd_pcm_chmap_position | val | ) |
\!brief Get a name string for a standard channel map position
val | Channel position |
snd_pcm_chmap_t* snd_pcm_chmap_parse_string | ( | const char * | str | ) |
\!brief Convert from string to channel map
str | The string to parse |
int snd_pcm_chmap_print | ( | const snd_pcm_chmap_t * | map, | |
size_t | maxlen, | |||
char * | buf | |||
) |
\!brief Print the channels in chmap on the buffer
map | The channel map to print | |
maxlen | The maximal length to write (including NUL letter) | |
buf | The buffer to write |
const char* snd_pcm_chmap_type_name | ( | enum snd_pcm_chmap_type | val | ) |
\!brief Get a name string for a channel map type as query results
val | Channel position |
int snd_pcm_close | ( | snd_pcm_t * | pcm | ) |
close PCM handle
pcm | PCM handle |
int snd_pcm_delay | ( | snd_pcm_t * | pcm, | |
snd_pcm_sframes_t * | delayp | |||
) |
Obtain delay for a running PCM handle.
pcm | PCM handle | |
delayp | Returned delay in frames |
For capture the delay is defined as the time that a frame that was digitized by the audio device takes until it can be read from the PCM stream shortly after this call returns. It is as such the overall latency from the initial ADC to the read call.
Please note that hence in case of a playback underrun this value will not necessarily got down to 0.
If the application is interested in the fill level of the playback buffer of the device, it should use snd_pcm_avail*() functions. The value returned by that call is not directly related to the delay, since the latter might include some additional, fixed latencies the former does not.
Note this function does not update the actual r/w pointer for applications. The function snd_pcm_avail_update() have to be called before any begin+commit operation.
The function is thread-safe when built with the proper option.
int snd_pcm_drain | ( | snd_pcm_t * | pcm | ) |
Stop a PCM preserving pending frames.
pcm | PCM handle |
-ESTRPIPE | a suspend event occurred |
For stopping the PCM stream immediately, use ::snd_pcm_drop() instead.
The function is thread-safe when built with the proper option.
int snd_pcm_drop | ( | snd_pcm_t * | pcm | ) |
Stop a PCM dropping pending frames.
pcm | PCM handle |
For processing all pending samples, use ::snd_pcm_drain() instead.
The function is thread-safe when built with the proper option.
snd_pcm_sframes_t snd_pcm_forward | ( | snd_pcm_t * | pcm, | |
snd_pcm_uframes_t | frames | |||
) |
Move application frame position forward.
pcm | PCM handle | |
frames | wanted skip in frames |
0 | means no action |
snd_pcm_sframes_t snd_pcm_forwardable | ( | snd_pcm_t * | pcm | ) |
Get safe count of frames which can be forwarded.
pcm | PCM handle |
The function is thread-safe when built with the proper option.
void snd_pcm_free_chmaps | ( | snd_pcm_chmap_query_t ** | maps | ) |
\!brief Release the channel map array allocated via snd_pcm_query_chmaps
maps | the array pointer to release |
snd_pcm_chmap_t* snd_pcm_get_chmap | ( | snd_pcm_t * | pcm | ) |
\!brief Get the current channel map
pcm | PCM instance |
int snd_pcm_get_params | ( | snd_pcm_t * | pcm, | |
snd_pcm_uframes_t * | buffer_size, | |||
snd_pcm_uframes_t * | period_size | |||
) |
Get the transfer size parameters in a simple way.
pcm | PCM handle | |
buffer_size | PCM ring buffer size in frames | |
period_size | PCM period size in frames |
int snd_pcm_htimestamp | ( | snd_pcm_t * | pcm, | |
snd_pcm_uframes_t * | avail, | |||
snd_htimestamp_t * | tstamp | |||
) |
Obtain last position update hi-res timestamp.
pcm | PCM handle | |
avail | Number of available frames when timestamp was grabbed | |
tstamp | Hi-res timestamp |
The function is thread-safe when built with the proper option.
int snd_pcm_hw_free | ( | snd_pcm_t * | pcm | ) |
Remove PCM hardware configuration and free associated resources.
pcm | PCM handle |
int snd_pcm_hw_params | ( | snd_pcm_t * | pcm, | |
snd_pcm_hw_params_t * | params | |||
) |
Install one PCM hardware configuration chosen from a configuration space and snd_pcm_prepare it.
pcm | PCM handle | |
params | Configuration space definition container |
After this call, snd_pcm_prepare() is called automatically and the stream is brought to SND_PCM_STATE_PREPARED
state.
The hardware parameters cannot be changed when the stream is running (active). The software parameters can be changed at any time.
The configuration space will be updated to reflect the chosen parameters.
int snd_pcm_hw_params_current | ( | snd_pcm_t * | pcm, | |
snd_pcm_hw_params_t * | params | |||
) |
Retreive current PCM hardware configuration chosen with snd_pcm_hw_params.
pcm | PCM handle | |
params | Configuration space definition container |
int snd_pcm_hwsync | ( | snd_pcm_t * | pcm | ) |
(DEPRECATED) Synchronize stream position with hardware
pcm | PCM handle |
The function is thread-safe when built with the proper option.
int snd_pcm_info | ( | snd_pcm_t * | pcm, | |
snd_pcm_info_t * | info | |||
) |
Obtain general (static) information for PCM handle.
pcm | PCM handle | |
info | Information container |
Link two PCMs.
pcm1 | first PCM handle | |
pcm2 | first PCM handle |
const char* snd_pcm_name | ( | snd_pcm_t * | pcm | ) |
get identifier of PCM handle
pcm | PCM handle |
int snd_pcm_nonblock | ( | snd_pcm_t * | pcm, | |
int | nonblock | |||
) |
set nonblock mode
pcm | PCM handle | |
nonblock | 0 = block, 1 = nonblock mode, 2 = abort |
int snd_pcm_open | ( | snd_pcm_t ** | pcmp, | |
const char * | name, | |||
snd_pcm_stream_t | stream, | |||
int | mode | |||
) |
Opens a PCM.
pcmp | Returned PCM handle | |
name | ASCII identifier of the PCM handle | |
stream | Wanted stream | |
mode | Open mode (see SND_PCM_NONBLOCK, SND_PCM_ASYNC) |
int snd_pcm_open_fallback | ( | snd_pcm_t ** | pcmp, | |
snd_config_t * | root, | |||
const char * | name, | |||
const char * | orig_name, | |||
snd_pcm_stream_t | stream, | |||
int | mode | |||
) |
Opens a fallback PCM.
pcmp | Returned PCM handle | |
root | Configuration root | |
name | ASCII identifier of the PCM handle | |
orig_name | The original ASCII name | |
stream | Wanted stream | |
mode | Open mode (see SND_PCM_NONBLOCK, SND_PCM_ASYNC) |
int snd_pcm_open_lconf | ( | snd_pcm_t ** | pcmp, | |
const char * | name, | |||
snd_pcm_stream_t | stream, | |||
int | mode, | |||
snd_config_t * | lconf | |||
) |
Opens a PCM using local configuration.
pcmp | Returned PCM handle | |
name | ASCII identifier of the PCM handle | |
stream | Wanted stream | |
mode | Open mode (see SND_PCM_NONBLOCK, SND_PCM_ASYNC) | |
lconf | Local configuration |
int snd_pcm_pause | ( | snd_pcm_t * | pcm, | |
int | enable | |||
) |
Pause/resume PCM.
pcm | PCM handle | |
enable | 0 = resume, 1 = pause |
The function is thread-safe when built with the proper option.
int snd_pcm_poll_descriptors | ( | snd_pcm_t * | pcm, | |
struct pollfd * | pfds, | |||
unsigned int | space | |||
) |
get poll descriptors
pcm | PCM handle | |
pfds | array of poll descriptors | |
space | space in the poll descriptor array |
The result is intended for direct use with the poll() syscall.
For reading the returned events of poll descriptor after poll() system call, use ::snd_pcm_poll_descriptors_revents() function. The field values in pollfd structs may be bogus regarding the stream direction from the application perspective (POLLIN might not imply read direction and POLLOUT might not imply write), but the ::snd_pcm_poll_descriptors_revents() function does the right "demangling".
You can use output from this function as arguments for the select() syscall, too. Do not forget to translate POLLIN and POLLOUT events to corresponding FD_SET arrays and demangle events using ::snd_pcm_poll_descriptors_revents() .
The function is thread-safe when built with the proper option.
int snd_pcm_poll_descriptors_count | ( | snd_pcm_t * | pcm | ) |
get count of poll descriptors for PCM handle
pcm | PCM handle |
int snd_pcm_poll_descriptors_revents | ( | snd_pcm_t * | pcm, | |
struct pollfd * | pfds, | |||
unsigned int | nfds, | |||
unsigned short * | revents | |||
) |
get returned events from poll descriptors
pcm | PCM handle | |
pfds | array of poll descriptors | |
nfds | count of poll descriptors | |
revents | pointer to the returned (single) event |
Note: The null event also exists. Even if poll() or select() syscall returned that some events are waiting, this function might return empty set of events. In this case, application should do next event waiting using poll() or select().
Note: Even if multiple poll descriptors are used (i.e. pfds > 1), this function returns only a single event.
The function is thread-safe when built with the proper option.
int snd_pcm_prepare | ( | snd_pcm_t * | pcm | ) |
Prepare PCM for use.
pcm | PCM handle |
snd_pcm_chmap_query_t** snd_pcm_query_chmaps | ( | snd_pcm_t * | pcm | ) |
\!brief Query the available channel maps
pcm | PCM handle to query |
snd_pcm_chmap_query_t** snd_pcm_query_chmaps_from_hw | ( | int | card, | |
int | dev, | |||
int | subdev, | |||
snd_pcm_stream_t | stream | |||
) |
\!brief Query the available channel maps
card | the card number | |
dev | the PCM device number | |
subdev | the PCM substream index | |
stream | the direction of PCM stream |
As the parameters stand, the query is performed only to the hw PCM devices, not the abstracted PCM object in alsa-lib.
snd_pcm_sframes_t snd_pcm_readi | ( | snd_pcm_t * | pcm, | |
void * | buffer, | |||
snd_pcm_uframes_t | size | |||
) |
Read interleaved frames from a PCM.
pcm | PCM handle | |
buffer | frames containing buffer | |
size | frames to be read |
-EBADFD | PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING) | |
-EPIPE | an overrun occurred | |
-ESTRPIPE | a suspend event occurred (stream is suspended and waiting for an application recovery) |
If the non-blocking behaviour is selected, then routine doesn't wait at all.
The function is thread-safe when built with the proper option.
snd_pcm_sframes_t snd_pcm_readn | ( | snd_pcm_t * | pcm, | |
void ** | bufs, | |||
snd_pcm_uframes_t | size | |||
) |
Read non interleaved frames to a PCM.
pcm | PCM handle | |
bufs | frames containing buffers (one for each channel) | |
size | frames to be read |
-EBADFD | PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING) | |
-EPIPE | an overrun occurred | |
-ESTRPIPE | a suspend event occurred (stream is suspended and waiting for an application recovery) |
If the non-blocking behaviour is selected, then routine doesn't wait at all.
The function is thread-safe when built with the proper option.
int snd_pcm_recover | ( | snd_pcm_t * | pcm, | |
int | err, | |||
int | silent | |||
) |
Recover the stream state from an error or suspend.
pcm | PCM handle | |
err | error number | |
silent | do not print error reason |
This functions handles -EINTR (interrupted system call), -EPIPE (overrun or underrun) and -ESTRPIPE (stream is suspended) error codes trying to prepare given stream for next I/O.
Note that this function returs the original error code when it is not handled inside this function (for example -EAGAIN is returned back).
int snd_pcm_reset | ( | snd_pcm_t * | pcm | ) |
Reset PCM position.
pcm | PCM handle |
The function is thread-safe when built with the proper option.
int snd_pcm_resume | ( | snd_pcm_t * | pcm | ) |
Resume from suspend, no samples are lost.
pcm | PCM handle |
-EAGAIN | resume can't be proceed immediately (audio hardware is probably still suspended) | |
-ENOSYS | hardware doesn't support this feature |
The function is thread-safe when built with the proper option.
snd_pcm_sframes_t snd_pcm_rewind | ( | snd_pcm_t * | pcm, | |
snd_pcm_uframes_t | frames | |||
) |
Move application frame position backward.
pcm | PCM handle | |
frames | wanted displacement in frames |
snd_pcm_sframes_t snd_pcm_rewindable | ( | snd_pcm_t * | pcm | ) |
Get safe count of frames which can be rewinded.
pcm | PCM handle |
The function is thread-safe when built with the proper option.
int snd_pcm_set_chmap | ( | snd_pcm_t * | pcm, | |
const snd_pcm_chmap_t * | map | |||
) |
\!brief Configure the current channel map
pcm | PCM instance | |
map | the channel map to write |
int snd_pcm_set_params | ( | snd_pcm_t * | pcm, | |
snd_pcm_format_t | format, | |||
snd_pcm_access_t | access, | |||
unsigned int | channels, | |||
unsigned int | rate, | |||
int | soft_resample, | |||
unsigned int | latency | |||
) |
Set the hardware and software parameters in a simple way.
pcm | PCM handle | |
format | required PCM format | |
access | required PCM access | |
channels | required PCM channels | |
rate | required sample rate in Hz | |
soft_resample | 0 = disallow alsa-lib resample stream, 1 = allow resampling | |
latency | required overall latency in us |
int snd_pcm_start | ( | snd_pcm_t * | pcm | ) |
Start a PCM.
pcm | PCM handle |
snd_pcm_state_t snd_pcm_state | ( | snd_pcm_t * | pcm | ) |
Return PCM state.
pcm | PCM handle |
The function is thread-safe when built with the proper option.
int snd_pcm_status | ( | snd_pcm_t * | pcm, | |
snd_pcm_status_t * | status | |||
) |
Obtain status (runtime) information for PCM handle.
pcm | PCM handle | |
status | Status container |
snd_pcm_stream_t snd_pcm_stream | ( | snd_pcm_t * | pcm | ) |
get stream for a PCM handle
pcm | PCM handle |
int snd_pcm_sw_params | ( | snd_pcm_t * | pcm, | |
snd_pcm_sw_params_t * | params | |||
) |
Install PCM software configuration defined by params.
pcm | PCM handle | |
params | Configuration container |
The function is thread-safe when built with the proper option.
int snd_pcm_sw_params_current | ( | snd_pcm_t * | pcm, | |
snd_pcm_sw_params_t * | params | |||
) |
Return current software configuration for a PCM.
pcm | PCM handle | |
params | Software configuration container |
snd_pcm_type_t snd_pcm_type | ( | snd_pcm_t * | pcm | ) |
get type of PCM handle
pcm | PCM handle |
int snd_pcm_unlink | ( | snd_pcm_t * | pcm | ) |
Remove a PCM from a linked group.
pcm | PCM handle |
int snd_pcm_wait | ( | snd_pcm_t * | pcm, | |
int | timeout | |||
) |
Wait for a PCM to become ready.
pcm | PCM handle | |
timeout | maximum time in milliseconds to wait, a negative value means infinity |
0 | timeout occurred | |
1 | PCM stream is ready for I/O |
snd_pcm_sframes_t snd_pcm_writei | ( | snd_pcm_t * | pcm, | |
const void * | buffer, | |||
snd_pcm_uframes_t | size | |||
) |
Write interleaved frames to a PCM.
pcm | PCM handle | |
buffer | frames containing buffer | |
size | frames to be written |
-EBADFD | PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING) | |
-EPIPE | an underrun occurred | |
-ESTRPIPE | a suspend event occurred (stream is suspended and waiting for an application recovery) |
If the non-blocking behaviour is selected, then routine doesn't wait at all.
The function is thread-safe when built with the proper option.
snd_pcm_sframes_t snd_pcm_writen | ( | snd_pcm_t * | pcm, | |
void ** | bufs, | |||
snd_pcm_uframes_t | size | |||
) |
Write non interleaved frames to a PCM.
pcm | PCM handle | |
bufs | frames containing buffers (one for each channel) | |
size | frames to be written |
-EBADFD | PCM is not in the right state (SND_PCM_STATE_PREPARED or SND_PCM_STATE_RUNNING) | |
-EPIPE | an underrun occurred | |
-ESTRPIPE | a suspend event occurred (stream is suspended and waiting for an application recovery) |
If the non-blocking behaviour is selected, then routine doesn't wait at all.
The function is thread-safe when built with the proper option.