PipeWire  0.3.40

Tutorial - Part 4: Playing a tone

\ref page_tutorial4
/* [code] */
#include <math.h>
#define M_PI_M2 ( M_PI + M_PI )
#define DEFAULT_RATE 44100
#define DEFAULT_VOLUME 0.7
struct data {
struct pw_main_loop *loop;
struct pw_stream *stream;
double accumulator;
/* [on_process] */
static void on_process(void *userdata)
struct data *data = userdata;
struct pw_buffer *b;
struct spa_buffer *buf;
int i, c, n_frames, stride;
int16_t *dst, val;
if ((b = pw_stream_dequeue_buffer(data->stream)) == NULL) {
pw_log_warn("out of buffers: %m");
buf = b->buffer;
if ((dst = buf->datas[0].data) == NULL)
stride = sizeof(int16_t) * DEFAULT_CHANNELS;
n_frames = buf->datas[0].maxsize / stride;
for (i = 0; i < n_frames; i++) {
data->accumulator += M_PI_M2 * 440 / DEFAULT_RATE;
if (data->accumulator >= M_PI_M2)
data->accumulator -= M_PI_M2;
val = sin(data->accumulator) * DEFAULT_VOLUME * 16767.f;
for (c = 0; c < DEFAULT_CHANNELS; c++)
*dst++ = val;
buf->datas[0].chunk->offset = 0;
buf->datas[0].chunk->stride = stride;
buf->datas[0].chunk->size = n_frames * stride;
pw_stream_queue_buffer(data->stream, b);
/* [on_process] */
static const struct pw_stream_events stream_events = {
.process = on_process,
int main(int argc, char *argv[])
struct data data = { 0, };
const struct spa_pod *params[1];
uint8_t buffer[1024];
struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buffer, sizeof(buffer));
pw_init(&argc, &argv);
data.loop = pw_main_loop_new(NULL);
.rate = DEFAULT_RATE ));
argc > 1 ? (uint32_t)atoi(argv[1]) : PW_ID_ANY,
params, 1);
return 0;
/* [code] */
#define PW_ID_ANY
Definition: core.h:83
Definition: keys.h:415
Role: Movie, Music, Camera, Screen, Communication, Game, Notification, DSP, Production,...
Definition: keys.h:421
Media Category: Playback, Capture, Duplex, Monitor, Manager.
Definition: keys.h:418
#define pw_log_warn(...)
Definition: log.h:158
struct pw_main_loop * pw_main_loop_new(const struct spa_dict *props)
Create a new main loop.
Definition: main-loop.c:87
void pw_main_loop_destroy(struct pw_main_loop *loop)
Destroy a loop.
Definition: main-loop.c:97
int pw_main_loop_run(struct pw_main_loop *loop)
Run a main loop.
Definition: main-loop.c:146
struct pw_loop * pw_main_loop_get_loop(struct pw_main_loop *loop)
Get the loop implementation.
Definition: main-loop.c:120
void pw_init(int *argc, char **argv[])
Initialize PipeWire.
Definition: pipewire.c:586
Definition: port.h:67
struct pw_properties * pw_properties_new(const char *key,...) 1
Make a new properties object.
Definition: properties.c:102
int pw_stream_connect(struct pw_stream *stream, enum pw_direction direction, uint32_t target_id, enum pw_stream_flags flags, const struct spa_pod **params, uint32_t n_params)
Connect a stream for input or output on port_path.
Definition: stream.c:1663
struct pw_stream * pw_stream_new_simple(struct pw_loop *loop, const char *name, struct pw_properties *props, const struct pw_stream_events *events, void *data)
Definition: stream.c:1417
struct pw_buffer * pw_stream_dequeue_buffer(struct pw_stream *stream)
Get a buffer that can be filled for playback streams or consumed for capture streams.
Definition: stream.c:2080
int pw_stream_queue_buffer(struct pw_stream *stream, struct pw_buffer *buffer)
Submit a buffer for playback or recycle a buffer for capture.
Definition: stream.c:2107
Definition: stream.h:219
void pw_stream_destroy(struct pw_stream *stream)
Destroy a stream.
Definition: stream.c:1479
mmap the buffers except DmaBuf
Definition: stream.h:267
try to automatically connect this stream
Definition: stream.h:262
call process from the realtime thread.
Definition: stream.h:269
static struct spa_pod * spa_format_audio_raw_build(struct spa_pod_builder *builder, uint32_t id, struct spa_audio_info_raw *info)
Definition: format-utils.h:108
Definition: raw.h:307
@ SPA_PARAM_EnumFormat
available formats as SPA_TYPE_OBJECT_Format
Definition: param.h:53
Definition: raw.h:114
#define SPA_POD_BUILDER_INIT(buffer, size)
Definition: builder.h:82
Definition: stream.h:181
struct spa_buffer * buffer
the spa buffer
Definition: stream.h:182
A main loop object.
Events for a stream.
Definition: stream.h:217
A Buffer.
Definition: buffer.h:105
struct spa_data * datas
array of data members
Definition: buffer.h:109
int32_t stride
stride of valid data
Definition: buffer.h:68
uint32_t size
size of valid data.
Definition: buffer.h:66
uint32_t offset
offset of valid data.
Definition: buffer.h:63
struct spa_chunk * chunk
valid chunk of memory
Definition: buffer.h:101
void * data
optional data pointer
Definition: buffer.h:100
uint32_t maxsize
max size of data
Definition: buffer.h:99
Definition: builder.h:73
void * data
Definition: builder.h:74
Definition: pod.h:63