PipeWire 0.3.80
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Audio capture using pw_stream.

/* PipeWire */
/* SPDX-FileCopyrightText: Copyright © 2022 Wim Taymans */
/* SPDX-License-Identifier: MIT */
Audio capture using \ref pw_stream "pw_stream".
#include <stdio.h>
#include <errno.h>
#include <math.h>
#include <signal.h>
struct data {
struct pw_main_loop *loop;
struct pw_stream *stream;
struct spa_audio_info format;
unsigned move:1;
/* our data processing function is in general:
* struct pw_buffer *b;
* b = pw_stream_dequeue_buffer(stream);
* .. consume stuff in the buffer ...
* pw_stream_queue_buffer(stream, b);
static void on_process(void *userdata)
struct data *data = userdata;
struct pw_buffer *b;
struct spa_buffer *buf;
float *samples, max;
uint32_t c, n, n_channels, n_samples, peak;
if ((b = pw_stream_dequeue_buffer(data->stream)) == NULL) {
pw_log_warn("out of buffers: %m");
buf = b->buffer;
if ((samples = buf->datas[0].data) == NULL)
n_channels = data->format.info.raw.channels;
n_samples = buf->datas[0].chunk->size / sizeof(float);
/* move cursor up */
if (data->move)
fprintf(stdout, "%c[%dA", 0x1b, n_channels + 1);
fprintf(stdout, "captured %d samples\n", n_samples / n_channels);
for (c = 0; c < data->format.info.raw.channels; c++) {
max = 0.0f;
for (n = c; n < n_samples; n += n_channels)
max = fmaxf(max, fabsf(samples[n]));
peak = SPA_CLAMP(max * 30, 0, 39);
fprintf(stdout, "channel %d: |%*s%*s| peak:%f\n",
c, peak+1, "*", 40 - peak, "", max);
data->move = true;
pw_stream_queue_buffer(data->stream, b);
/* Be notified when the stream param changes. We're only looking at the
* format changes.
static void
on_stream_param_changed(void *_data, uint32_t id, const struct spa_pod *param)
struct data *data = _data;
/* NULL means to clear the format */
if (param == NULL || id != SPA_PARAM_Format)
if (spa_format_parse(param, &data->format.media_type, &data->format.media_subtype) < 0)
/* only accept raw audio */
if (data->format.media_type != SPA_MEDIA_TYPE_audio ||
data->format.media_subtype != SPA_MEDIA_SUBTYPE_raw)
/* call a helper function to parse the format for us. */
spa_format_audio_raw_parse(param, &data->format.info.raw);
fprintf(stdout, "capturing rate:%d channels:%d\n",
data->format.info.raw.rate, data->format.info.raw.channels);
static const struct pw_stream_events stream_events = {
.param_changed = on_stream_param_changed,
.process = on_process,
static void do_quit(void *userdata, int signal_number)
struct data *data = userdata;
int main(int argc, char *argv[])
struct data data = { 0, };
const struct spa_pod *params[1];
uint8_t buffer[1024];
struct pw_properties *props;
struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buffer, sizeof(buffer));
pw_init(&argc, &argv);
/* make a main loop. If you already have another main loop, you can add
* the fd of this pipewire mainloop to it. */
data.loop = pw_main_loop_new(NULL);
pw_loop_add_signal(pw_main_loop_get_loop(data.loop), SIGTERM, do_quit, &data);
/* Create a simple stream, the simple stream manages the core and remote
* objects for you if you don't need to deal with them.
* If you plan to autoconnect your stream, you need to provide at least
* media, category and role properties.
* Pass your events and a user_data pointer as the last arguments. This
* will inform you about the stream state. The most important event
* you need to listen to is the process event where you need to produce
* the data.
if (argc > 1)
/* Set stream target if given on command line */
/* uncomment if you want to capture from the sink monitor ports */
/* pw_properties_set(props, PW_KEY_STREAM_CAPTURE_SINK, "true"); */
/* Make one parameter with the supported formats. The SPA_PARAM_EnumFormat
* id means that this is a format enumeration (of 1 value).
* We leave the channels and rate empty to accept the native graph
* rate and channels. */
.format = SPA_AUDIO_FORMAT_F32));
/* Now connect this stream. We ask that our process function is
* called in a realtime thread. */
params, 1);
/* and wait while we let things run */
return 0;
#define PW_ID_ANY
Definition: core.h:66
Definition: src/pipewire/keys.h:431
a target object to link to.
Definition: src/pipewire/keys.h:496
Role: Movie, Music, Camera, Screen, Communication, Game, Notification, DSP, Production,...
Definition: src/pipewire/keys.h:437
Media Category: Playback, Capture, Duplex, Monitor, Manager.
Definition: src/pipewire/keys.h:434
#define pw_log_warn(...)
Definition: src/pipewire/log.h:143
#define pw_loop_add_signal(l,...)
Definition: src/pipewire/loop.h:63
int pw_main_loop_quit(struct pw_main_loop *loop)
Quit a main loop.
Definition: main-loop.c:105
void pw_main_loop_destroy(struct pw_main_loop *loop)
Destroy a loop.
Definition: main-loop.c:70
int pw_main_loop_run(struct pw_main_loop *loop)
Run a main loop.
Definition: main-loop.c:119
struct pw_main_loop * pw_main_loop_new(const struct spa_dict *props)
Create a new main loop.
Definition: main-loop.c:60
struct pw_loop * pw_main_loop_get_loop(struct pw_main_loop *loop)
Get the loop implementation.
Definition: main-loop.c:93
void pw_init(int *argc, char **argv[])
Initialize PipeWire.
Definition: pipewire.c:555
void pw_deinit(void)
Deinitialize PipeWire.
Definition: pipewire.c:668
Definition: port.h:48
struct pw_properties * pw_properties_new(const char *key,...) 1
Make a new properties object.
Definition: properties.c:84
int pw_properties_set(struct pw_properties *properties, const char *key, const char *value)
Set a property value.
Definition: properties.c:421
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:1882
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:2385
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:2413
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:1581
Definition: stream.h:330
void pw_stream_destroy(struct pw_stream *stream)
Destroy a stream.
Definition: stream.c:1675
mmap the buffers except DmaBuf
Definition: stream.h:378
try to automatically connect this stream
Definition: stream.h:373
call process from the realtime thread.
Definition: stream.h:380
static struct spa_pod * spa_format_audio_raw_build(struct spa_pod_builder *builder, uint32_t id, struct spa_audio_info_raw *info)
Definition: audio/raw-utils.h:47
static int spa_format_parse(const struct spa_pod *format, uint32_t *media_type, uint32_t *media_subtype)
Definition: format-utils.h:27
static int spa_format_audio_raw_parse(const struct spa_pod *format, struct spa_audio_info_raw *info)
Definition: audio/raw-utils.h:28
Definition: audio/raw.h:293
Definition: param/format.h:27
@ SPA_PARAM_Format
configured format as SPA_TYPE_OBJECT_Format
Definition: param.h:34
@ SPA_PARAM_EnumFormat
available formats as SPA_TYPE_OBJECT_Format
Definition: param.h:33
Definition: param/format.h:38
Definition: audio/raw.h:106
#define SPA_POD_BUILDER_INIT(buffer, size)
Definition: builder.h:62
#define SPA_CLAMP(v, low, high)
Definition: defs.h:163
a buffer structure obtained from pw_stream_dequeue_buffer().
Definition: stream.h:194
struct spa_buffer * buffer
the spa buffer
Definition: stream.h:195
A main loop object.
Definition: properties.h:33
Events for a stream.
Definition: stream.h:328
Definition: param/audio/format.h:38
A Buffer.
Definition: buffer/buffer.h:90
struct spa_data * datas
array of data members
Definition: buffer/buffer.h:94
uint32_t size
size of valid data.
Definition: buffer/buffer.h:47
struct spa_chunk * chunk
valid chunk of memory
Definition: buffer/buffer.h:86
void * data
optional data pointer
Definition: buffer/buffer.h:85
Definition: builder.h:53
void * data
Definition: builder.h:54
Definition: pod/pod.h:43