A clear explanation seems to be missing in the PulseAudio documentation, and I cannot find any simple examples.
Like so
/*
pcm-playback: pcm-playback.c
gcc -o pcm-playback pcm-playback.c `pkg-config --cflags --libs libpulse`
*/
#include <stdio.h>
#include <assert.h>
#include <pulse/pulseaudio.h>
#define FORMAT PA_SAMPLE_U8
#define RATE 44100
void context_state_cb(pa_context* context, void* mainloop);
void stream_state_cb(pa_stream *s, void *mainloop);
void stream_success_cb(pa_stream *stream, int success, void *userdata);
void stream_write_cb(pa_stream *stream, size_t requested_bytes, void *userdata);
int main(int argc, char *argv[]) {
pa_threaded_mainloop *mainloop;
pa_mainloop_api *mainloop_api;
pa_context *context;
pa_stream *stream;
// Get a mainloop and its context
mainloop = pa_threaded_mainloop_new();
assert(mainloop);
mainloop_api = pa_threaded_mainloop_get_api(mainloop);
context = pa_context_new(mainloop_api, "pcm-playback");
assert(context);
// Set a callback so we can wait for the context to be ready
pa_context_set_state_callback(context, &context_state_cb, mainloop);
// Lock the mainloop so that it does not run and crash before the context is ready
pa_threaded_mainloop_lock(mainloop);
// Start the mainloop
assert(pa_threaded_mainloop_start(mainloop) == 0);
assert(pa_context_connect(context, NULL, PA_CONTEXT_NOAUTOSPAWN, NULL) == 0);
// Wait for the context to be ready
for(;;) {
pa_context_state_t context_state = pa_context_get_state(context);
assert(PA_CONTEXT_IS_GOOD(context_state));
if (context_state == PA_CONTEXT_READY) break;
pa_threaded_mainloop_wait(mainloop);
}
// Create a playback stream
pa_sample_spec sample_specifications;
sample_specifications.format = FORMAT;
sample_specifications.rate = RATE;
sample_specifications.channels = 2;
pa_channel_map map;
pa_channel_map_init_stereo(&map);
stream = pa_stream_new(context, "Playback", &sample_specifications, &map);
pa_stream_set_state_callback(stream, stream_state_cb, mainloop);
pa_stream_set_write_callback(stream, stream_write_cb, mainloop);
// recommended settings, i.e. server uses sensible values
pa_buffer_attr buffer_attr;
buffer_attr.maxlength = (uint32_t) -1;
buffer_attr.tlength = (uint32_t) -1;
buffer_attr.prebuf = (uint32_t) -1;
buffer_attr.minreq = (uint32_t) -1;
// Settings copied as per the chromium browser source
pa_stream_flags_t stream_flags;
stream_flags = PA_STREAM_START_CORKED | PA_STREAM_INTERPOLATE_TIMING |
PA_STREAM_NOT_MONOTONIC | PA_STREAM_AUTO_TIMING_UPDATE |
PA_STREAM_ADJUST_LATENCY;
// Connect stream to the default audio output sink
assert(pa_stream_connect_playback(stream, NULL, &buffer_attr, stream_flags, NULL, NULL) == 0);
// Wait for the stream to be ready
for(;;) {
pa_stream_state_t stream_state = pa_stream_get_state(stream);
assert(PA_STREAM_IS_GOOD(stream_state));
if (stream_state == PA_STREAM_READY) break;
pa_threaded_mainloop_wait(mainloop);
}
pa_threaded_mainloop_unlock(mainloop);
// Uncork the stream so it will start playing
pa_stream_cork(stream, 0, stream_success_cb, mainloop);
// Play until we get a character
getc(stdin);
}
void context_state_cb(pa_context* context, void* mainloop) {
pa_threaded_mainloop_signal(mainloop, 0);
}
void stream_state_cb(pa_stream *s, void *mainloop) {
pa_threaded_mainloop_signal(mainloop, 0);
}
void stream_write_cb(pa_stream *stream, size_t requested_bytes, void *userdata) {
int bytes_remaining = requested_bytes;
while (bytes_remaining > 0) {
uint8_t *buffer = NULL;
size_t bytes_to_fill = 44100;
size_t i;
if (bytes_to_fill > bytes_remaining) bytes_to_fill = bytes_remaining;
pa_stream_begin_write(stream, (void**) &buffer, &bytes_to_fill);
for (i = 0; i < bytes_to_fill; i += 2) {
buffer[i] = (i%100) * 40 / 100 + 44;
buffer[i+1] = (i%100) * 40 / 100 + 44;
}
pa_stream_write(stream, buffer, bytes_to_fill, NULL, 0LL, PA_SEEK_RELATIVE);
bytes_remaining -= bytes_to_fill;
}
}
void stream_success_cb(pa_stream *stream, int success, void *userdata) {
return;
}
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