tutorial4.c

Tutorial - Part 4: Playing A Tone

/*
  [title]
  \ref page_tutorial4
  [title]
 */
/* [code] */
#include <math.h>
 
#include <spa/param/audio/format-utils.h>
 
#include <pipewire/pipewire.h>
 
#define M_PI_M2 ( M_PI + M_PI )
 
#define DEFAULT_RATE            44100
#define DEFAULT_CHANNELS        2
#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");
                return;
        }
 
        buf = b->buffer;
        if ((dst = buf->datas[0].data) == NULL)
                return;
 
        stride = sizeof(int16_t) * DEFAULT_CHANNELS;
        n_frames = buf->datas[0].maxsize / stride;
        if (b->requested)
                n_frames = SPA_MIN(b->requested, n_frames);
 
        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;
 
                /* sin() gives a value between -1.0 and 1.0, we first apply
                 * the volume and then scale with 32767.0 to get a 16 bits value
                 * between [-32767 32767].
                 * Another common method to convert a double to
                 * 16 bits is to multiple by 32768.0 and then clamp to
                 * [-32768 32767] to get the full 16 bits range. */
                val = sin(data->accumulator) * DEFAULT_VOLUME * 32767.0;
                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 = {
        PW_VERSION_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);
 
        data.stream = pw_stream_new_simple(
                        pw_main_loop_get_loop(data.loop),
                        "audio-src",
                        pw_properties_new(
                                PW_KEY_MEDIA_TYPE, "Audio",
                                PW_KEY_MEDIA_CATEGORY, "Playback",
                                PW_KEY_MEDIA_ROLE, "Music",
                                NULL),
                        &stream_events,
                        &data);
 
        params[0] = spa_format_audio_raw_build(&b, SPA_PARAM_EnumFormat,
                        &SPA_AUDIO_INFO_RAW_INIT(
                                .format = SPA_AUDIO_FORMAT_S16,
                                .channels = DEFAULT_CHANNELS,
                                .rate = DEFAULT_RATE ));
 
        pw_stream_connect(data.stream,
                          PW_DIRECTION_OUTPUT,
                          PW_ID_ANY,
                          PW_STREAM_FLAG_AUTOCONNECT |
                          PW_STREAM_FLAG_MAP_BUFFERS |
                          PW_STREAM_FLAG_RT_PROCESS,
                          params, 1);
 
        pw_main_loop_run(data.loop);
 
        pw_stream_destroy(data.stream);
        pw_main_loop_destroy(data.loop);
 
        return 0;
}
/* [code] */