audio-src-ring.c

doc} audio-src-ring.c title
doc} audio-src-ring.c doc

/* PipeWire */
/* SPDX-FileCopyrightText: Copyright © 2024 Wim Taymans */
/* SPDX-License-Identifier: MIT */

/*
 [title]
 Audio source using \ref pw_stream "pw_stream" and ringbuffer.
 [title]
 */

#include <stdio.h>
#include <errno.h>
#include <math.h>
#include <signal.h>

#include <spa/param/audio/format-utils.h>
#include <spa/utils/ringbuffer.h>

#include <pipewire/pipewire.h>

#define M_PI_M2f (float)(M_PI+M_PI)

#define DEFAULT_RATE            44100
#define DEFAULT_CHANNELS        2
#define DEFAULT_VOLUME          0.7f

#define BUFFER_SIZE             (16*1024)

struct data {
        struct pw_main_loop *main_loop;
        struct pw_loop *loop;
        struct pw_stream *stream;

        float accumulator;

        struct spa_source *refill_event;

        struct spa_ringbuffer ring;
        float buffer[BUFFER_SIZE * DEFAULT_CHANNELS];
};

static void fill_f32(struct data *d, uint32_t offset, int n_frames)
{
        float val;
        int i, c;

        for (i = 0; i < n_frames; i++) {
                d->accumulator += M_PI_M2f * 440 / DEFAULT_RATE;
                if (d->accumulator >= M_PI_M2f)
                        d->accumulator -= M_PI_M2f;

                val = sinf(d->accumulator) * DEFAULT_VOLUME;
                for (c = 0; c < DEFAULT_CHANNELS; c++)
                        d->buffer[((offset + i) % BUFFER_SIZE) * DEFAULT_CHANNELS + c] = val;
        }
}

/* this is called from the main-thread when we need to fill up the ringbuffer
 * with more data */
static void do_refill(void *userdata, uint64_t count)
{
        struct data *data = userdata;
        int32_t filled;
        uint32_t index, avail;

        filled = spa_ringbuffer_get_write_index(&data->ring, &index);
        /* we xrun, this can not happen because we never read more
         * than what there is in the ringbuffer and we never write more than
         * what is left */
        spa_assert(filled >= 0);
        spa_assert(filled <= BUFFER_SIZE);

        /* this is how much samples we can write */
        avail = BUFFER_SIZE - filled;

        /* write new samples to the ringbuffer from the given index */
        fill_f32(data, index, avail);

        /* and advance the ringbuffer */
        spa_ringbuffer_write_update(&data->ring, index + avail);
}

/* our data processing function is in general:
 *
 *  struct pw_buffer *b;
 *  b = pw_stream_dequeue_buffer(stream);
 *
 *  .. generate stuff in the buffer ...
 *  In this case we read samples from a ringbuffer. The ringbuffer is
 *  filled up by another thread.
 *
 *  pw_stream_queue_buffer(stream, b);
 */
static void on_process(void *userdata)
{
        struct data *data = userdata;
        struct pw_buffer *b;
        struct spa_buffer *buf;
        uint8_t *p;
        uint32_t index, to_read, to_silence;
        int32_t avail, n_frames, stride;

        if ((b = pw_stream_dequeue_buffer(data->stream)) == NULL) {
                pw_log_warn("out of buffers: %m");
                return;
        }

        buf = b->buffer;
        if ((p = buf->datas[0].data) == NULL)
                return;

        /* the amount of space in the ringbuffer and the read index */
        avail = spa_ringbuffer_get_read_index(&data->ring, &index);

        stride = sizeof(float) * DEFAULT_CHANNELS;
        n_frames = buf->datas[0].maxsize / stride;
        if (b->requested)
                n_frames = SPA_MIN((int32_t)b->requested, n_frames);

        /* we can read if there is something available */
        to_read = avail > 0 ? SPA_MIN(avail, n_frames) : 0;
        /* and fill the remainder with silence */
        to_silence = n_frames - to_read;

        if (to_read > 0) {
                /* read data into the buffer */
                spa_ringbuffer_read_data(&data->ring,
                                data->buffer, BUFFER_SIZE * stride,
                                (index % BUFFER_SIZE) * stride,
                                p, to_read * stride);
                /* update the read pointer */
                spa_ringbuffer_read_update(&data->ring, index + to_read);
        }
        if (to_silence > 0)
                /* set the rest of the buffer to silence */
                memset(SPA_PTROFF(p, to_read * stride, void), 0, to_silence * stride);

        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);

        /* signal the main thread to fill the ringbuffer, we can only do this, for
         * example when the available ringbuffer space falls below a certain
         * level. */
        pw_loop_signal_event(data->loop, data->refill_event);
}

static const struct pw_stream_events stream_events = {
        PW_VERSION_STREAM_EVENTS,
        .process = on_process,
};

static void do_quit(void *userdata, int signal_number)
{
        struct data *data = userdata;
        pw_main_loop_quit(data->main_loop);
}

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);

        data.main_loop = pw_main_loop_new(NULL);
        data.loop = pw_main_loop_get_loop(data.main_loop);

        pw_loop_add_signal(data.loop, SIGINT, do_quit, &data);
        pw_loop_add_signal(data.loop, SIGTERM, do_quit, &data);

        /* we're going to refill a ringbuffer from the main loop. Make an
         * event for this. */
        spa_ringbuffer_init(&data.ring);
        data.refill_event = pw_loop_add_event(data.loop, do_refill, &data);
        /* prefill the ringbuffer */
        do_refill(&data, 0);

        props = pw_properties_new(PW_KEY_MEDIA_TYPE, "Audio",
                        PW_KEY_MEDIA_CATEGORY, "Playback",
                        PW_KEY_MEDIA_ROLE, "Music",
                        NULL);
        if (argc > 1)
                /* Set stream target if given on command line */
                pw_properties_set(props, PW_KEY_TARGET_OBJECT, argv[1]);

        data.stream = pw_stream_new_simple(
                        data.loop,
                        "audio-src-ring",
                        props,
                        &stream_events,
                        &data);

        /* Make one parameter with the supported formats. The SPA_PARAM_EnumFormat
         * id means that this is a format enumeration (of 1 value). */
        params[0] = spa_format_audio_raw_build(&b, SPA_PARAM_EnumFormat,
                        &SPA_AUDIO_INFO_RAW_INIT(
                                .format = SPA_AUDIO_FORMAT_F32,
                                .channels = DEFAULT_CHANNELS,
                                .rate = DEFAULT_RATE ));

        /* Now connect this stream. We ask that our process function is
         * called in a realtime thread. */
        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);

        /* and wait while we let things run */
        pw_main_loop_run(data.main_loop);

        pw_stream_destroy(data.stream);
        pw_loop_destroy_source(data.loop, data.refill_event);
        pw_main_loop_destroy(data.main_loop);
        pw_deinit();

        return 0;
}