examples: add audio source with ringbuffer

Add an example of a stream that plays data from a ringbuffer that is
filled from some other thread.

src/examples/audio-src-ring.c

@@ -0,0 +1,219 @@
+/* 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;
+        }
+}
+
+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 ...
+ *
+ *  pw_stream_queue_buffer(stream, b);
+ */
+static void on_process(void *userdata)
+{
+	struct data *data = userdata;
+	struct pw_buffer *b;
+	struct spa_buffer *buf;
+	int n_frames, stride;
+	uint8_t *p;
+	uint32_t index;
+	int32_t avail;
+
+	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((int)b->requested, n_frames);
+
+	if (avail < (int32_t)n_frames) {
+		/* there is not enough data available in the ringbuffer,
+		 * fill with silence and hope it will be filled next time */
+		memset(p, 0, n_frames * stride);
+		pw_log_warn("underrun");
+	} else {
+		/* enough data in the ringbuffer, copy it into the buffer data.
+		 * We use the number of samples as the read/write counters so we
+		 * need to multiply with the stride to get the byte offsets. */
+		spa_ringbuffer_read_data(&data->ring,
+				data->buffer, BUFFER_SIZE * stride,
+				(index % BUFFER_SIZE) * stride,
+				p, n_frames * stride);
+		/* update the read pointer */
+		spa_ringbuffer_read_update(&data->ring, index + n_frames);
+
+	}
+	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 */
+	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_main_loop_destroy(data.main_loop);
+	pw_deinit();
+
+	return 0;
+}

src/examples/meson.build

@@ -1,6 +1,7 @@
 # Examples, in order from simple to complicated
 examples = [
   'audio-src',
+  'audio-src-ring',
   'audio-dsp-src',
   'audio-dsp-filter',
   'audio-capture',