pipewire: Add experimental PipeWire support

This implements a PipeWire capture device which can be used as an input
source instead of the already available URL input.

Known issues with the current PipeWire support are:

- user has to connect the monitor of the default audio sink to the
  capture device manually
- correct shutdown has to be tested
- multiple instances do not work
- medium code quality requires refactoring

Since this is nevertheless usable and possible unknown bugs should be
figured out in practise soon this implementation is already added.
Bugfixes and refactoring might follow.

5 files changed, 237 insertions, 0 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7e37669..f7e58e8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,13 @@ The format is based on [Keep a Changelog][keep-a-changelog], and this project
 adheres to [Semantic Versioning][semantic-versioning].
 
 
+## [Unreleased][unreleased]
+
+### Added
+
+- streaming any audio content via PipeWire capture device on Linux
+
+
 ## [Version 0.1.5][0.1.5] - 2024-11-29
 
 ### Fixed
diff --git a/soundbox/pipewire-binding.c b/soundbox/pipewire-binding.c
new file mode 100644
index 0000000..bb10e31
--- /dev/null
+++ b/soundbox/pipewire-binding.c
@@ -0,0 +1,105 @@
+#include <pipewire/pipewire.h>
+#include <spa/param/audio/format-utils.h>
+
+#include "pipewire-binding.h"
+
+
+#define SAMPLING_RATE 48000
+#define CHANNELS      2
+#define VOLUME        0.7
+#define NODE_NAME     "soundbox"
+#define STRIDE        sizeof(int16_t) * CHANNELS
+
+
+static void on_process(void *userdata)
+{
+	struct pw_stream *stream = *(struct pw_stream **)userdata;
+	struct pw_buffer *pw_buf;
+	struct spa_buffer *spa_buf;
+	int n_frames;
+	int16_t *src;
+
+	if ((pw_buf = pw_stream_dequeue_buffer(stream)) == NULL) {
+		return;
+	}
+
+	spa_buf = pw_buf->buffer;
+	if ((src = spa_buf->datas[0].data) == NULL) {
+		return;
+	}
+
+	n_frames = spa_buf->datas[0].chunk->size / STRIDE;
+	if (pw_buf->requested) {
+		n_frames = SPA_MIN(pw_buf->requested, n_frames);
+	}
+
+	size_t len = spa_buf->datas[0].chunk->size;
+
+	goHandleData(src, len);
+
+	spa_buf->datas[0].chunk->offset = 0;
+	spa_buf->datas[0].chunk->stride = STRIDE;
+	spa_buf->datas[0].chunk->size = n_frames * STRIDE;
+
+	pw_stream_queue_buffer(stream, pw_buf);
+}
+
+
+static const struct pw_stream_events stream_events = {
+	PW_VERSION_STREAM_EVENTS,
+	.process = on_process,
+};
+
+
+void pw_stdout(void)
+{
+	pw_init(NULL, NULL);
+
+	struct pw_main_loop *loop = pw_main_loop_new(NULL);
+
+	struct pw_stream *stream = NULL;
+	stream = pw_stream_new_simple(
+		pw_main_loop_get_loop(loop),
+		NODE_NAME,
+		pw_properties_new(
+			PW_KEY_MEDIA_TYPE, "Audio",
+			PW_KEY_CONFIG_NAME, "client-rt.conf",
+			PW_KEY_MEDIA_CATEGORY, "Capture",
+			PW_KEY_MEDIA_ROLE, "Music",
+			NULL
+		),
+		&stream_events,
+		&stream
+	);
+
+	uint8_t buffer[1024];
+	struct spa_pod_builder b = SPA_POD_BUILDER_INIT(buffer, sizeof(buffer));
+	const struct spa_pod *params[] = {
+		spa_format_audio_raw_build(
+			&b,
+			SPA_PARAM_EnumFormat,
+			&SPA_AUDIO_INFO_RAW_INIT(
+				.format = SPA_AUDIO_FORMAT_S16,
+				.channels = CHANNELS,
+				.rate = SAMPLING_RATE
+			)
+		)
+	};
+
+	pw_stream_connect(
+		stream,
+		PW_DIRECTION_INPUT,
+		PW_ID_ANY,
+		PW_STREAM_FLAG_AUTOCONNECT |
+		PW_STREAM_FLAG_MAP_BUFFERS |
+		PW_STREAM_FLAG_RT_PROCESS,
+		params,
+		sizeof(params) / sizeof(params[0])
+	);
+
+	pw_main_loop_run(loop);
+
+	pw_stream_destroy(stream);
+	pw_main_loop_destroy(loop);
+	pw_deinit();
+}
diff --git a/soundbox/pipewire-binding.h b/soundbox/pipewire-binding.h
new file mode 100644
index 0000000..d25a0b9
--- /dev/null
+++ b/soundbox/pipewire-binding.h
@@ -0,0 +1,10 @@
+#ifndef PIPEWIRE_BINDING_H
+#define PIPEWIRE_BINDING_H
+
+#include <stdint.h>
+#include <stddef.h>
+
+extern void goHandleData(int16_t *, size_t);
+void pw_stdout(void);
+
+#endif // !PIPEWIRE_BINDING_H
diff --git a/soundbox/pipewire.go b/soundbox/pipewire.go
new file mode 100644
index 0000000..fbae73b
--- /dev/null
+++ b/soundbox/pipewire.go
@@ -0,0 +1,80 @@
+package soundbox
+
+/*
+#cgo pkg-config: libpipewire-0.3
+#include "pipewire-binding.h"
+*/
+import "C"
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"net"
+	"log"
+	"os/exec"
+	"unsafe"
+)
+
+var pipewireAudio = make(chan []byte, 5)
+
+func StreamPipewireContext(ctx context.Context, targets []net.HardwareAddr) error {
+	cmd := exec.CommandContext(
+		ctx,
+		"ffmpeg",
+		"-ac",
+		"2",
+		"-ar",
+		"48000",
+		"-f",
+		"s16le",
+		"-channel_layout",
+		"stereo",
+		"-i",
+		"-",
+		"-acodec",
+		"flac",
+		"-f",
+		"ogg",
+		"-",
+	)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+	stdin, err := cmd.StdinPipe()
+	if err != nil {
+		return err
+	}
+
+	go C.pw_stdout()
+
+	go func() {
+		for buffer := range pipewireAudio {
+			tempReader := bytes.NewReader(buffer)
+			_, err := io.Copy(stdin, tempReader)
+			if err != nil {
+				log.Println("Failed to copy from PipeWire to ffmpeg.")
+				break
+			}
+		}
+	}()
+
+	err = cmd.Start()
+	if err != nil {
+		return err
+	}
+
+	err = streamContext(ctx, stdout, targets)
+	if err != nil {
+		return err
+	}
+
+	return cmd.Wait()
+}
+
+//export goHandleData
+func goHandleData(data *C.int16_t, size C.size_t) {
+	buf := C.GoBytes(unsafe.Pointer(data), C.int(size))
+	pipewireAudio <- buf
+}
diff --git a/soundbox/pipewire_test.go b/soundbox/pipewire_test.go
new file mode 100644
index 0000000..b857414
--- /dev/null
+++ b/soundbox/pipewire_test.go
@@ -0,0 +1,35 @@
+package soundbox_test
+
+import (
+	"context"
+	"log"
+	"net"
+	"time"
+
+	"xengineering.eu/soundbox-go/soundbox"
+)
+
+func ExampleStreamPipewireContext() {
+	ctx, cancel := context.WithCancel(context.Background())
+
+	// all soundboxes are referenced by their MAC address
+	soundboxes := []net.HardwareAddr{
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x01},
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x02},
+		{0x00, 0x00, 0x5E, 0x00, 0x53, 0x03},
+	}
+
+	// start streaming
+	go func() {
+		err := soundbox.StreamPipewireContext(ctx, soundboxes)
+		if err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// let it play for some time
+	time.Sleep(time.Minute)
+
+	// stop it
+	cancel()
+}