Add ALSA PCM devices and option to set channels

Fixes #262

src/engine/alsapcmdevicefinder.cpp

@@ -0,0 +1,85 @@
+/*
+ * Strawberry Music Player
+ * Copyright 2021, Jonas Kvinge <jonas@jkvinge.net>
+ *
+ * Strawberry is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Strawberry is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with Strawberry.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "config.h"
+
+#include <cstdio>
+#include <cerrno>
+#include <alsa/asoundlib.h>
+
+#include <QList>
+#include <QVariant>
+#include <QString>
+#include <QtDebug>
+
+#include <core/logging.h>
+
+#include "devicefinder.h"
+#include "alsapcmdevicefinder.h"
+
+AlsaPCMDeviceFinder::AlsaPCMDeviceFinder()
+    : DeviceFinder("alsa", {"alsa","alsasink"}) {}
+
+QList<DeviceFinder::Device> AlsaPCMDeviceFinder::ListDevices() {
+
+  QList<Device> ret;
+
+  void **hints = nullptr;
+  if (snd_device_name_hint(-1, "pcm", &hints) < 0) {
+    return ret;
+  }
+
+  for (void **n = hints ; *n ; ++n) {
+    char *io = snd_device_name_get_hint(*n, "IOID");
+    char *name = snd_device_name_get_hint(*n, "NAME");
+    char *desc = snd_device_name_get_hint(*n, "DESC");
+    if (io && name && desc && strcmp(io, "Output") == 0) {
+
+      char *desc_last = desc;
+      QString description;
+      for (char *desc_i = desc ; desc_i && *desc_i != '\0' ; ++desc_i) {
+        if (*desc_i == '\n') {
+          *desc_i = '\0';
+          if (!description.isEmpty()) description.append(' ');
+          description.append(desc_last);
+          desc_last = desc_i + 1;
+        }
+      }
+
+      if (desc_last) {
+        if (!description.isEmpty()) description.append(' ');
+        description.append(desc_last);
+      }
+
+      Device device;
+      device.value = name;
+      device.description = description;
+      device.iconname = GuessIconName(device.description);
+      ret << device;
+    }
+    if (io) free(io);
+    if (name) free(name);
+    if (desc) free(desc);
+  }
+
+  snd_device_name_free_hint(hints);
+
+  return ret;
+
+}