Merge branch 'null-always-off' of https://github.com/nomis/MPD

NEWS

@@ -33,6 +33,7 @@ ver 0.24 (not yet released)
 * tags
   - new tags "TitleSort", "Mood"
 * output
+  - add option "always_off"
   - alsa: require alsa-lib 1.1 or later
   - pipewire: map tags "Date" and "Comment"
 * switch to C++20

doc/user.rst

@@ -517,6 +517,11 @@ The following table lists the audio_output options valid for all plugins:
      - If set to no, then :program:`MPD` will not send tags to this output. This is only useful for output plugins that can receive tags, for example the httpd output plugin.
    * - **always_on yes|no**
      - If set to yes, then :program:`MPD` attempts to keep this audio output always open. This may be useful for streaming servers, when you don't want to disconnect all listeners even when playback is accidentally stopped.
+   * - **always_off yes|no**
+     - If set to yes, then :program:`MPD` never uses this audio output for
+       playback even if it's enabled. This can be used with the null output
+       plugin to create placeholder outputs for other software to react to
+       the enabled state without affecting playback.
    * - **mixer_type hardware|software|null|none**
      - Specifies which mixer should be used for this audio output: the
        hardware mixer (available for ALSA :ref:`alsa_plugin`, OSS

src/output/Control.cxx

@@ -25,6 +25,7 @@ AudioOutputControl::AudioOutputControl(std::unique_ptr<FilteredAudioOutput> _out
 	 thread(BIND_THIS_METHOD(Task)),
 	 tags(block.GetBlockValue("tags", true)),
 	 always_on(block.GetBlockValue("always_on", false)),
+	 always_off(block.GetBlockValue("always_off", false)),
 	 enabled(block.GetBlockValue("enabled", true))
 {
 }
@@ -36,7 +37,8 @@ AudioOutputControl::AudioOutputControl(AudioOutputControl &&src,
 	 client(_client),
 	 thread(BIND_THIS_METHOD(Task)),
 	 tags(src.tags),
-	 always_on(src.always_on)
+	 always_on(src.always_on),
+	 always_off(src.always_off)
 {
 }
 
@@ -176,6 +178,9 @@ AudioOutputControl::EnableAsync()
 	if (!output)
 		return;
 
+	if (always_off)
+		return;
+
 	if (!thread.IsDefined()) {
 		if (!output->SupportsEnableDisable()) {
 			/* don't bother to start the thread now if the

src/output/Control.hxx

@@ -143,6 +143,11 @@ class AudioOutputControl {
 	 */
 	const bool always_on;
 
+	/**
+	 * Should this output never play anything, even when enabled?
+	 */
+	const bool always_off;
+
 	/**
 	 * Has the user enabled this device?
 	 */
@@ -274,6 +279,10 @@ public:
 		return !output;
 	}
 
+	bool AlwaysOff() const noexcept {
+		return always_off;
+	}
+
 	/**
 	 * Caller must lock the mutex.
 	 */

src/output/MultipleOutputs.cxx

@@ -215,6 +215,10 @@ MultipleOutputs::Open(const AudioFormat audio_format)
 	for (const auto &ao : outputs) {
 		const std::scoped_lock<Mutex> lock(ao->mutex);
 
+		/* can't play on this device even if it's enabled */
+		if (ao->AlwaysOff())
+			continue;
+
 		if (ao->IsEnabled())
 			enabled = true;