From c19abd24ee5929934a88adf1dd86107fc0cd5f61 Mon Sep 17 00:00:00 2001
From: "Steinar H. Gunderson" <sgunderson@bigfoot.com>
Date: Sat, 10 Sep 2016 14:06:54 +0200
Subject: [PATCH] When an ALSA input goes away, replace it by silence.

Silences the warning spew from the resampler that no data is coming.
---
 alsa_input.cpp  | 17 +++++++++++++++--
 audio_mixer.cpp | 30 +++++++++++++++++++++++++-----
 audio_mixer.h   |  8 ++++++++
 3 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/alsa_input.cpp b/alsa_input.cpp
index a6487a4..0a39d3f 100644
--- a/alsa_input.cpp
+++ b/alsa_input.cpp
@@ -166,6 +166,8 @@ void ALSAInput::stop_capture_thread()
 
 void ALSAInput::capture_thread_func()
 {
+	parent_pool->set_card_state(internal_dev_index, ALSAPool::Device::State::STARTING);
+
 	// If the device hasn't been opened already, we need to do so
 	// before we can capture.
 	while (!should_quit && pcm_handle == nullptr) {
@@ -549,8 +551,15 @@ ALSAPool::Device::State ALSAPool::get_card_state(unsigned index)
 
 void ALSAPool::set_card_state(unsigned index, ALSAPool::Device::State state)
 {
-	lock_guard<mutex> lock(mu);
-	devices[index].state = state;
+	{
+		lock_guard<mutex> lock(mu);
+		devices[index].state = state;
+	}
+
+	DeviceSpec spec{InputSourceType::ALSA_INPUT, index};
+	bool silence = (state != ALSAPool::Device::State::RUNNING);
+	while (!global_audio_mixer->silence_card(spec, silence))
+		;
 }
 
 unsigned ALSAPool::find_free_device_index()
@@ -570,6 +579,10 @@ unsigned ALSAPool::find_free_device_index()
 
 void ALSAPool::free_card(unsigned index)
 {
+	DeviceSpec spec{InputSourceType::ALSA_INPUT, index};
+	while (!global_audio_mixer->silence_card(spec, true))
+		;
+
 	lock_guard<mutex> lock(mu);
 	if (devices[index].held) {
 		devices[index].state = Device::State::DEAD;
diff --git a/audio_mixer.cpp b/audio_mixer.cpp
index 8485d0a..87a99bd 100644
--- a/audio_mixer.cpp
+++ b/audio_mixer.cpp
@@ -294,6 +294,22 @@ bool AudioMixer::add_silence(DeviceSpec device_spec, unsigned samples_per_frame,
 	return true;
 }
 
+bool AudioMixer::silence_card(DeviceSpec device_spec, bool silence)
+{
+	AudioDevice *device = find_audio_device(device_spec);
+
+	unique_lock<timed_mutex> lock(audio_mutex, defer_lock);
+	if (!lock.try_lock_for(chrono::milliseconds(10))) {
+		return false;
+	}
+
+	if (device->silenced && !silence) {
+		reset_resampler_mutex_held(device_spec);
+	}
+	device->silenced = silence;
+	return true;
+}
+
 AudioMixer::AudioDevice *AudioMixer::find_audio_device(DeviceSpec device)
 {
 	switch (device.type) {
@@ -383,11 +399,15 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
 	for (const DeviceSpec &device_spec : get_active_devices()) {
 		AudioDevice *device = find_audio_device(device_spec);
 		samples_card[device_spec].resize(num_samples * device->interesting_channels.size());
-		device->resampling_queue->get_output_samples(
-			pts,
-			&samples_card[device_spec][0],
-			num_samples,
-			rate_adjustment_policy);
+		if (device->silenced) {
+			memset(&samples_card[device_spec][0], 0, samples_card[device_spec].size() * sizeof(float));
+		} else {
+			device->resampling_queue->get_output_samples(
+				pts,
+				&samples_card[device_spec][0],
+				num_samples,
+				rate_adjustment_policy);
+		}
 	}
 
 	vector<float> samples_out, left, right;
diff --git a/audio_mixer.h b/audio_mixer.h
index c845a26..855295d 100644
--- a/audio_mixer.h
+++ b/audio_mixer.h
@@ -93,6 +93,13 @@ public:
 	bool add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, bmusb::AudioFormat audio_format, int64_t frame_length);
 	bool add_silence(DeviceSpec device_spec, unsigned samples_per_frame, unsigned num_frames, int64_t frame_length);
 
+	// If a given device is offline for whatever reason and cannot deliver audio
+	// (by means of add_audio() or add_silence()), you can call put it in silence mode,
+	// where it will be taken to only output silence. Note that when taking it _out_
+	// of silence mode, the resampler will be reset, so that old audio will not
+	// affect it. Same true/false behavior as add_audio().
+	bool silence_card(DeviceSpec device_spec, bool silence);
+
 	std::vector<float> get_output(double pts, unsigned num_samples, ResamplingQueue::RateAdjustmentPolicy rate_adjustment_policy);
 
 	void set_fader_volume(unsigned bus_index, float level_db) { fader_volume_db[bus_index] = level_db; }
@@ -263,6 +270,7 @@ private:
 		unsigned capture_frequency = OUTPUT_FREQUENCY;
 		// Which channels we consider interesting (ie., are part of some input_mapping).
 		std::set<unsigned> interesting_channels;
+		bool silenced = false;
 	};
 
 	const AudioDevice *find_audio_device(DeviceSpec device_spec) const
-- 
2.39.2