]> git.sesse.net Git - nageru/blobdiff - audio_mixer.cpp
Write 1.4.0 changelog.
[nageru] / audio_mixer.cpp
index e28acfeb00154d2926e1f00c9fa26382c511aae8..e4d4cff4b86222e41d6b0d8181b8d519a1f1b6a1 100644 (file)
@@ -1,17 +1,26 @@
 #include "audio_mixer.h"
 
 #include <assert.h>
-#include <endian.h>
 #include <bmusb/bmusb.h>
-#include <stdio.h>
 #include <endian.h>
-#include <cmath>
-#ifdef __SSE__
+#include <math.h>
+#ifdef __SSE2__
 #include <immintrin.h>
 #endif
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <algorithm>
+#include <chrono>
+#include <cmath>
+#include <cstddef>
+#include <limits>
+#include <utility>
 
 #include "db.h"
 #include "flags.h"
+#include "state.pb.h"
 #include "timebase.h"
 
 using namespace bmusb;
@@ -161,37 +170,39 @@ AudioMixer::AudioMixer(unsigned num_cards)
          limiter(OUTPUT_FREQUENCY),
          correlation(OUTPUT_FREQUENCY)
 {
+       global_audio_mixer = this;
+
        for (unsigned bus_index = 0; bus_index < MAX_BUSES; ++bus_index) {
                locut[bus_index].init(FILTER_HPF, 2);
-               locut_enabled[bus_index] = global_flags.locut_enabled;
                eq[bus_index][EQ_BAND_BASS].init(FILTER_LOW_SHELF, 1);
                // Note: EQ_BAND_MID isn't used (see comments in apply_eq()).
                eq[bus_index][EQ_BAND_TREBLE].init(FILTER_HIGH_SHELF, 1);
-
-               gain_staging_db[bus_index] = global_flags.initial_gain_staging_db;
                compressor[bus_index].reset(new StereoCompressor(OUTPUT_FREQUENCY));
-               compressor_threshold_dbfs[bus_index] = ref_level_dbfs - 12.0f;  // -12 dB.
-               compressor_enabled[bus_index] = global_flags.compressor_enabled;
                level_compressor[bus_index].reset(new StereoCompressor(OUTPUT_FREQUENCY));
-               level_compressor_enabled[bus_index] = global_flags.gain_staging_auto;
+
+               set_bus_settings(bus_index, get_default_bus_settings());
        }
        set_limiter_enabled(global_flags.limiter_enabled);
        set_final_makeup_gain_auto(global_flags.final_makeup_gain_auto);
-
-       // Generate a very simple, default input mapping.
-       InputMapping::Bus input;
-       input.name = "Main";
-       input.device.type = InputSourceType::CAPTURE_CARD;
-       input.device.index = 0;
-       input.source_channel[0] = 0;
-       input.source_channel[1] = 1;
-
-       InputMapping new_input_mapping;
-       new_input_mapping.buses.push_back(input);
-       set_input_mapping(new_input_mapping);
-
-       // Look for ALSA cards.
-       available_alsa_cards = ALSAInput::enumerate_devices();
+       alsa_pool.init();
+
+       if (!global_flags.input_mapping_filename.empty()) {
+               current_mapping_mode = MappingMode::MULTICHANNEL;
+               InputMapping new_input_mapping;
+               if (!load_input_mapping_from_file(get_devices(),
+                                                 global_flags.input_mapping_filename,
+                                                 &new_input_mapping)) {
+                       fprintf(stderr, "Failed to load input mapping from '%s', exiting.\n",
+                               global_flags.input_mapping_filename.c_str());
+                       exit(1);
+               }
+               set_input_mapping(new_input_mapping);
+       } else {
+               set_simple_input(/*card_index=*/0);
+               if (global_flags.multichannel_mapping_mode) {
+                       current_mapping_mode = MappingMode::MULTICHANNEL;
+               }
+       }
 
        r128.init(2, OUTPUT_FREQUENCY);
        r128.integr_start();
@@ -201,17 +212,6 @@ AudioMixer::AudioMixer(unsigned num_cards)
        peak_resampler.setup(OUTPUT_FREQUENCY, OUTPUT_FREQUENCY * 4, /*num_channels=*/2, /*hlen=*/16, /*frel=*/1.0);
 }
 
-AudioMixer::~AudioMixer()
-{
-       for (unsigned card_index = 0; card_index < available_alsa_cards.size(); ++card_index) {
-               const AudioDevice &device = alsa_inputs[card_index];
-               if (device.alsa_device != nullptr) {
-                       device.alsa_device->stop_capture_thread();
-               }
-       }
-}
-
-
 void AudioMixer::reset_resampler(DeviceSpec device_spec)
 {
        lock_guard<timed_mutex> lock(audio_mutex);
@@ -232,25 +232,6 @@ void AudioMixer::reset_resampler_mutex_held(DeviceSpec device_spec)
        device->next_local_pts = 0;
 }
 
-void AudioMixer::reset_alsa_mutex_held(DeviceSpec device_spec)
-{
-       assert(device_spec.type == InputSourceType::ALSA_INPUT);
-       unsigned card_index = device_spec.index;
-       AudioDevice *device = find_audio_device(device_spec);
-
-       if (device->alsa_device != nullptr) {
-               device->alsa_device->stop_capture_thread();
-       }
-       if (device->interesting_channels.empty()) {
-               device->alsa_device.reset();
-       } else {
-               const ALSAInput::Device &alsa_dev = available_alsa_cards[card_index];
-               device->alsa_device.reset(new ALSAInput(alsa_dev.address.c_str(), OUTPUT_FREQUENCY, alsa_dev.num_channels, bind(&AudioMixer::add_audio, this, device_spec, _1, _2, _3, _4)));
-               device->capture_frequency = device->alsa_device->get_sample_rate();
-               device->alsa_device->start_capture_thread();
-       }
-}
-
 bool AudioMixer::add_audio(DeviceSpec device_spec, const uint8_t *data, unsigned num_samples, AudioFormat audio_format, int64_t frame_length)
 {
        AudioDevice *device = find_audio_device(device_spec);
@@ -324,6 +305,71 @@ 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::BusSettings AudioMixer::get_default_bus_settings()
+{
+       BusSettings settings;
+       settings.fader_volume_db = 0.0f;
+       settings.muted = false;
+       settings.locut_enabled = global_flags.locut_enabled;
+       for (unsigned band_index = 0; band_index < NUM_EQ_BANDS; ++band_index) {
+               settings.eq_level_db[band_index] = 0.0f;
+       }
+       settings.gain_staging_db = global_flags.initial_gain_staging_db;
+       settings.level_compressor_enabled = global_flags.gain_staging_auto;
+       settings.compressor_threshold_dbfs = ref_level_dbfs - 12.0f;  // -12 dB.
+       settings.compressor_enabled = global_flags.compressor_enabled;
+       return settings;
+}
+
+AudioMixer::BusSettings AudioMixer::get_bus_settings(unsigned bus_index) const
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       BusSettings settings;
+       settings.fader_volume_db = fader_volume_db[bus_index];
+       settings.muted = mute[bus_index];
+       settings.locut_enabled = locut_enabled[bus_index];
+       for (unsigned band_index = 0; band_index < NUM_EQ_BANDS; ++band_index) {
+               settings.eq_level_db[band_index] = eq_level_db[bus_index][band_index];
+       }
+       settings.gain_staging_db = gain_staging_db[bus_index];
+       settings.level_compressor_enabled = level_compressor_enabled[bus_index];
+       settings.compressor_threshold_dbfs = compressor_threshold_dbfs[bus_index];
+       settings.compressor_enabled = compressor_enabled[bus_index];
+       return settings;
+}
+
+void AudioMixer::set_bus_settings(unsigned bus_index, const AudioMixer::BusSettings &settings)
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       fader_volume_db[bus_index] = settings.fader_volume_db;
+       mute[bus_index] = settings.muted;
+       locut_enabled[bus_index] = settings.locut_enabled;
+       for (unsigned band_index = 0; band_index < NUM_EQ_BANDS; ++band_index) {
+               eq_level_db[bus_index][band_index] = settings.eq_level_db[band_index];
+       }
+       gain_staging_db[bus_index] = settings.gain_staging_db;
+       last_gain_staging_db[bus_index] = gain_staging_db[bus_index];
+       level_compressor_enabled[bus_index] = settings.level_compressor_enabled;
+       compressor_threshold_dbfs[bus_index] = settings.compressor_threshold_dbfs;
+       compressor_enabled[bus_index] = settings.compressor_enabled;
+}
+
 AudioMixer::AudioDevice *AudioMixer::find_audio_device(DeviceSpec device)
 {
        switch (device.type) {
@@ -366,7 +412,7 @@ void AudioMixer::find_sample_src_from_device(const map<DeviceSpec, vector<float>
 void AudioMixer::fill_audio_bus(const map<DeviceSpec, vector<float>> &samples_card, const InputMapping::Bus &bus, unsigned num_samples, float *output)
 {
        if (bus.device.type == InputSourceType::SILENCE) {
-               memset(output, 0, num_samples * sizeof(*output));
+               memset(output, 0, num_samples * 2 * sizeof(*output));
        } else {
                assert(bus.device.type == InputSourceType::CAPTURE_CARD ||
                       bus.device.type == InputSourceType::ALSA_INPUT);
@@ -384,6 +430,49 @@ void AudioMixer::fill_audio_bus(const map<DeviceSpec, vector<float>> &samples_ca
        }
 }
 
+vector<DeviceSpec> AudioMixer::get_active_devices() const
+{
+       vector<DeviceSpec> ret;
+       for (unsigned card_index = 0; card_index < MAX_VIDEO_CARDS; ++card_index) {
+               const DeviceSpec device_spec{InputSourceType::CAPTURE_CARD, card_index};
+               if (!find_audio_device(device_spec)->interesting_channels.empty()) {
+                       ret.push_back(device_spec);
+               }
+       }
+       for (unsigned card_index = 0; card_index < MAX_ALSA_CARDS; ++card_index) {
+               const DeviceSpec device_spec{InputSourceType::ALSA_INPUT, card_index};
+               if (!find_audio_device(device_spec)->interesting_channels.empty()) {
+                       ret.push_back(device_spec);
+               }
+       }
+       return ret;
+}
+
+namespace {
+
+void apply_gain(float db, float last_db, vector<float> *samples)
+{
+       if (fabs(db - last_db) < 1e-3) {
+               // Constant over this frame.
+               const float gain = from_db(db);
+               for (size_t i = 0; i < samples->size(); ++i) {
+                       (*samples)[i] *= gain;
+               }
+       } else {
+               // We need to do a fade.
+               unsigned num_samples = samples->size() / 2;
+               float gain = from_db(last_db);
+               const float gain_inc = pow(from_db(db - last_db), 1.0 / num_samples);
+               for (size_t i = 0; i < num_samples; ++i) {
+                       (*samples)[i * 2 + 0] *= gain;
+                       (*samples)[i * 2 + 1] *= gain;
+                       gain *= gain_inc;
+               }
+       }
+}
+
+}  // namespace
+
 vector<float> AudioMixer::get_output(double pts, unsigned num_samples, ResamplingQueue::RateAdjustmentPolicy rate_adjustment_policy)
 {
        map<DeviceSpec, vector<float>> samples_card;
@@ -392,14 +481,12 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
        lock_guard<timed_mutex> lock(audio_mutex);
 
        // Pick out all the interesting channels from all the cards.
-       // TODO: If the card has been hotswapped, the number of channels
-       // might have changed; if so, we need to do some sort of remapping
-       // to silence.
-       for (const auto &spec_and_info : get_devices_mutex_held()) {
-               const DeviceSpec &device_spec = spec_and_info.first;
+       for (const DeviceSpec &device_spec : get_active_devices()) {
                AudioDevice *device = find_audio_device(device_spec);
-               if (!device->interesting_channels.empty()) {
-                       samples_card[device_spec].resize(num_samples * device->interesting_channels.size());
+               samples_card[device_spec].resize(num_samples * device->interesting_channels.size());
+               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],
@@ -434,11 +521,11 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
                                gain_staging_db[bus_index] = to_db(level_compressor[bus_index]->get_attenuation() * makeup_gain);
                        } else {
                                // Just apply the gain we already had.
-                               float g = from_db(gain_staging_db[bus_index]);
-                               for (size_t i = 0; i < samples_bus.size(); ++i) {
-                                       samples_bus[i] *= g;
-                               }
+                               float db = gain_staging_db[bus_index];
+                               float last_db = last_gain_staging_db[bus_index];
+                               apply_gain(db, last_db, &samples_bus);
                        }
+                       last_gain_staging_db[bus_index] = gain_staging_db[bus_index];
 
 #if 0
                        printf("level=%f (%+5.2f dBFS) attenuation=%f (%+5.2f dB) end_result=%+5.2f dB\n",
@@ -496,13 +583,12 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
        // (half-time of 30 seconds).
        double target_loudness_factor, alpha;
        double loudness_lu = r128.loudness_M() - ref_level_lufs;
-       double current_makeup_lu = to_db(final_makeup_gain);
        target_loudness_factor = final_makeup_gain * from_db(-loudness_lu);
 
-       // If we're outside +/- 5 LU uncorrected, we don't count it as
+       // If we're outside +/- 5 LU (after correction), we don't count it as
        // a normal signal (probably silence) and don't change the
        // correction factor; just apply what we already have.
-       if (fabs(loudness_lu - current_makeup_lu) >= 5.0 || !final_makeup_gain_auto) {
+       if (fabs(loudness_lu) >= 5.0 || !final_makeup_gain_auto) {
                alpha = 0.0;
        } else {
                // Formula adapted from
@@ -528,6 +614,36 @@ vector<float> AudioMixer::get_output(double pts, unsigned num_samples, Resamplin
        return samples_out;
 }
 
+namespace {
+
+void apply_filter_fade(StereoFilter *filter, float *data, unsigned num_samples, float cutoff_hz, float db, float last_db)
+{
+       // A granularity of 32 samples is an okay tradeoff between speed and
+       // smoothness; recalculating the filters is pretty expensive, so it's
+       // good that we don't do this all the time.
+       static constexpr unsigned filter_granularity_samples = 32;
+
+       const float cutoff_linear = cutoff_hz * 2.0 * M_PI / OUTPUT_FREQUENCY;
+       if (fabs(db - last_db) < 1e-3) {
+               // Constant over this frame.
+               if (fabs(db) > 0.01f) {
+                       filter->render(data, num_samples, cutoff_linear, 0.5f, db / 40.0f);
+               }
+       } else {
+               // We need to do a fade. (Rounding up avoids division by zero.)
+               unsigned num_blocks = (num_samples + filter_granularity_samples - 1) / filter_granularity_samples;
+               const float inc_db_norm = (db - last_db) / 40.0f / num_blocks;
+               float db_norm = db / 40.0f;
+               for (size_t i = 0; i < num_samples; i += filter_granularity_samples) {
+                       size_t samples_this_block = std::min<size_t>(num_samples - i, filter_granularity_samples);
+                       filter->render(data + i * 2, samples_this_block, cutoff_linear, 0.5f, db_norm);
+                       db_norm += inc_db_norm;
+               }
+       }
+}
+
+}  // namespace
+
 void AudioMixer::apply_eq(unsigned bus_index, vector<float> *samples_bus)
 {
        constexpr float bass_freq_hz = 200.0f;
@@ -546,24 +662,28 @@ void AudioMixer::apply_eq(unsigned bus_index, vector<float> *samples_bus)
        // set the mid-level filter, and then offset the low and high bands
        // from that if we need to. (We could perhaps have folded the gain into
        // the next part, but it's so cheap that the trouble isn't worth it.)
-       if (fabs(eq_level_db[bus_index][EQ_BAND_MID]) > 0.01f) {
-               float g = from_db(eq_level_db[bus_index][EQ_BAND_MID]);
-               for (size_t i = 0; i < samples_bus->size(); ++i) {
-                       (*samples_bus)[i] *= g;
-               }
-       }
+       //
+       // If any part of the EQ has changed appreciably since last frame,
+       // we fade smoothly during the course of this frame.
+       const float bass_db = eq_level_db[bus_index][EQ_BAND_BASS];
+       const float mid_db = eq_level_db[bus_index][EQ_BAND_MID];
+       const float treble_db = eq_level_db[bus_index][EQ_BAND_TREBLE];
 
-       float bass_adj_db = eq_level_db[bus_index][EQ_BAND_BASS] - eq_level_db[bus_index][EQ_BAND_MID];
-       if (fabs(bass_adj_db) > 0.01f) {
-               eq[bus_index][EQ_BAND_BASS].render(samples_bus->data(), samples_bus->size() / 2,
-                       bass_freq_hz * 2.0 * M_PI / OUTPUT_FREQUENCY, 0.5f, bass_adj_db / 40.0f);
-       }
+       const float last_bass_db = last_eq_level_db[bus_index][EQ_BAND_BASS];
+       const float last_mid_db = last_eq_level_db[bus_index][EQ_BAND_MID];
+       const float last_treble_db = last_eq_level_db[bus_index][EQ_BAND_TREBLE];
 
-       float treble_adj_db = eq_level_db[bus_index][EQ_BAND_TREBLE] - eq_level_db[bus_index][EQ_BAND_MID];
-       if (fabs(treble_adj_db) > 0.01f) {
-               eq[bus_index][EQ_BAND_TREBLE].render(samples_bus->data(), samples_bus->size() / 2,
-                       treble_freq_hz * 2.0 * M_PI / OUTPUT_FREQUENCY, 0.5f, treble_adj_db / 40.0f);
-       }
+       assert(samples_bus->size() % 2 == 0);
+       const unsigned num_samples = samples_bus->size() / 2;
+
+       apply_gain(mid_db, last_mid_db, samples_bus);
+
+       apply_filter_fade(&eq[bus_index][EQ_BAND_BASS], samples_bus->data(), num_samples, bass_freq_hz, bass_db - mid_db, last_bass_db - last_mid_db);
+       apply_filter_fade(&eq[bus_index][EQ_BAND_TREBLE], samples_bus->data(), num_samples, treble_freq_hz, treble_db - mid_db, last_treble_db - last_mid_db);
+
+       last_eq_level_db[bus_index][EQ_BAND_BASS] = bass_db;
+       last_eq_level_db[bus_index][EQ_BAND_MID] = mid_db;
+       last_eq_level_db[bus_index][EQ_BAND_TREBLE] = treble_db;
 }
 
 void AudioMixer::add_bus_to_master(unsigned bus_index, const vector<float> &samples_bus, vector<float> *samples_out)
@@ -571,13 +691,14 @@ void AudioMixer::add_bus_to_master(unsigned bus_index, const vector<float> &samp
        assert(samples_bus.size() == samples_out->size());
        assert(samples_bus.size() % 2 == 0);
        unsigned num_samples = samples_bus.size() / 2;
-       if (fabs(fader_volume_db[bus_index] - last_fader_volume_db[bus_index]) > 1e-3) {
+       const float new_volume_db = mute[bus_index] ? -90.0f : fader_volume_db[bus_index].load();
+       if (fabs(new_volume_db - last_fader_volume_db[bus_index]) > 1e-3) {
                // The volume has changed; do a fade over the course of this frame.
                // (We might have some numerical issues here, but it seems to sound OK.)
                // For the purpose of fading here, the silence floor is set to -90 dB
                // (the fader only goes to -84).
                float old_volume = from_db(max<float>(last_fader_volume_db[bus_index], -90.0f));
-               float volume = from_db(max<float>(fader_volume_db[bus_index], -90.0f));
+               float volume = from_db(max<float>(new_volume_db, -90.0f));
 
                float volume_inc = pow(volume / old_volume, 1.0 / num_samples);
                volume = old_volume;
@@ -594,8 +715,8 @@ void AudioMixer::add_bus_to_master(unsigned bus_index, const vector<float> &samp
                                volume *= volume_inc;
                        }
                }
-       } else {
-               float volume = from_db(fader_volume_db[bus_index]);
+       } else if (new_volume_db > -90.0f) {
+               float volume = from_db(new_volume_db);
                if (bus_index == 0) {
                        for (unsigned i = 0; i < num_samples; ++i) {
                                (*samples_out)[i * 2 + 0] = samples_bus[i * 2 + 0] * volume;
@@ -609,13 +730,13 @@ void AudioMixer::add_bus_to_master(unsigned bus_index, const vector<float> &samp
                }
        }
 
-       last_fader_volume_db[bus_index] = fader_volume_db[bus_index];
+       last_fader_volume_db[bus_index] = new_volume_db;
 }
 
 void AudioMixer::measure_bus_levels(unsigned bus_index, const vector<float> &left, const vector<float> &right)
 {
        assert(left.size() == right.size());
-       const float volume = from_db(fader_volume_db[bus_index]);
+       const float volume = mute[bus_index] ? 0.0f : from_db(fader_volume_db[bus_index]);
        const float peak_levels[2] = {
                find_peak(left.data(), left.size()) * volume,
                find_peak(right.data(), right.size()) * volume
@@ -730,46 +851,106 @@ void AudioMixer::send_audio_level_callback()
                correlation.get_correlation());
 }
 
-map<DeviceSpec, DeviceInfo> AudioMixer::get_devices() const
+map<DeviceSpec, DeviceInfo> AudioMixer::get_devices()
 {
        lock_guard<timed_mutex> lock(audio_mutex);
-       return get_devices_mutex_held();
-}
 
-map<DeviceSpec, DeviceInfo> AudioMixer::get_devices_mutex_held() const
-{
        map<DeviceSpec, DeviceInfo> devices;
        for (unsigned card_index = 0; card_index < num_cards; ++card_index) {
                const DeviceSpec spec{ InputSourceType::CAPTURE_CARD, card_index };
                const AudioDevice *device = &video_cards[card_index];
                DeviceInfo info;
-               info.name = device->name;
-               info.num_channels = 8;  // FIXME: This is wrong for fake cards.
+               info.display_name = device->display_name;
+               info.num_channels = 8;
                devices.insert(make_pair(spec, info));
        }
-       for (unsigned card_index = 0; card_index < available_alsa_cards.size(); ++card_index) {
+       vector<ALSAPool::Device> available_alsa_devices = alsa_pool.get_devices();
+       for (unsigned card_index = 0; card_index < available_alsa_devices.size(); ++card_index) {
                const DeviceSpec spec{ InputSourceType::ALSA_INPUT, card_index };
-               const ALSAInput::Device &device = available_alsa_cards[card_index];
+               const ALSAPool::Device &device = available_alsa_devices[card_index];
                DeviceInfo info;
-               info.name = device.name + " (" + device.info + ")";
+               info.display_name = device.display_name();
                info.num_channels = device.num_channels;
+               info.alsa_name = device.name;
+               info.alsa_info = device.info;
+               info.alsa_address = device.address;
                devices.insert(make_pair(spec, info));
        }
        return devices;
 }
 
-void AudioMixer::set_name(DeviceSpec device_spec, const string &name)
+void AudioMixer::set_display_name(DeviceSpec device_spec, const string &name)
 {
        AudioDevice *device = find_audio_device(device_spec);
 
        lock_guard<timed_mutex> lock(audio_mutex);
-       device->name = name;
+       device->display_name = name;
+}
+
+void AudioMixer::serialize_device(DeviceSpec device_spec, DeviceSpecProto *device_spec_proto)
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       switch (device_spec.type) {
+               case InputSourceType::SILENCE:
+                       device_spec_proto->set_type(DeviceSpecProto::SILENCE);
+                       break;
+               case InputSourceType::CAPTURE_CARD:
+                       device_spec_proto->set_type(DeviceSpecProto::CAPTURE_CARD);
+                       device_spec_proto->set_index(device_spec.index);
+                       device_spec_proto->set_display_name(video_cards[device_spec.index].display_name);
+                       break;
+               case InputSourceType::ALSA_INPUT:
+                       alsa_pool.serialize_device(device_spec.index, device_spec_proto);
+                       break;
+       }
+}
+
+void AudioMixer::set_simple_input(unsigned card_index)
+{
+       InputMapping new_input_mapping;
+       InputMapping::Bus input;
+       input.name = "Main";
+       input.device.type = InputSourceType::CAPTURE_CARD;
+       input.device.index = card_index;
+       input.source_channel[0] = 0;
+       input.source_channel[1] = 1;
+
+       new_input_mapping.buses.push_back(input);
+
+       lock_guard<timed_mutex> lock(audio_mutex);
+       current_mapping_mode = MappingMode::SIMPLE;
+       set_input_mapping_lock_held(new_input_mapping);
+       fader_volume_db[0] = 0.0f;
+}
+
+unsigned AudioMixer::get_simple_input() const
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       if (input_mapping.buses.size() == 1 &&
+           input_mapping.buses[0].device.type == InputSourceType::CAPTURE_CARD &&
+           input_mapping.buses[0].source_channel[0] == 0 &&
+           input_mapping.buses[0].source_channel[1] == 1) {
+               return input_mapping.buses[0].device.index;
+       } else {
+               return numeric_limits<unsigned>::max();
+       }
 }
 
 void AudioMixer::set_input_mapping(const InputMapping &new_input_mapping)
 {
        lock_guard<timed_mutex> lock(audio_mutex);
+       set_input_mapping_lock_held(new_input_mapping);
+       current_mapping_mode = MappingMode::MULTICHANNEL;
+}
 
+AudioMixer::MappingMode AudioMixer::get_mapping_mode() const
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       return current_mapping_mode;
+}
+
+void AudioMixer::set_input_mapping_lock_held(const InputMapping &new_input_mapping)
+{
        map<DeviceSpec, set<unsigned>> interesting_channels;
        for (const InputMapping::Bus &bus : new_input_mapping.buses) {
                if (bus.device.type == InputSourceType::CAPTURE_CARD ||
@@ -783,14 +964,25 @@ void AudioMixer::set_input_mapping(const InputMapping &new_input_mapping)
        }
 
        // Reset resamplers for all cards that don't have the exact same state as before.
-       for (const auto &spec_and_info : get_devices_mutex_held()) {
-               const DeviceSpec &device_spec = spec_and_info.first;
+       for (unsigned card_index = 0; card_index < MAX_VIDEO_CARDS; ++card_index) {
+               const DeviceSpec device_spec{InputSourceType::CAPTURE_CARD, card_index};
                AudioDevice *device = find_audio_device(device_spec);
                if (device->interesting_channels != interesting_channels[device_spec]) {
                        device->interesting_channels = interesting_channels[device_spec];
-                       if (device_spec.type == InputSourceType::ALSA_INPUT) {
-                               reset_alsa_mutex_held(device_spec);
-                       }
+                       reset_resampler_mutex_held(device_spec);
+               }
+       }
+       for (unsigned card_index = 0; card_index < MAX_ALSA_CARDS; ++card_index) {
+               const DeviceSpec device_spec{InputSourceType::ALSA_INPUT, card_index};
+               AudioDevice *device = find_audio_device(device_spec);
+               if (interesting_channels[device_spec].empty()) {
+                       alsa_pool.release_device(card_index);
+               } else {
+                       alsa_pool.hold_device(card_index);
+               }
+               if (device->interesting_channels != interesting_channels[device_spec]) {
+                       device->interesting_channels = interesting_channels[device_spec];
+                       alsa_pool.reset_device(device_spec.index);
                        reset_resampler_mutex_held(device_spec);
                }
        }
@@ -804,6 +996,12 @@ InputMapping AudioMixer::get_input_mapping() const
        return input_mapping;
 }
 
+unsigned AudioMixer::num_buses() const
+{
+       lock_guard<timed_mutex> lock(audio_mutex);
+       return input_mapping.buses.size();
+}
+
 void AudioMixer::reset_peak(unsigned bus_index)
 {
        lock_guard<timed_mutex> lock(audio_mutex);