Add some ALSA device enumeration code.

diff --git a/alsa_input.cpp b/alsa_input.cpp
index fc710a3cb3e7ea186e0ac2cef36065601e21ea1e..22daf760b026cb8c27cd8b4604ab41488667f345 100644 (file)
--- a/alsa_input.cpp
+++ b/alsa_input.cpp
@@ -76,7 +76,6 @@ ALSAInput::ALSAInput(const char *device, unsigned sample_rate, unsigned num_chan
 
        die_on_error("snd_pcm_nonblock()", snd_pcm_nonblock(pcm_handle, 1));
        die_on_error("snd_pcm_prepare()", snd_pcm_prepare(pcm_handle));
-
 }
 
 ALSAInput::~ALSAInput()
@@ -144,3 +143,66 @@ void ALSAInput::die_on_error(const char *func_name, int err)
        }
 }
 
+vector<ALSAInput::Device> ALSAInput::enumerate_devices()
+{
+       vector<Device> ret;
+
+       // Enumerate all cards.
+       for (int card_index = -1; snd_card_next(&card_index) == 0 && card_index >= 0; ) {
+               char address[256];
+               snprintf(address, sizeof(address), "hw:%d", card_index);
+
+               snd_ctl_t *ctl;
+               int err = snd_ctl_open(&ctl, address, 0);
+               if (err < 0) {
+                       printf("%s: %s\n", address, snd_strerror(err));
+                       continue;
+               }
+               snd_ctl_card_info_t *card_info;
+               snd_ctl_card_info_alloca(&card_info);
+               snd_ctl_card_info(ctl, card_info);
+
+               string card_name = snd_ctl_card_info_get_name(card_info);
+
+               // Enumerate all devices on this card.
+               for (int dev_index = -1; snd_ctl_pcm_next_device(ctl, &dev_index) == 0 && dev_index >= 0; ) {
+                       snd_pcm_info_t *pcm_info;
+                       snd_pcm_info_alloca(&pcm_info);
+                       snd_pcm_info_set_device(pcm_info, dev_index);
+                       snd_pcm_info_set_subdevice(pcm_info, 0);
+                       snd_pcm_info_set_stream(pcm_info, SND_PCM_STREAM_CAPTURE);
+                       if (snd_ctl_pcm_info(ctl, pcm_info) < 0) {
+                               // Not available for capture.
+                               continue;
+                       }
+
+                       snprintf(address, sizeof(address), "hw:%d,%d", card_index, dev_index);
+
+                       // Find all channel maps for this device, and pick out the one
+                       // with the most channels.
+                       snd_pcm_chmap_query_t **cmaps = snd_pcm_query_chmaps_from_hw(card_index, dev_index, 0, SND_PCM_STREAM_CAPTURE);
+                       unsigned num_channels = 0;
+                       for (snd_pcm_chmap_query_t **ptr = cmaps; *ptr; ++ptr) {
+                               num_channels = max(num_channels, (*ptr)->map.channels);
+                       }
+
+                       snd_pcm_free_chmaps(cmaps);
+
+                       if (num_channels == 0) {
+                               printf("%s: No channel maps with channels\n", address);
+                               continue;
+                       }
+
+                       Device dev;
+                       dev.address = address;
+                       dev.name = card_name;
+                       dev.info = snd_pcm_info_get_name(pcm_info);
+                       dev.num_channels = num_channels;
+
+                       ret.push_back(dev);
+               }
+               snd_ctl_close(ctl);
+       }
+
+       return ret;
+}

diff --git a/alsa_input.h b/alsa_input.h
index 724b64011749f01bc554cb720e3c095473113c3c..d485a3b74e18b1ce823c5dbf9d5ea7df08ad1ce2 100644 (file)
--- a/alsa_input.h
+++ b/alsa_input.h
@@ -34,6 +34,14 @@ public:
        void start_capture_thread();
        void stop_capture_thread();
 
+       // TODO: Worry about hotplug.
+       struct Device {
+               std::string address;  // E.g. “hw:0,0”.
+               std::string name, info;
+               unsigned num_channels;
+       };
+       static std::vector<Device> enumerate_devices();
+
 private:
        void capture_thread_func();
        int64_t frames_to_pts(uint64_t n) const;