bluetooth: Introduce a can_be_supported API for A2DP codecs

This API internally checks if a requested codec can be supported on the
system. This is especially required for codecs supported via GStreamer
where the availability of a plugin decides if the said codec can be
supported.

This will be used to prevent registration of a codec which the remote
endpoint device might be able to support, but, PulseAudio can't as the
codec is not available on the system due to the absence of a plugin.
We can also prevent listing or switching to an unavailable codec.

Note that the codec negotiation happens with the bluez stack even before
a device is connected. Because of this, we need to make sure that gst_init
is called before checking for the availability of a plugin. Since
module-bluez5-device gets loaded only after a connection to the device
has been established, doing the gst_init in that or one of the bluetooth
modules is not feasible.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/440>

src/modules/bluetooth/a2dp-codec-api.h

@@ -48,6 +48,9 @@ typedef struct pa_a2dp_codec {
     /* True if codec is bi-directional and supports backchannel */
     bool support_backchannel;
 
+    /* Returns true if the codec can be supported on the system */
+    bool (*can_be_supported)(void);
+
     /* Returns true if codec accepts capabilities, for_encoding is true when
      * capabilities are used for encoding */
     bool (*can_accept_capabilities)(const uint8_t *capabilities_buffer, uint8_t capabilities_size, bool for_encoding);

src/modules/bluetooth/a2dp-codec-aptx-gst.c

@@ -33,6 +33,28 @@
 #include "a2dp-codec-gst.h"
 #include "rtp.h"
 
+static bool can_be_supported(void) {
+    GstElementFactory *element_factory;
+
+    element_factory = gst_element_factory_find("openaptxenc");
+    if (element_factory == NULL) {
+        pa_log_info("aptX encoder not found");
+        return false;
+    }
+
+    gst_object_unref(element_factory);
+
+    element_factory = gst_element_factory_find("openaptxdec");
+    if (element_factory == NULL) {
+        pa_log_info("aptX decoder not found");
+        return false;
+    }
+
+    gst_object_unref(element_factory);
+
+    return true;
+}
+
 static bool can_accept_capabilities_common(const a2dp_aptx_t *capabilities, uint32_t vendor_id, uint16_t codec_id) {
     if (A2DP_GET_VENDOR_ID(capabilities->info) != vendor_id || A2DP_GET_CODEC_ID(capabilities->info) != codec_id)
         return false;
@@ -359,6 +381,7 @@ const pa_a2dp_codec pa_a2dp_codec_aptx = {
     .description = "aptX",
     .id = { A2DP_CODEC_VENDOR, APTX_VENDOR_ID, APTX_CODEC_ID },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities,
     .choose_remote_endpoint = choose_remote_endpoint,
     .fill_capabilities = fill_capabilities,
@@ -379,6 +402,7 @@ const pa_a2dp_codec pa_a2dp_codec_aptx_hd = {
     .description = "aptX HD",
     .id = { A2DP_CODEC_VENDOR, APTX_HD_VENDOR_ID, APTX_HD_CODEC_ID },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities_hd,
     .choose_remote_endpoint = choose_remote_endpoint_hd,
     .fill_capabilities = fill_capabilities_hd,

src/modules/bluetooth/a2dp-codec-gst.c

@@ -575,15 +575,8 @@ fail:
 
 void *gst_codec_init(enum a2dp_codec_type codec_type, const uint8_t *config_buffer, uint8_t config_size, pa_sample_spec *ss) {
     struct gst_info *info = NULL;
-    GError *error = NULL;
     bool ret;
 
-    if (!gst_init_check(NULL, NULL, &error)) {
-        pa_log_error("Could not initialise GStreamer: %s", error->message);
-        g_error_free(error);
-        goto fail;
-    }
-
     info = pa_xnew0(struct gst_info, 1);
     pa_assert(info);
 

src/modules/bluetooth/a2dp-codec-ldac-gst.c

@@ -33,6 +33,20 @@
 #include "a2dp-codec-gst.h"
 #include "rtp.h"
 
+static bool can_be_supported(void) {
+    GstElementFactory *element_factory;
+
+    element_factory = gst_element_factory_find("ldacenc");
+    if (element_factory == NULL) {
+        pa_log_info("LDAC encoder not found");
+        return false;
+    }
+
+    gst_object_unref(element_factory);
+
+    return true;
+}
+
 static bool can_accept_capabilities_common(const a2dp_ldac_t *capabilities, uint32_t vendor_id, uint16_t codec_id) {
     if (A2DP_GET_VENDOR_ID(capabilities->info) != vendor_id || A2DP_GET_CODEC_ID(capabilities->info) != codec_id)
         return false;
@@ -276,6 +290,7 @@ const pa_a2dp_codec pa_a2dp_codec_ldac_eqmid_hq = {
     .description = "LDAC (High Quality)",
     .id = { A2DP_CODEC_VENDOR, LDAC_VENDOR_ID, LDAC_CODEC_ID },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities,
     .choose_remote_endpoint = choose_remote_endpoint,
     .fill_capabilities = fill_capabilities,
@@ -295,6 +310,7 @@ const pa_a2dp_codec pa_a2dp_codec_ldac_eqmid_sq = {
     .description = "LDAC (Standard Quality)",
     .id = { A2DP_CODEC_VENDOR, LDAC_VENDOR_ID, LDAC_CODEC_ID },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities,
     .choose_remote_endpoint = choose_remote_endpoint,
     .fill_capabilities = fill_capabilities,
@@ -314,6 +330,7 @@ const pa_a2dp_codec pa_a2dp_codec_ldac_eqmid_mq = {
     .description = "LDAC (Mobile Quality)",
     .id = { A2DP_CODEC_VENDOR, LDAC_VENDOR_ID, LDAC_CODEC_ID },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities,
     .choose_remote_endpoint = choose_remote_endpoint,
     .fill_capabilities = fill_capabilities,

src/modules/bluetooth/a2dp-codec-sbc.c

@@ -53,6 +53,10 @@ struct sbc_info {
     uint8_t max_bitpool;
 };
 
+static bool can_be_supported(void) {
+    return true;
+}
+
 static bool can_accept_capabilities(const uint8_t *capabilities_buffer, uint8_t capabilities_size, bool for_encoding) {
     const a2dp_sbc_t *capabilities = (const a2dp_sbc_t *) capabilities_buffer;
 
@@ -666,6 +670,7 @@ const pa_a2dp_codec pa_a2dp_codec_sbc = {
     .description = "SBC",
     .id = { A2DP_CODEC_SBC, 0, 0 },
     .support_backchannel = false,
+    .can_be_supported = can_be_supported,
     .can_accept_capabilities = can_accept_capabilities,
     .choose_remote_endpoint = choose_remote_endpoint,
     .fill_capabilities = fill_capabilities,

src/modules/bluetooth/a2dp-codec-util.c

@@ -23,6 +23,9 @@
 
 #include <pulsecore/core.h>
 #include <pulsecore/core-util.h>
+#if defined(HAVE_GSTAPTX) || defined(HAVE_GSTLDAC)
+#include <gst/gst.h>
+#endif
 
 #include "a2dp-codec-util.h"
 
@@ -72,3 +75,16 @@ const pa_a2dp_codec *pa_bluetooth_get_a2dp_codec(const char *name) {
 
     return NULL;
 }
+
+void pa_bluetooth_a2dp_codec_gst_init(void) {
+#if defined(HAVE_GSTAPTX) || defined(HAVE_GSTLDAC)
+    GError *error = NULL;
+
+    if (!gst_init_check(NULL, NULL, &error)) {
+        pa_log_error("Could not initialise GStreamer: %s", error->message);
+        g_error_free(error);
+        return;
+    }
+    pa_log_info("GStreamer initialisation done");
+#endif
+}

src/modules/bluetooth/a2dp-codec-util.h

@@ -31,4 +31,7 @@ const pa_a2dp_codec *pa_bluetooth_a2dp_codec_iter(unsigned int i);
 /* Get codec by name */
 const pa_a2dp_codec *pa_bluetooth_get_a2dp_codec(const char *name);
 
+/* Initialise GStreamer */
+void pa_bluetooth_a2dp_codec_gst_init(void);
+
 #endif

src/modules/bluetooth/bluez5-util.c

@@ -2150,6 +2150,7 @@ pa_bluetooth_discovery* pa_bluetooth_discovery_get(pa_core *c, int headset_backe
     const pa_a2dp_codec *a2dp_codec;
     char *endpoint;
 
+    pa_bluetooth_a2dp_codec_gst_init();
     y = pa_xnew0(pa_bluetooth_discovery, 1);
     PA_REFCNT_INIT(y);
     y->core = c;