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>

1 files changed, 3 insertions, 0 deletions

diff --git a/src/modules/bluetooth/a2dp-codec-api.h b/src/modules/bluetooth/a2dp-codec-api.h
index a3123f4ca..61c66de88 100644
--- a/src/modules/bluetooth/a2dp-codec-api.h
+++ b/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);