Android framework defined two hardware interfaces for operating audio output devices, they are audio_hw_device_t and audio_stream_out_t, AudioFlinger is the only user of these interfaces. Bluedroid implemented these two interface in external/bluetooth/bluedroid/audio_a2dp_hw/audio_a2dp_hw.c, AudioFlinger can output audio sample to a connected A2DP sink device if this implementation has been registered to Android.

In Bluedroid’s A2DP hardware implementation, it will use two sockets to communicate with A2DP server.

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