bluetooth: Modular API for A2DP codecs

This patch introduce new modular API for bluetooth A2DP codecs. Its
benefits are:

* bluez5-util and module-bluez5-device does not contain any codec specific
  code, they are codec independent.

* For adding new A2DP codec it is needed just to adjust one table in
  a2dp-codec-util.c file. All codec specific functions are in separate
  codec file.

* Support for backchannel (microphone voice). Some A2DP codecs (like
  FastStream or aptX Low Latency) are bi-directional and can be used for
  both music playback and audio call.

* Support for more configurations per codec. This allows to implement low
  quality mode of some codec together with high quality.

Current SBC codec implementation was moved from bluez5-util and
module-bluez5-device to its own file and converted to this new A2DP API.

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

@@ -0,0 +1,95 @@
+#ifndef fooa2dpcodechfoo
+#define fooa2dpcodechfoo
+
+/***
+  This file is part of PulseAudio.
+
+  Copyright 2018-2019 Pali Rohár <pali.rohar@gmail.com>
+
+  PulseAudio is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Lesser General Public License as
+  published by the Free Software Foundation; either version 2.1 of the
+  License, or (at your option) any later version.
+
+  PulseAudio is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+  General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with PulseAudio; if not, see <http://www.gnu.org/licenses/>.
+***/
+
+#include <pulsecore/core.h>
+
+#define MAX_A2DP_CAPS_SIZE 254
+
+typedef struct pa_a2dp_codec_capabilities {
+    uint8_t size;
+    uint8_t buffer[]; /* max size is 254 bytes */
+} pa_a2dp_codec_capabilities;
+
+typedef struct pa_a2dp_codec_id {
+    uint8_t codec_id;
+    uint32_t vendor_id;
+    uint16_t vendor_codec_id;
+} pa_a2dp_codec_id;
+
+typedef struct pa_a2dp_codec {
+    /* Unique name of the codec, lowercase and without whitespaces, used for
+     * constructing identifier, D-Bus paths, ... */
+    const char *name;
+    /* Human readable codec description */
+    const char *description;
+
+    /* A2DP codec id */
+    pa_a2dp_codec_id id;
+
+    /* True if codec is bi-directional and supports backchannel */
+    bool support_backchannel;
+
+    /* 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);
+    /* Choose remote endpoint based on capabilities from hash map
+     * (const char *endpoint -> const pa_a2dp_codec_capabilities *capability)
+     * and returns corresponding endpoint key (or NULL when there is no valid),
+     * for_encoder is true when capabilities hash map is used for encoding */
+    const char *(*choose_remote_endpoint)(const pa_hashmap *capabilities_hashmap, const pa_sample_spec *default_sample_spec, bool for_encoding);
+    /* Fill codec capabilities, returns size of filled buffer */
+    uint8_t (*fill_capabilities)(uint8_t capabilities_buffer[MAX_A2DP_CAPS_SIZE]);
+    /* Validate codec configuration, returns true on success */
+    bool (*is_configuration_valid)(const uint8_t *config_buffer, uint8_t config_size);
+    /* Fill preferred codec configuration, returns size of filled buffer or 0 on failure */
+    uint8_t (*fill_preferred_configuration)(const pa_sample_spec *default_sample_spec, const uint8_t *capabilities_buffer, uint8_t capabilities_size, uint8_t config_buffer[MAX_A2DP_CAPS_SIZE]);
+
+    /* Initialize codec, returns codec info data and set sample_spec,
+     * for_encoding is true when codec_info is used for encoding,
+     * for_backchannel is true when codec_info is used for backchannel */
+    void *(*init)(bool for_encoding, bool for_backchannel, const uint8_t *config_buffer, uint8_t config_size, pa_sample_spec *sample_spec);
+    /* Deinitialize and release codec info data in codec_info */
+    void (*deinit)(void *codec_info);
+    /* Reset internal state of codec info data in codec_info */
+    void (*reset)(void *codec_info);
+
+    /* Get read block size for codec */
+    size_t (*get_read_block_size)(void *codec_info, size_t read_link_mtu);
+    /* Get write block size for codec */
+    size_t (*get_write_block_size)(void *codec_info, size_t write_link_mtu);
+
+    /* Reduce encoder bitrate for codec, returns new write block size or zero
+     * if not changed, called when socket is not accepting encoded data fast
+     * enough */
+    size_t (*reduce_encoder_bitrate)(void *codec_info, size_t write_link_mtu);
+
+    /* Encode input_buffer of input_size to output_buffer of output_size,
+     * returns size of filled ouput_buffer and set processed to size of
+     * processed input_buffer */
+    size_t (*encode_buffer)(void *codec_info, uint32_t timestamp, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed);
+    /* Decode input_buffer of input_size to output_buffer of output_size,
+     * returns size of filled ouput_buffer and set processed to size of
+     * processed input_buffer */
+    size_t (*decode_buffer)(void *codec_info, const uint8_t *input_buffer, size_t input_size, uint8_t *output_buffer, size_t output_size, size_t *processed);
+} pa_a2dp_codec;
+
+#endif