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diff --git a/audio/audio_aec.h b/audio/audio_aec.h
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+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/*
+ * Definitions and interface related to HAL implementations of Acoustic Echo Canceller (AEC).
+ *
+ * AEC cleans the microphone signal by removing from it audio data corresponding to loudspeaker
+ * playback. Note that this process can be nonlinear.
+ *
+ */
+
+#ifndef _AUDIO_AEC_H_
+#define _AUDIO_AEC_H_
+
+#include <stdint.h>
+#include <pthread.h>
+#include <sys/time.h>
+#include <hardware/audio.h>
+#include <audio_utils/resampler.h>
+#include "audio_hw.h"
+#include "fifo_wrapper.h"
+
+struct aec_t {
+    pthread_mutex_t lock;
+    size_t num_reference_channels;
+    bool mic_initialized;
+    int32_t *mic_buf;
+    size_t mic_num_channels;
+    size_t mic_buf_size_bytes;
+    size_t mic_frame_size_bytes;
+    uint32_t mic_sampling_rate;
+    struct aec_info last_mic_info;
+    bool spk_initialized;
+    int32_t *spk_buf;
+    size_t spk_num_channels;
+    size_t spk_buf_size_bytes;
+    size_t spk_frame_size_bytes;
+    uint32_t spk_sampling_rate;
+    struct aec_info last_spk_info;
+    int16_t *spk_buf_playback_format;
+    int16_t *spk_buf_resampler_out;
+    void *spk_fifo;
+    void *ts_fifo;
+    ssize_t read_write_diff_bytes;
+    struct resampler_itfe *spk_resampler;
+    bool spk_running;
+    bool prev_spk_running;
+};
+
+/* Initialize AEC object.
+ * This must be called when the audio device is opened.
+ * ALSA device mutex must be held before calling this API.
+ * Returns -EINVAL if AEC object fails to initialize, else returns 0. */
+int init_aec (int sampling_rate, int num_reference_channels,
+                int num_microphone_channels, struct aec_t **);
+
+/* Release AEC object.
+ * This must be called when the audio device is closed. */
+void release_aec(struct aec_t* aec);
+
+/* Initialize reference configuration for AEC.
+ * Must be called when a new output stream is opened.
+ * Returns -EINVAL if any processing block fails to initialize,
+ * else returns 0. */
+int init_aec_reference_config (struct aec_t *aec, struct alsa_stream_out *out);
+
+/* Clear reference configuration for AEC.
+ * Must be called when the output stream is closed. */
+void destroy_aec_reference_config (struct aec_t *aec);
+
+/* Initialize microphone configuration for AEC.
+ * Must be called when a new input stream is opened.
+ * Returns -EINVAL if any processing block fails to initialize,
+ * else returns 0. */
+int init_aec_mic_config(struct aec_t* aec, struct alsa_stream_in* in);
+
+/* Clear microphone configuration for AEC.
+ * Must be called when the input stream is closed. */
+void destroy_aec_mic_config (struct aec_t *aec);
+
+/* Used to communicate playback state (running or not) to AEC interface.
+ * This is used by process_aec() to determine if AEC processing is to be run. */
+void aec_set_spk_running (struct aec_t *aec, bool state);
+
+/* Used to communicate playback state (running or not) to the caller. */
+bool aec_get_spk_running(struct aec_t* aec);
+
+/* Write audio samples to AEC reference FIFO for use in AEC.
+ * Both audio samples and timestamps are added in FIFO fashion.
+ * Must be called after every write to PCM.
+ * Returns -ENOMEM if the write fails, else returns 0. */
+int write_to_reference_fifo(struct aec_t* aec, void* buffer, struct aec_info* info);
+
+/* Get reference audio samples + timestamp, in the format expected by AEC,
+ * i.e. same sample rate and bit rate as microphone audio.
+ * Timestamp is updated in field 'timestamp_usec', and not in 'timestamp'.
+ * Returns:
+ *  -EINVAL    if the AEC object is invalid.
+ *  -ENOMEM    if the reference FIFO overflows or is corrupted.
+ *  -ETIMEDOUT if we timed out waiting for the requested number of bytes
+ *  0          otherwise */
+int get_reference_samples(struct aec_t* aec, void* buffer, struct aec_info* info);
+
+#ifdef AEC_HAL
+
+/* Processing function call for AEC.
+ * AEC output is updated at location pointed to by 'buffer'.
+ * This function does not run AEC when there is no playback -
+ * as communicated to this AEC interface using aec_set_spk_running().
+ * Returns -EINVAL if processing fails, else returns 0. */
+int process_aec(struct aec_t* aec, void* buffer, struct aec_info* info);
+
+#else /* #ifdef AEC_HAL */
+
+#define process_aec(...) ((int)0)
+
+#endif /* #ifdef AEC_HAL */
+
+#endif /* _AUDIO_AEC_H_ */