media/libeffects/visualizer/aidl/VisualizerContext.cpp - LeafOS-Project/android_frameworks_av - Gitiles

 /*
  * Copyright (C) 2022 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.
  */

 #include "VisualizerContext.h"

 #include <algorithm>
 #include <math.h>
 #include <time.h>

 #include <android/binder_status.h>
 #include <audio_utils/primitives.h>
 #include <system/audio.h>
 #include <Utils.h>

 #ifndef BUILD_FLOAT
         #error AIDL Visualizer only support float 32bits, make sure add cflags -DBUILD_FLOAT,
 #endif

 using aidl::android::hardware::audio::common::getChannelCount;

 namespace aidl::android::hardware::audio::effect {

 VisualizerContext::VisualizerContext(int statusDepth, const Parameter::Common& common)
     : EffectContext(statusDepth, common) {
 }

 VisualizerContext::~VisualizerContext() {
     std::lock_guard lg(mMutex);
     LOG(DEBUG) << __func__;
     mState = State::UNINITIALIZED;
 }

 RetCode VisualizerContext::initParams(const Parameter::Common& common) {
     std::lock_guard lg(mMutex);
     LOG(DEBUG) << __func__;
     if (common.input != common.output) {
         LOG(ERROR) << __func__ << " mismatch input: " << common.input.toString()
                    << " and output: " << common.output.toString();
         return RetCode::ERROR_ILLEGAL_PARAMETER;
     }

     mState = State::INITIALIZED;
     auto channelCount = getChannelCount(common.input.base.channelMask);
 #ifdef SUPPORT_MC
     if (channelCount < 1 || channelCount > FCC_LIMIT) return RetCode::ERROR_ILLEGAL_PARAMETER;
 #else
     if (channelCount != FCC_2) return RetCode::ERROR_ILLEGAL_PARAMETER;
 #endif
     mChannelCount = channelCount;
     mCommon = common;
     std::fill(mCaptureBuf.begin(), mCaptureBuf.end(), 0x80);
     return RetCode::SUCCESS;
 }

 RetCode VisualizerContext::enable() {
     std::lock_guard lg(mMutex);
     if (mState != State::INITIALIZED) {
         return RetCode::ERROR_EFFECT_LIB_ERROR;
     }
     mState = State::ACTIVE;
     return RetCode::SUCCESS;
 }

 RetCode VisualizerContext::disable() {
     std::lock_guard lg(mMutex);
     if (mState != State::ACTIVE) {
         return RetCode::ERROR_EFFECT_LIB_ERROR;
     }
     mState = State::INITIALIZED;
     return RetCode::SUCCESS;
 }

 void VisualizerContext::reset() {
     std::lock_guard lg(mMutex);
     std::fill(mCaptureBuf.begin(), mCaptureBuf.end(), 0x80);
 }

 RetCode VisualizerContext::setCaptureSamples(int samples) {
     std::lock_guard lg(mMutex);
     mCaptureSamples = samples;
     return RetCode::SUCCESS;
 }
 int VisualizerContext::getCaptureSamples() {
     std::lock_guard lg(mMutex);
     return mCaptureSamples;
 }

 RetCode VisualizerContext::setMeasurementMode(Visualizer::MeasurementMode mode) {
     std::lock_guard lg(mMutex);
     mMeasurementMode = mode;
     return RetCode::SUCCESS;
 }
 Visualizer::MeasurementMode VisualizerContext::getMeasurementMode() {
     std::lock_guard lg(mMutex);
     return mMeasurementMode;
 }

 RetCode VisualizerContext::setScalingMode(Visualizer::ScalingMode mode) {
     std::lock_guard lg(mMutex);
     mScalingMode = mode;
     return RetCode::SUCCESS;
 }
 Visualizer::ScalingMode VisualizerContext::getScalingMode() {
     std::lock_guard lg(mMutex);
     return mScalingMode;
 }

 RetCode VisualizerContext::setDownstreamLatency(int latency) {
     std::lock_guard lg(mMutex);
     mDownstreamLatency = latency;
     return RetCode::SUCCESS;
 }

 int VisualizerContext::getDownstreamLatency() {
     std::lock_guard lg(mMutex);
     return mDownstreamLatency;
 }

 uint32_t VisualizerContext::getDeltaTimeMsFromUpdatedTime_l() {
     uint32_t deltaMs = 0;
     if (mBufferUpdateTime.tv_sec != 0) {
         struct timespec ts;
         if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0) {
             time_t secs = ts.tv_sec - mBufferUpdateTime.tv_sec;
             long nsec = ts.tv_nsec - mBufferUpdateTime.tv_nsec;
             if (nsec < 0) {
                 --secs;
                 nsec += 1000000000;
             }
             deltaMs = secs * 1000 + nsec / 1000000;
         }
     }
     return deltaMs;
 }

 Visualizer::Measurement VisualizerContext::getMeasure() {
     uint16_t peakU16 = 0;
     float sumRmsSquared = 0.0f;
     uint8_t nbValidMeasurements = 0;

     {
         std::lock_guard lg(mMutex);
         // reset measurements if last measurement was too long ago (which implies stored
         // measurements aren't relevant anymore and shouldn't bias the new one)
         const uint32_t delayMs = getDeltaTimeMsFromUpdatedTime_l();
         if (delayMs > kDiscardMeasurementsTimeMs) {
             LOG(INFO) << __func__ << " Discarding " << delayMs << " ms old measurements";
             for (uint32_t i = 0; i < mMeasurementWindowSizeInBuffers; i++) {
                 mPastMeasurements[i].mIsValid = false;
                 mPastMeasurements[i].mPeakU16 = 0;
                 mPastMeasurements[i].mRmsSquared = 0;
             }
             mMeasurementBufferIdx = 0;
         } else {
             // only use actual measurements, otherwise the first RMS measure happening before
             // MEASUREMENT_WINDOW_MAX_SIZE_IN_BUFFERS have been played will always be artificially
             // low
             for (uint32_t i = 0; i < mMeasurementWindowSizeInBuffers; i++) {
                 if (mPastMeasurements[i].mIsValid) {
                     if (mPastMeasurements[i].mPeakU16 > peakU16) {
                         peakU16 = mPastMeasurements[i].mPeakU16;
                     }
                     sumRmsSquared += mPastMeasurements[i].mRmsSquared;
                     nbValidMeasurements++;
                 }
             }
         }
     }

     float rms = nbValidMeasurements == 0 ? 0.0f : sqrtf(sumRmsSquared / nbValidMeasurements);
     Visualizer::Measurement measure;
     // convert from I16 sample values to mB and write results
     measure.rms = (rms < 0.000016f) ? -9600 : (int32_t)(2000 * log10(rms / 32767.0f));
     measure.peak = (peakU16 == 0) ? -9600 : (int32_t)(2000 * log10(peakU16 / 32767.0f));
     LOG(INFO) << __func__ << " peak " << peakU16 << " (" << measure.peak << "mB), rms " << rms
               << " (" << measure.rms << "mB)";
     return measure;
 }

 std::vector<uint8_t> VisualizerContext::capture() {
     std::lock_guard lg(mMutex);
     uint32_t captureSamples = mCaptureSamples;
     std::vector<uint8_t> result(captureSamples, 0x80);
     // cts android.media.audio.cts.VisualizerTest expecting silence data when effect not running
     // RETURN_VALUE_IF(mState != State::ACTIVE, result, "illegalState");
     if (mState != State::ACTIVE) {
         return result;
     }

     const uint32_t deltaMs = getDeltaTimeMsFromUpdatedTime_l();
     // if audio framework has stopped playing audio although the effect is still active we must
     // clear the capture buffer to return silence
     if ((mLastCaptureIdx == mCaptureIdx) && (mBufferUpdateTime.tv_sec != 0) &&
         (deltaMs > kMaxStallTimeMs)) {
         LOG(INFO) << __func__ << " capture going to idle";
         mBufferUpdateTime.tv_sec = 0;
         return result;
     }
     int32_t latencyMs = mDownstreamLatency;
     latencyMs -= deltaMs;
     if (latencyMs < 0) {
         latencyMs = 0;
     }
     uint32_t deltaSamples = captureSamples + mCommon.input.base.sampleRate * latencyMs / 1000;

     // large sample rate, latency, or capture size, could cause overflow.
     // do not offset more than the size of buffer.
     if (deltaSamples > kMaxCaptureBufSize) {
         android_errorWriteLog(0x534e4554, "31781965");
         deltaSamples = kMaxCaptureBufSize;
     }

     int32_t capturePoint;
     __builtin_sub_overflow((int32_t) mCaptureIdx, deltaSamples, &capturePoint);
     // a negative capturePoint means we wrap the buffer.
     if (capturePoint < 0) {
         uint32_t size = -capturePoint;
         if (size > captureSamples) {
             size = captureSamples;
         }
         std::copy(std::begin(mCaptureBuf) + kMaxCaptureBufSize - size,
                   std::begin(mCaptureBuf) + kMaxCaptureBufSize, result.begin());
         captureSamples -= size;
         capturePoint = 0;
     }
     std::copy(std::begin(mCaptureBuf) + capturePoint,
               std::begin(mCaptureBuf) + capturePoint + captureSamples,
               result.begin() + mCaptureSamples - captureSamples);
     mLastCaptureIdx = mCaptureIdx;
     return result;
 }

 IEffect::Status VisualizerContext::process(float* in, float* out, int samples) {
     IEffect::Status result = {STATUS_NOT_ENOUGH_DATA, 0, 0};
     RETURN_VALUE_IF(in == nullptr || out == nullptr || samples == 0, result, "dataBufferError");

     std::lock_guard lg(mMutex);
     result.status = STATUS_INVALID_OPERATION;
     RETURN_VALUE_IF(mState != State::ACTIVE, result, "stateNotActive");
     LOG(DEBUG) << __func__ << " in " << in << " out " << out << " sample " << samples;
     // perform measurements if needed
     if (mMeasurementMode == Visualizer::MeasurementMode::PEAK_RMS) {
         // find the peak and RMS squared for the new buffer
         float rmsSqAcc = 0;
         float maxSample = 0.f;
         for (size_t inIdx = 0; inIdx < (unsigned) samples; ++inIdx) {
             maxSample = fmax(maxSample, fabs(in[inIdx]));
             rmsSqAcc += in[inIdx] * in[inIdx];
         }
         maxSample *= 1 << 15; // scale to int16_t, with exactly 1 << 15 representing positive num.
         rmsSqAcc *= 1 << 30; // scale to int16_t * 2
         mPastMeasurements[mMeasurementBufferIdx] = {.mIsValid = true,
                                                     .mPeakU16 = (uint16_t)maxSample,
                                                     .mRmsSquared = rmsSqAcc / samples};
         if (++mMeasurementBufferIdx >= mMeasurementWindowSizeInBuffers) {
             mMeasurementBufferIdx = 0;
         }
     }

     float fscale;  // multiplicative scale
     if (mScalingMode == Visualizer::ScalingMode::NORMALIZED) {
         // derive capture scaling factor from peak value in current buffer
         // this gives more interesting captures for display.
         float maxSample = 0.f;
         for (size_t inIdx = 0; inIdx < (unsigned)samples; ) {
             // we reconstruct the actual summed value to ensure proper normalization
             // for multichannel outputs (channels > 2 may often be 0).
             float smp = 0.f;
             for (int i = 0; i < mChannelCount; ++i) {
                 smp += in[inIdx++];
             }
             maxSample = fmax(maxSample, fabs(smp));
         }
         if (maxSample > 0.f) {
             fscale = 0.99f / maxSample;
             int exp; // unused
             const float significand = frexp(fscale, &exp);
             if (significand == 0.5f) {
                 fscale *= 255.f / 256.f; // avoid returning unaltered PCM signal
             }
         } else {
             // scale doesn't matter, the values are all 0.
             fscale = 1.f;
         }
     } else {
         assert(mScalingMode == Visualizer::ScalingMode::AS_PLAYED);
         // Note: if channels are uncorrelated, 1/sqrt(N) could be used at the risk of clipping.
         fscale = 1.f / mChannelCount;  // account for summing all the channels together.
     }

     uint32_t captIdx;
     uint32_t inIdx;
     for (inIdx = 0, captIdx = mCaptureIdx; inIdx < (unsigned)samples; captIdx++) {
         // wrap
         if (captIdx >= kMaxCaptureBufSize) {
             captIdx = 0;
         }

         float smp = 0.f;
         for (uint32_t i = 0; i < mChannelCount; ++i) {
             smp += in[inIdx++];
         }
         mCaptureBuf[captIdx] = clamp8_from_float(smp * fscale);
     }

     // the following two should really be atomic, though it probably doesn't
     // matter much for visualization purposes
     mCaptureIdx = captIdx;
     // update last buffer update time stamp
     if (clock_gettime(CLOCK_MONOTONIC, &mBufferUpdateTime) < 0) {
         mBufferUpdateTime.tv_sec = 0;
     }

     // TODO: handle access_mode
     memcpy(out, in, samples * sizeof(float));
     return {STATUS_OK, samples, samples};
 }

 }  // namespace aidl::android::hardware::audio::effect
	/*
	* Copyright (C) 2022 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.
	*/

	#include "VisualizerContext.h"

	#include <algorithm>
	#include <math.h>
	#include <time.h>

	#include <android/binder_status.h>
	#include <audio_utils/primitives.h>
	#include <system/audio.h>
	#include <Utils.h>

	#ifndef BUILD_FLOAT
	#error AIDL Visualizer only support float 32bits, make sure add cflags -DBUILD_FLOAT,
	#endif

	using aidl::android::hardware::audio::common::getChannelCount;

	namespace aidl::android::hardware::audio::effect {

	VisualizerContext::VisualizerContext(int statusDepth, const Parameter::Common& common)
	: EffectContext(statusDepth, common) {
	}

	VisualizerContext::~VisualizerContext() {
	std::lock_guard lg(mMutex);
	LOG(DEBUG) << __func__;
	mState = State::UNINITIALIZED;
	}

	RetCode VisualizerContext::initParams(const Parameter::Common& common) {
	std::lock_guard lg(mMutex);
	LOG(DEBUG) << __func__;
	if (common.input != common.output) {
	LOG(ERROR) << __func__ << " mismatch input: " << common.input.toString()
	<< " and output: " << common.output.toString();
	return RetCode::ERROR_ILLEGAL_PARAMETER;
	}

	mState = State::INITIALIZED;
	auto channelCount = getChannelCount(common.input.base.channelMask);
	#ifdef SUPPORT_MC
	if (channelCount < 1 \|\| channelCount > FCC_LIMIT) return RetCode::ERROR_ILLEGAL_PARAMETER;
	#else
	if (channelCount != FCC_2) return RetCode::ERROR_ILLEGAL_PARAMETER;
	#endif
	mChannelCount = channelCount;
	mCommon = common;
	std::fill(mCaptureBuf.begin(), mCaptureBuf.end(), 0x80);
	return RetCode::SUCCESS;
	}

	RetCode VisualizerContext::enable() {
	std::lock_guard lg(mMutex);
	if (mState != State::INITIALIZED) {
	return RetCode::ERROR_EFFECT_LIB_ERROR;
	}
	mState = State::ACTIVE;
	return RetCode::SUCCESS;
	}

	RetCode VisualizerContext::disable() {
	std::lock_guard lg(mMutex);
	if (mState != State::ACTIVE) {
	return RetCode::ERROR_EFFECT_LIB_ERROR;
	}
	mState = State::INITIALIZED;
	return RetCode::SUCCESS;
	}

	void VisualizerContext::reset() {
	std::lock_guard lg(mMutex);
	std::fill(mCaptureBuf.begin(), mCaptureBuf.end(), 0x80);
	}

	RetCode VisualizerContext::setCaptureSamples(int samples) {
	std::lock_guard lg(mMutex);
	mCaptureSamples = samples;
	return RetCode::SUCCESS;
	}
	int VisualizerContext::getCaptureSamples() {
	std::lock_guard lg(mMutex);
	return mCaptureSamples;
	}

	RetCode VisualizerContext::setMeasurementMode(Visualizer::MeasurementMode mode) {
	std::lock_guard lg(mMutex);
	mMeasurementMode = mode;
	return RetCode::SUCCESS;
	}
	Visualizer::MeasurementMode VisualizerContext::getMeasurementMode() {
	std::lock_guard lg(mMutex);
	return mMeasurementMode;
	}

	RetCode VisualizerContext::setScalingMode(Visualizer::ScalingMode mode) {
	std::lock_guard lg(mMutex);
	mScalingMode = mode;
	return RetCode::SUCCESS;
	}
	Visualizer::ScalingMode VisualizerContext::getScalingMode() {
	std::lock_guard lg(mMutex);
	return mScalingMode;
	}

	RetCode VisualizerContext::setDownstreamLatency(int latency) {
	std::lock_guard lg(mMutex);
	mDownstreamLatency = latency;
	return RetCode::SUCCESS;
	}

	int VisualizerContext::getDownstreamLatency() {
	std::lock_guard lg(mMutex);
	return mDownstreamLatency;
	}

	uint32_t VisualizerContext::getDeltaTimeMsFromUpdatedTime_l() {
	uint32_t deltaMs = 0;
	if (mBufferUpdateTime.tv_sec != 0) {
	struct timespec ts;
	if (clock_gettime(CLOCK_MONOTONIC, &ts) == 0) {
	time_t secs = ts.tv_sec - mBufferUpdateTime.tv_sec;
	long nsec = ts.tv_nsec - mBufferUpdateTime.tv_nsec;
	if (nsec < 0) {
	--secs;
	nsec += 1000000000;
	}
	deltaMs = secs * 1000 + nsec / 1000000;
	}
	}
	return deltaMs;
	}

	Visualizer::Measurement VisualizerContext::getMeasure() {
	uint16_t peakU16 = 0;
	float sumRmsSquared = 0.0f;
	uint8_t nbValidMeasurements = 0;

	{
	std::lock_guard lg(mMutex);
	// reset measurements if last measurement was too long ago (which implies stored
	// measurements aren't relevant anymore and shouldn't bias the new one)
	const uint32_t delayMs = getDeltaTimeMsFromUpdatedTime_l();
	if (delayMs > kDiscardMeasurementsTimeMs) {
	LOG(INFO) << __func__ << " Discarding " << delayMs << " ms old measurements";
	for (uint32_t i = 0; i < mMeasurementWindowSizeInBuffers; i++) {
	mPastMeasurements[i].mIsValid = false;
	mPastMeasurements[i].mPeakU16 = 0;
	mPastMeasurements[i].mRmsSquared = 0;
	}
	mMeasurementBufferIdx = 0;
	} else {
	// only use actual measurements, otherwise the first RMS measure happening before
	// MEASUREMENT_WINDOW_MAX_SIZE_IN_BUFFERS have been played will always be artificially
	// low
	for (uint32_t i = 0; i < mMeasurementWindowSizeInBuffers; i++) {
	if (mPastMeasurements[i].mIsValid) {
	if (mPastMeasurements[i].mPeakU16 > peakU16) {
	peakU16 = mPastMeasurements[i].mPeakU16;
	}
	sumRmsSquared += mPastMeasurements[i].mRmsSquared;
	nbValidMeasurements++;
	}
	}
	}
	}

	float rms = nbValidMeasurements == 0 ? 0.0f : sqrtf(sumRmsSquared / nbValidMeasurements);
	Visualizer::Measurement measure;
	// convert from I16 sample values to mB and write results
	measure.rms = (rms < 0.000016f) ? -9600 : (int32_t)(2000 * log10(rms / 32767.0f));
	measure.peak = (peakU16 == 0) ? -9600 : (int32_t)(2000 * log10(peakU16 / 32767.0f));
	LOG(INFO) << __func__ << " peak " << peakU16 << " (" << measure.peak << "mB), rms " << rms
	<< " (" << measure.rms << "mB)";
	return measure;
	}

	std::vector<uint8_t> VisualizerContext::capture() {
	std::lock_guard lg(mMutex);
	uint32_t captureSamples = mCaptureSamples;
	std::vector<uint8_t> result(captureSamples, 0x80);
	// cts android.media.audio.cts.VisualizerTest expecting silence data when effect not running
	// RETURN_VALUE_IF(mState != State::ACTIVE, result, "illegalState");
	if (mState != State::ACTIVE) {
	return result;
	}

	const uint32_t deltaMs = getDeltaTimeMsFromUpdatedTime_l();
	// if audio framework has stopped playing audio although the effect is still active we must
	// clear the capture buffer to return silence
	if ((mLastCaptureIdx == mCaptureIdx) && (mBufferUpdateTime.tv_sec != 0) &&
	(deltaMs > kMaxStallTimeMs)) {
	LOG(INFO) << __func__ << " capture going to idle";
	mBufferUpdateTime.tv_sec = 0;
	return result;
	}
	int32_t latencyMs = mDownstreamLatency;
	latencyMs -= deltaMs;
	if (latencyMs < 0) {
	latencyMs = 0;
	}
	uint32_t deltaSamples = captureSamples + mCommon.input.base.sampleRate * latencyMs / 1000;

	// large sample rate, latency, or capture size, could cause overflow.
	// do not offset more than the size of buffer.
	if (deltaSamples > kMaxCaptureBufSize) {
	android_errorWriteLog(0x534e4554, "31781965");
	deltaSamples = kMaxCaptureBufSize;
	}

	int32_t capturePoint;
	__builtin_sub_overflow((int32_t) mCaptureIdx, deltaSamples, &capturePoint);
	// a negative capturePoint means we wrap the buffer.
	if (capturePoint < 0) {
	uint32_t size = -capturePoint;
	if (size > captureSamples) {
	size = captureSamples;
	}
	std::copy(std::begin(mCaptureBuf) + kMaxCaptureBufSize - size,
	std::begin(mCaptureBuf) + kMaxCaptureBufSize, result.begin());
	captureSamples -= size;
	capturePoint = 0;
	}
	std::copy(std::begin(mCaptureBuf) + capturePoint,
	std::begin(mCaptureBuf) + capturePoint + captureSamples,
	result.begin() + mCaptureSamples - captureSamples);
	mLastCaptureIdx = mCaptureIdx;
	return result;
	}

	IEffect::Status VisualizerContext::process(float* in, float* out, int samples) {
	IEffect::Status result = {STATUS_NOT_ENOUGH_DATA, 0, 0};
	RETURN_VALUE_IF(in == nullptr \|\| out == nullptr \|\| samples == 0, result, "dataBufferError");

	std::lock_guard lg(mMutex);
	result.status = STATUS_INVALID_OPERATION;
	RETURN_VALUE_IF(mState != State::ACTIVE, result, "stateNotActive");
	LOG(DEBUG) << __func__ << " in " << in << " out " << out << " sample " << samples;
	// perform measurements if needed
	if (mMeasurementMode == Visualizer::MeasurementMode::PEAK_RMS) {
	// find the peak and RMS squared for the new buffer
	float rmsSqAcc = 0;
	float maxSample = 0.f;
	for (size_t inIdx = 0; inIdx < (unsigned) samples; ++inIdx) {
	maxSample = fmax(maxSample, fabs(in[inIdx]));
	rmsSqAcc += in[inIdx] * in[inIdx];
	}
	maxSample *= 1 << 15; // scale to int16_t, with exactly 1 << 15 representing positive num.
	rmsSqAcc = 1 << 30; // scale to int16_t 2
	mPastMeasurements[mMeasurementBufferIdx] = {.mIsValid = true,
	.mPeakU16 = (uint16_t)maxSample,
	.mRmsSquared = rmsSqAcc / samples};
	if (++mMeasurementBufferIdx >= mMeasurementWindowSizeInBuffers) {
	mMeasurementBufferIdx = 0;
	}
	}

	float fscale; // multiplicative scale
	if (mScalingMode == Visualizer::ScalingMode::NORMALIZED) {
	// derive capture scaling factor from peak value in current buffer
	// this gives more interesting captures for display.
	float maxSample = 0.f;
	for (size_t inIdx = 0; inIdx < (unsigned)samples; ) {
	// we reconstruct the actual summed value to ensure proper normalization
	// for multichannel outputs (channels > 2 may often be 0).
	float smp = 0.f;
	for (int i = 0; i < mChannelCount; ++i) {
	smp += in[inIdx++];
	}
	maxSample = fmax(maxSample, fabs(smp));
	}
	if (maxSample > 0.f) {
	fscale = 0.99f / maxSample;
	int exp; // unused
	const float significand = frexp(fscale, &exp);
	if (significand == 0.5f) {
	fscale *= 255.f / 256.f; // avoid returning unaltered PCM signal
	}
	} else {
	// scale doesn't matter, the values are all 0.
	fscale = 1.f;
	}
	} else {
	assert(mScalingMode == Visualizer::ScalingMode::AS_PLAYED);
	// Note: if channels are uncorrelated, 1/sqrt(N) could be used at the risk of clipping.
	fscale = 1.f / mChannelCount; // account for summing all the channels together.
	}

	uint32_t captIdx;
	uint32_t inIdx;
	for (inIdx = 0, captIdx = mCaptureIdx; inIdx < (unsigned)samples; captIdx++) {
	// wrap
	if (captIdx >= kMaxCaptureBufSize) {
	captIdx = 0;
	}

	float smp = 0.f;
	for (uint32_t i = 0; i < mChannelCount; ++i) {
	smp += in[inIdx++];
	}
	mCaptureBuf[captIdx] = clamp8_from_float(smp * fscale);
	}

	// the following two should really be atomic, though it probably doesn't
	// matter much for visualization purposes
	mCaptureIdx = captIdx;
	// update last buffer update time stamp
	if (clock_gettime(CLOCK_MONOTONIC, &mBufferUpdateTime) < 0) {
	mBufferUpdateTime.tv_sec = 0;
	}

	// TODO: handle access_mode
	memcpy(out, in, samples * sizeof(float));
	return {STATUS_OK, samples, samples};
	}

	} // namespace aidl::android::hardware::audio::effect