The Tor Browser: content/media/webaudio/blink/HRTFKernel.cpp@6474c204b198

Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.

     1 /*

     2  * Copyright (C) 2010 Google Inc. All rights reserved.

     3  *

     4  * Redistribution and use in source and binary forms, with or without

     5  * modification, are permitted provided that the following conditions

     6  * are met:

     7  *

     8  * 1.  Redistributions of source code must retain the above copyright

     9  *     notice, this list of conditions and the following disclaimer.

    10  * 2.  Redistributions in binary form must reproduce the above copyright

    11  *     notice, this list of conditions and the following disclaimer in the

    12  *     documentation and/or other materials provided with the distribution.

    13  * 3.  Neither the name of Apple Computer, Inc. ("Apple") nor the names of

    14  *     its contributors may be used to endorse or promote products derived

    15  *     from this software without specific prior written permission.

    16  *

    17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY

    18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED

    19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE

    20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY

    21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES

    22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;

    23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND

    24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT

    25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF

    26  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

    27  */

    29 #include "HRTFKernel.h"

    30 namespace WebCore {

    32 // Takes the input audio channel |impulseP| as an input impulse response and calculates the average group delay.

    33 // This represents the initial delay before the most energetic part of the impulse response.

    34 // The sample-frame delay is removed from the |impulseP| impulse response, and this value  is returned.

    35 // The |length| of the passed in |impulseP| must be must be a power of 2.

    36 static float extractAverageGroupDelay(float* impulseP, size_t length)

    37 {

    38     // Check for power-of-2.

    39     MOZ_ASSERT(length && (length & (length - 1)) == 0);

    41     FFTBlock estimationFrame(length);

    42     estimationFrame.PerformFFT(impulseP);

    44     float frameDelay = static_cast<float>(estimationFrame.ExtractAverageGroupDelay());

    45     estimationFrame.GetInverse(impulseP);

    47     return frameDelay;

    48 }

    50 HRTFKernel::HRTFKernel(float* impulseResponse, size_t length, float sampleRate)

    51     : m_frameDelay(0)

    52     , m_sampleRate(sampleRate)

    53 {

    54     // Determine the leading delay (average group delay) for the response.

    55     m_frameDelay = extractAverageGroupDelay(impulseResponse, length);

    57     // The FFT size (with zero padding) needs to be twice the response length

    58     // in order to do proper convolution.

    59     unsigned fftSize = 2 * length;

    61     // Quick fade-out (apply window) at truncation point

    62     // because the impulse response has been truncated.

    63     unsigned numberOfFadeOutFrames = static_cast<unsigned>(sampleRate / 4410); // 10 sample-frames @44.1KHz sample-rate

    64     MOZ_ASSERT(numberOfFadeOutFrames < length);

    65     if (numberOfFadeOutFrames < length) {

    66         for (unsigned i = length - numberOfFadeOutFrames; i < length; ++i) {

    67             float x = 1.0f - static_cast<float>(i - (length - numberOfFadeOutFrames)) / numberOfFadeOutFrames;

    68             impulseResponse[i] *= x;

    69         }

    70     }

    72     m_fftFrame = new FFTBlock(fftSize);

    73     m_fftFrame->PadAndMakeScaledDFT(impulseResponse, length);

    74 }

    76 // Interpolates two kernels with x: 0 -> 1 and returns the result.

    77 nsReturnRef<HRTFKernel> HRTFKernel::createInterpolatedKernel(HRTFKernel* kernel1, HRTFKernel* kernel2, float x)

    78 {

    79     MOZ_ASSERT(kernel1 && kernel2);

    80     if (!kernel1 || !kernel2)

    81         return nsReturnRef<HRTFKernel>();

    83     MOZ_ASSERT(x >= 0.0 && x < 1.0);

    84     x = mozilla::clamped(x, 0.0f, 1.0f);

    86     float sampleRate1 = kernel1->sampleRate();

    87     float sampleRate2 = kernel2->sampleRate();

    88     MOZ_ASSERT(sampleRate1 == sampleRate2);

    89     if (sampleRate1 != sampleRate2)

    90         return nsReturnRef<HRTFKernel>();

    92     float frameDelay = (1 - x) * kernel1->frameDelay() + x * kernel2->frameDelay();

    94     nsAutoPtr<FFTBlock> interpolatedFrame(

    95         FFTBlock::CreateInterpolatedBlock(*kernel1->fftFrame(), *kernel2->fftFrame(), x));

    96     return HRTFKernel::create(interpolatedFrame, frameDelay, sampleRate1);

    97 }

    99 } // namespace WebCore

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