sinc_resampler.cc | Explore in Territory

/*
 *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

// Modified from the Chromium original:
// src/media/base/sinc_resampler.cc

// Initial input buffer layout, dividing into regions r0_ to r4_ (note: r0_, r3_
// and r4_ will move after the first load):
//
// |----------------|-----------------------------------------|----------------|
//
//                                        request_frames_
//                   <--------------------------------------------------------->
//                                    r0_ (during first load)
//
//  kKernelSize / 2   kKernelSize / 2         kKernelSize / 2   kKernelSize / 2
// <---------------> <--------------->       <---------------> <--------------->
//        r1_               r2_                     r3_               r4_
//
//                             block_size_ == r4_ - r2_
//                   <--------------------------------------->
//
//                                                  request_frames_
//                                    <------------------ ... ----------------->
//                                               r0_ (during second load)
//
// On the second request r0_ slides to the right by kKernelSize / 2 and r3_, r4_
// and block_size_ are reinitialized via step (3) in the algorithm below.
//
// These new regions remain constant until a Flush() occurs.  While complicated,
// this allows us to reduce jitter by always requesting the same amount from the
// provided callback.
//
// The algorithm:
//
// 1) Allocate input_buffer of size: request_frames_ + kKernelSize; this ensures
//    there's enough room to read request_frames_ from the callback into region
//    r0_ (which will move between the first and subsequent passes).
//
// 2) Let r1_, r2_ each represent half the kernel centered around r0_:
//
//        r0_ = input_buffer_ + kKernelSize / 2
//        r1_ = input_buffer_
//        r2_ = r0_
//
//    r0_ is always request_frames_ in size.  r1_, r2_ are kKernelSize / 2 in
//    size.  r1_ must be zero initialized to avoid convolution with garbage (see
//    step (5) for why).
//
// 3) Let r3_, r4_ each represent half the kernel right aligned with the end of
//    r0_ and choose block_size_ as the distance in frames between r4_ and r2_:
//
//        r3_ = r0_ + request_frames_ - kKernelSize
//        r4_ = r0_ + request_frames_ - kKernelSize / 2
//        block_size_ = r4_ - r2_ = request_frames_ - kKernelSize / 2
//
// 4) Consume request_frames_ frames into r0_.
//
// 5) Position kernel centered at start of r2_ and generate output frames until
//    the kernel is centered at the start of r4_ or we've finished generating
//    all the output frames.
//
// 6) Wrap left over data from the r3_ to r1_ and r4_ to r2_.
//
// 7) If we're on the second load, in order to avoid overwriting the frames we
//    just wrapped from r4_ we need to slide r0_ to the right by the size of
//    r4_, which is kKernelSize / 2:
//
//        r0_ = r0_ + kKernelSize / 2 = input_buffer_ + kKernelSize
//
//    r3_, r4_, and block_size_ then need to be reinitialized, so goto (3).
//
// 8) Else, if we're not on the second load, goto (4).
//
// Note: we're glossing over how the sub-sample handling works with
// `virtual_source_idx_`, etc.

// MSVC++ requires this to be set before any other includes to get M_PI.
#define _USE_MATH_DEFINES

#include "common_audio/resampler/sinc_resampler.h"

#include <math.h>
#include <stdint.h>
#include <string.h>

#include <limits>

#include "rtc_base/checks.h"
#include "rtc_base/system/arch.h"
#include "system_wrappers/include/cpu_features_wrapper.h"  // kSSE2, WebRtc_G...

namespace webrtc {

namespace {

double SincScaleFactor(double io_ratio) { … }

}  // namespace

const size_t SincResampler::kKernelSize;

// If we know the minimum architecture at compile time, avoid CPU detection.
void SincResampler::InitializeCPUSpecificFeatures() { … }

SincResampler::SincResampler(double io_sample_rate_ratio,
                             size_t request_frames,
                             SincResamplerCallback* read_cb)
    : … { … }

SincResampler::~SincResampler() { … }

void SincResampler::UpdateRegions(bool second_load) { … }

void SincResampler::InitializeKernel() { … }

void SincResampler::SetRatio(double io_sample_rate_ratio) { … }

void SincResampler::Resample(size_t frames, float* destination) { … }

#undef CONVOLVE_FUNC

size_t SincResampler::ChunkSize() const { … }

void SincResampler::Flush() { … }

float SincResampler::Convolve_C(const float* input_ptr,
                                const float* k1,
                                const float* k2,
                                double kernel_interpolation_factor) { … }

}  // namespace webrtc
chromium/third_party/webrtc/common_audio/resampler/sinc_resampler.cc
