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Merge pull request #376 from oshoham/ring-buffer
Add ring buffers to AudioWorklet processors to support variable buffer sizes
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,125 @@ | ||
| /** | ||
| * Copyright 2018 Google LLC | ||
| * | ||
| * 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. | ||
| * | ||
| * A JS FIFO implementation for the AudioWorklet. 3 assumptions for the | ||
| * simpler operation: | ||
| * 1. the push and the pull operation are done by 128 frames. (Web Audio | ||
| * API's render quantum size in the speficiation) | ||
| * 2. the channel count of input/output cannot be changed dynamically. | ||
| * The AudioWorkletNode should be configured with the `.channelCount = k` | ||
| * (where k is the channel count you want) and | ||
| * `.channelCountMode = explicit`. | ||
| * 3. This is for the single-thread operation. (obviously) | ||
| * | ||
| * @class | ||
| */ | ||
| class RingBuffer { | ||
| /** | ||
| * @constructor | ||
| * @param {number} length Buffer length in frames. | ||
| * @param {number} channelCount Buffer channel count. | ||
| */ | ||
| constructor(length, channelCount) { | ||
| this._readIndex = 0; | ||
| this._writeIndex = 0; | ||
| this._framesAvailable = 0; | ||
|
|
||
| this._channelCount = channelCount; | ||
| this._length = length; | ||
| this._channelData = []; | ||
| for (let i = 0; i < this._channelCount; ++i) { | ||
| this._channelData[i] = new Float32Array(length); | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Getter for Available frames in buffer. | ||
| * | ||
| * @return {number} Available frames in buffer. | ||
| */ | ||
| get framesAvailable() { | ||
| return this._framesAvailable; | ||
| } | ||
|
|
||
| /** | ||
| * Push a sequence of Float32Arrays to buffer. | ||
| * | ||
| * @param {array} arraySequence A sequence of Float32Arrays. | ||
| */ | ||
| push(arraySequence) { | ||
| // The channel count of arraySequence and the length of each channel must | ||
| // match with this buffer obejct. | ||
|
|
||
| // Transfer data from the |arraySequence| storage to the internal buffer. | ||
| let sourceLength = arraySequence[0].length; | ||
| for (let i = 0; i < sourceLength; ++i) { | ||
| let writeIndex = (this._writeIndex + i) % this._length; | ||
| for (let channel = 0; channel < this._channelCount; ++channel) { | ||
| this._channelData[channel][writeIndex] = arraySequence[channel][i]; | ||
| } | ||
| } | ||
|
|
||
| this._writeIndex += sourceLength; | ||
| if (this._writeIndex >= this._length) { | ||
| this._writeIndex = 0; | ||
| } | ||
|
|
||
| // For excessive frames, the buffer will be overwritten. | ||
| this._framesAvailable += sourceLength; | ||
| if (this._framesAvailable > this._length) { | ||
| this._framesAvailable = this._length; | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Pull data out of buffer and fill a given sequence of Float32Arrays. | ||
| * | ||
| * @param {array} arraySequence An array of Float32Arrays. | ||
| */ | ||
| pull(arraySequence) { | ||
| // The channel count of arraySequence and the length of each channel must | ||
| // match with this buffer obejct. | ||
|
|
||
| // If the FIFO is completely empty, do nothing. | ||
| if (this._framesAvailable === 0) { | ||
| return; | ||
| } | ||
|
|
||
| let destinationLength = arraySequence[0].length; | ||
|
|
||
| // Transfer data from the internal buffer to the |arraySequence| storage. | ||
| for (let i = 0; i < destinationLength; ++i) { | ||
| let readIndex = (this._readIndex + i) % this._length; | ||
| for (let channel = 0; channel < this._channelCount; ++channel) { | ||
| arraySequence[channel][i] = this._channelData[channel][readIndex]; | ||
| } | ||
| } | ||
|
|
||
| this._readIndex += destinationLength; | ||
| if (this._readIndex >= this._length) { | ||
| this._readIndex = 0; | ||
| } | ||
|
|
||
| this._framesAvailable -= destinationLength; | ||
| if (this._framesAvailable < 0) { | ||
| this._framesAvailable = 0; | ||
| } | ||
| } | ||
| } | ||
|
|
||
| // export an object for compatibility with preval.require() | ||
| module.exports = { | ||
| default: RingBuffer | ||
| }; |
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