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chrisnchrisn
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Added slice method
See #84
1 parent fe7bb04 commit 84fc4ea

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Lines changed: 189 additions & 2 deletions

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‎doc/API.md‎

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@@ -16,6 +16,7 @@
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* [.channel](#waveformDatachannelindex)
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* [.resample](#waveformDataresampleoptions)
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* [.concat](#waveformDataconcatwaveforms)
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* [.slice](#waveformDatasliceoptions)
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* [.toJSON](#waveformDatatojson)
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* [.toArrayBuffer](#waveformDatatoarraybuffer)
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* [WaveformDataChannel](#waveformdatachannel)
@@ -468,6 +469,38 @@ console.log(wave3.length); // -> 100
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console.log(combinedResult.length); // -> 900
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```
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### waveformData.slice(options)
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Returns a subset of the waveform data between a given start and end point.
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#### Arguments
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| Name | Type |
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| --------- | ------------------------------------ |
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| `options` | An object containing either `startIndex` and `endIndex` values, which give the start and end indexes in the waveform data, or `startTime` and `endTime`, which give the start and end times (in seconds) |
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#### Example
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Return the waveform between index 100 and index 200:
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```javascript
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const waveform = WaveformData.create(buffer);
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const slice = waveform.slice({ startIndex: 100, endIndex: 200 });
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console.log(slice.length); // -> 100
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```
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Return the waveform between 1.0 and 2.0 seconds:
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```javascript
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const waveform = WaveformData.create(buffer);
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const slice = waveform.slice({ startTime: 1.0, endTime: 2.0 });
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console.log(slice.length); // -> 86
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```
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## waveformData.toJSON()
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Returns an object containing the waveform data.

‎src/waveform-data.js‎

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@@ -423,6 +423,70 @@ WaveformData.prototype = {
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return totalBuffer;
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},
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slice: function(options) {
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var startIndex = 0;
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var endIndex = 0;
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if (options.startIndex != null && options.endIndex != null) {
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startIndex = options.startIndex;
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endIndex = options.endIndex;
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}
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else if (options.startTime != null && options.endTime != null) {
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startIndex = this.at_time(options.startTime);
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endIndex = this.at_time(options.endTime);
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}
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if (startIndex < 0) {
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throw new RangeError("startIndex or startTime must not be negative");
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}
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if (endIndex < 0) {
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throw new RangeError("endIndex or endTime must not be negative");
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}
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if (startIndex > this.length) {
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startIndex = this.length;
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}
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if (endIndex > this.length) {
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endIndex = this.length;
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}
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if (startIndex > endIndex) {
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startIndex = endIndex;
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}
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var length = endIndex - startIndex;
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var header_size = 24; // Version 2
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var bytes_per_sample = this.bits === 8 ? 1 : 2;
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var total_size = header_size
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+ length * 2 * this.channels * bytes_per_sample;
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var output_data = new ArrayBuffer(total_size);
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var output_dataview = new DataView(output_data);
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output_dataview.setInt32(0, 2, true); // Version
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output_dataview.setUint32(4, this.bits === 8, true); // Is 8 bit?
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output_dataview.setInt32(8, this.sample_rate, true);
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output_dataview.setInt32(12, this.scale, true);
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output_dataview.setInt32(16, length, true);
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output_dataview.setInt32(20, this.channels, true);
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for (var i = 0; i < length * this.channels * 2; i++) {
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var sample = this._at(startIndex * this.channels * 2 + i);
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if (this.bits === 8) {
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output_dataview.setInt8(header_size + i, sample);
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}
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else {
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output_dataview.setInt16(header_size + i * 2, sample, true);
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}
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}
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return new WaveformData(output_data);
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},
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/**
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* Returns the data format version number.
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*/

‎test/unit/waveform-data.js‎

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Original file line numberDiff line numberDiff line change
@@ -55,7 +55,7 @@ export default function waveformDataTests(WaveformData) {
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context("with " + bits + "-bit " + format + " data", function() {
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beforeEach(function() {
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const data = format === "binary" ? getBinaryData({ channels: 1, bits: bits })
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: getJSONData({ channels: 1, bits: bits });
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: getJSONData({ channels: 1, bits: bits });
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instance = WaveformData.create(data);
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});
@@ -284,6 +284,96 @@ export default function waveformDataTests(WaveformData) {
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expect(result.duration).to.equal(expectations.duration * 3);
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});
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});
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describe(".slice()", function() {
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context("with valid startIndex and endIndex", function() {
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it("should return a subset of the waveform", function() {
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var extract = instance.slice({ startIndex: 1, endIndex: 4 });
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expect(extract.length).to.equal(3);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([-10, 0, -5]);
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expect(extract.channel(0).max_array()).to.deep.equal([10, 0, 7]);
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});
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});
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context("with endIndex beyond the length of the waveform", function() {
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it("should limit to the end of the waveform", function() {
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var extract = instance.slice({ startIndex: 1, endIndex: 12 });
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expect(extract.length).to.equal(9);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([-10, 0, -5, -5, 0, 0, 0, 0, -2]);
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expect(extract.channel(0).max_array()).to.deep.equal([10, 0, 7, 7, 0, 0, 0, 0, 2]);
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});
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});
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context("with startIndex equal to endIndex", function() {
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it("should return a zero length waveform", function() {
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var extract = instance.slice({ startIndex: 1, endIndex: 1 });
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expect(extract.length).to.equal(0);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([]);
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expect(extract.channel(0).max_array()).to.deep.equal([]);
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});
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});
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context("with startIndex greater than endIndex", function() {
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it("should return a zero length waveform", function() {
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var extract = instance.slice({ startIndex: 1, endIndex: 1 });
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expect(extract.length).to.equal(0);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([]);
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expect(extract.channel(0).max_array()).to.deep.equal([]);
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});
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});
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context("with startIndex and endIndex beyond the length of the waveform", function() {
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it("should return a zero length waveform", function() {
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var extract = instance.slice({ startIndex: 10, endIndex: 12 });
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expect(extract.length).to.equal(0);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([]);
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expect(extract.channel(0).max_array()).to.deep.equal([]);
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});
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});
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context("with negative startIndex", function() {
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it("should throw RangeError", function() {
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expect(function() {
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instance.slice({ startIndex: -1, endIndex: 4 });
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}).to.throw(RangeError);
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});
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});
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context("with negative endIndex", function() {
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it("should throw RangeError", function() {
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expect(function() {
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instance.slice({ startIndex: 1, endIndex: -1 });
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}).to.throw(RangeError);
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});
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});
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context("with valid startTime and endTime", function() {
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it("should return a subset of the waveform", function() {
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var extract = instance.slice({ startTime: instance.time(1), endTime: instance.time(4) });
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expect(extract.length).to.equal(3);
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expect(extract.channels).to.equal(instance.channels);
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expect(extract.bits).to.equal(instance.bits);
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expect(extract.channel(0).min_array()).to.deep.equal([-10, 0, -5]);
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expect(extract.channel(0).max_array()).to.deep.equal([10, 0, 7]);
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});
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});
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});
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});
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});
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});
@@ -295,7 +385,7 @@ export default function waveformDataTests(WaveformData) {
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context("with " + bits + "-bit " + format + " data", function() {
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beforeEach(function() {
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const data = format === "binary" ? getBinaryData({ channels: 2, bits: bits })
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: getJSONData({ channels: 2, bits: bits });
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: getJSONData({ channels: 2, bits: bits });
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instance = WaveformData.create(data);
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});

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