Principal Web Developer at Freedom of the Press Foundation
Public
Edited
Apr 20, 2023
16 stars
fileBuffer = (await fetch(audioFile)).blob()
tags = new Promise(
(resolve, reject) => jsmediatags.read(
fileBuffer,
{ onSuccess: resolve, onError: reject }
)
)
context = createAudioContext()
audioBuffer = {
const buffer = await getFileArrayBuffer(fileBuffer)
return decodeAudioData(
context,
buffer
)
}
audioArray = audioBuffer.getChannelData(0)
chunkSize = nearestPowerOf2(audioBuffer.sampleRate / SAMPLES_PER_SECOND)
chunkCount = Math.floor(audioArray.length / chunkSize)
chromaBandCount = CHROMA_BANDS_PER_TONE * 12
chromaBandLabels = CHROMATIC_SCALE.reduce(
(acc, val, i) => {
acc[i * CHROMA_BANDS_PER_TONE] = val
return acc
}, {}
)
chroma = {
let returnVal = new Array(chunkCount)
Meyda.chromaBands = chromaBandCount
for (const i of R.range(0, chunkCount)) {
const features = Meyda.extract(
'chroma',
audioArray.slice(i * chunkSize, (i + 1) * chunkSize)
)
returnVal[i] = {
startTime: msForSample(i * chunkSize),
chroma: features,
}
yield returnVal
}
}
height = width / 2
margin = ({ top: 20, right: 20, bottom: 30, left: 30 })
xScale = d3.scaleBand()
.domain(R.range(0, chunkCount).map(i => msForSample(i * chunkSize)))
.range([
margin.left,
width - margin.right
])
xScaleContinuous = d3.scaleLinear()
.domain([0, msForSample(audioBuffer.length)])
.range([
margin.left,
width - margin.right
])
yScale = {
const bands = R.range(0, CHROMA_BANDS_PER_TONE * 12)
// Rotate the bands array to get all the
// bands close to C on the bottom of the graph
// (otherwise Pure C will be the bottom of the graph
// and some close to C bands will be on top)
const rotationCount = Math.floor(CHROMA_BANDS_PER_TONE / 2)
bands.unshift.apply(bands, bands.splice(bands.length - rotationCount, rotationCount))
return d3.scaleBand()
.domain(bands)
.range([
height - margin.bottom,
margin.top
])
}
xAxis = g => g.attr('transform', `translate(0, ${height - margin.bottom})`)
.call(
d3.axisBottom(xScale)
// TODO: Figure out a good way to add final tick. We may need to switch from scaleBand to scaleTime
.tickValues([0])
.tickFormat(formatDuration)
)
yAxis = g => g.attr('transform', `translate(${margin.left}, 0)`)
.call(
d3.axisLeft(yScale)
.tickValues(
Object.entries(chromaBandLabels).map(x => x[0])
)
.tickFormat(t => chromaBandLabels[t])
)
colorScale = d3.scalePow().exponent(CONTRAST).range(COLOR_SCALE).domain([0, 1])
AudioPlayerMonitor = class {
constructor(audio, monitorFn) {
this._audio = audio
this._monitorFn = monitorFn
this.startMonitoring = this.startMonitoring.bind(this)
this.stopMonitoring = this.stopMonitoring.bind(this)
this.tick = this.tick.bind(this)
audio.addEventListener('play', this.startMonitoring)
audio.addEventListener('pause', this.stopMonitoring)
audio.addEventListener('seeked', () => this.tick(false))
// If the audio is currently playing, start monitoring!
if (!this._audio.paused) this.startMonitoring()
}
startMonitoring() {
this.tick()
}
stopMonitoring() {
cancelAnimationFrame(this._nextFrame)
}
tick(requestNextFrame = true) {
this._monitorFn(this._audio)
if (requestNextFrame) this._nextFrame = requestAnimationFrame(this.tick)
}
}
nearestPowerOf2 = n => {
return Math.pow(2, Math.round(Math.log(n) / Math.log(2)));
}
msForSample = hz => hz * 1000 / audioBuffer.sampleRate
formatDuration = ms => {
const secondsTotal = Math.floor(ms / 1000)
const hours = Math.floor(secondsTotal / 3600)
const minutes = Math.floor((secondsTotal % 3600) / 60)
const seconds = secondsTotal % 60
if (hours) return [hours, minutes, seconds].join(':')
return [minutes, seconds].join(':')
}
createAudioContext = () => {
try {
return new AudioContext()
} catch {
// Safari
return new window.webkitAudioContext()
}
}
getFileArrayBuffer = async blob => {
try {
return await blob.arrayBuffer()
} catch {
// Safari
const reader = new FileReader()
reader.readAsArrayBuffer(blob)
return new Promise((resolve, reject) => {
reader.addEventListener('loadend', e => resolve(e.target.result))
})
}
}
decodeAudioData = async (context, arrayBuffer) => {
try {
return await context.decodeAudioData(arrayBuffer)
} catch {
// Safari
return new Promise((reject, resolve) => {
context.decodeAudioData(arrayBuffer, reject, resolve)
})
}
}
COLOR_SCALE = DARK_MODE ? ['#050A0F', '#CEF'] : ['#FAFCFF','#101C20']
PLAY_HEAD_COLOR = DARK_MODE ? '#A80' : 'rgba(0, 100, 150, 1)'
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