Generate base64 waveform in audio message body

src/components/messages/AudioPlayer.vue

@@ -6,15 +6,22 @@
     <div class="play-time">
       {{ currentTime }} / {{ totalTime }}
     </div>
+    <div style="position:relative;flex: 1 1 100%">
     <v-slider @change="seeked" :disabled="!info.url" color="currentColor" track-color="#cccccc" class="play-progress" :value="info.playPercent" min="0"
       max="100" />
+      <div style="position:absolute;left:18px;right:18px;top:0;bottom:0;height:100%">
+      <AudioWaveformView :event="event" style="width:100%;height:100%" />
+      </div>
+    </div>
   </div>
 </template>
 
 <script>
 import util from "../../plugins/utils";
+import AudioWaveformView from "./AudioWaveformView.vue";
 
 export default {
+  components: { AudioWaveformView },
   props: {
     event: {
       type: Object,

src/components/messages/AudioWaveformView.vue

@@ -0,0 +1,79 @@
+<template>
+    <canvas ref="waveform">
+    </canvas>
+</template>
+
+<script>
+//  import util from "../../plugins/utils";
+
+export default {
+    props: {
+        event: {
+            type: Object,
+            default: function () {
+                return null;
+            },
+        },
+    },
+    data() {
+        return {
+        };
+    },
+    mounted() {
+        this.drawWaveform(this.event);
+    },
+    methods: {
+        drawWaveform(event) {
+            const canvas = this.$refs.waveform;
+            if (canvas) {
+                const dpr = window.devicePixelRatio || 1;
+                canvas.width = canvas.offsetWidth * dpr;
+                canvas.height = (canvas.offsetHeight) * dpr;
+
+                const ctx = canvas.getContext("2d");
+
+                ctx.clearRect(0, 0, canvas.width, canvas.height);
+
+                const base64content = event ? event.getContent().formatted_body : undefined;
+                if (base64content) {
+                    const data = atob(base64content).split('').map(function (c) { return c.charCodeAt(0); });
+
+                    const drawLineSegment = (ctx, x, y0, data) => {
+                        ctx.lineWidth = 1; // how thick the line is
+                        ctx.strokeStyle = "#000"; // what color our line is
+                        ctx.beginPath();
+                        ctx.moveTo(x, y0 - data);
+                        ctx.lineTo(x, y0 + data);
+                        ctx.stroke();
+                    };
+
+                    console.log("W", canvas.width, canvas.height, canvas.offsetWidth, canvas.offsetHeight);
+
+                    const width = canvas.width;
+                    const height = canvas.height;
+                    const samples = data.length;
+                    for (let i = 0; i < width; i++) {
+                        if (i % 4 == 2 || i % 4 == 3) continue;
+                        const iSample = Math.floor(width == 0 ? 0 :(1000 * i) / width);
+                        const sample = iSample < samples ? data[iSample] : 0;
+                        drawLineSegment(ctx, i, height/2, (sample / 255) * height / 2);
+                    }
+                }
+            }
+
+        }
+    },
+    watch: {
+        event: {
+            immediate: false,
+            handler(event) {
+                this.drawWaveform(event);
+            }
+        }
+    }
+};
+</script>
+
+<style lang="scss">
+@import "@/assets/css/chat.scss";
+</style>

src/plugins/utils.js

@@ -424,6 +424,9 @@ class Util {
                     promise
                         .then((response) => {
                             messageContent.url = response.content_uri;
+                            return (msgtype == 'm.audio' ? this.generateWaveform(fileContents, messageContent) : true);
+                        })
+                        .then(() => {
                             return this.sendMessage(matrixClient, roomId, "m.room.message", messageContent)
                         })
                         .then(result => {
@@ -478,6 +481,9 @@ class Util {
                             return reject(response.error);
                         }
                         encryptedFile.url = response.content_uri;
+                        return (msgtype == 'm.audio' ? this.generateWaveform(fileContents, messageContent) : true);
+                    })
+                    .then(() => {
                         return this.sendMessage(matrixClient, roomId, "m.room.message", messageContent)
                     })
                     .then(result => {
@@ -495,6 +501,39 @@ class Util {
         return uploadPromise;
     }
 
+    generateWaveform(data, messageContent) {
+        const audioCtx = new (window.AudioContext || window.webkitAudioContext)();
+        if (audioCtx) {
+            return audioCtx.decodeAudioData(data)
+                .then((audioBuffer) => {
+                    const rawData = audioBuffer.getChannelData(0); // We only need to work with one channel of data
+                    const samples = 1000; // Number of samples we want to have in our final data set
+                    const blockSize = Math.floor(rawData.length / samples); // the number of samples in each subdivision
+                    let filteredData = [];
+                    for (let i = 0; i < samples; i++) {
+                      let blockStart = blockSize * i; // the location of the first sample in the block
+                      let sum = 0;
+                      for (let j = 0; j < blockSize; j++) {
+                        sum = sum + Math.abs(rawData[blockStart + j]) // find the sum of all the samples in the block
+                      }
+                      filteredData.push(sum / blockSize); // divide the sum by the block size to get the average
+                    }
+
+                    // Normalize
+                    const multiplier = Math.pow(Math.max(...filteredData), -1);
+                    filteredData = filteredData.map(n => n * multiplier);
+
+                    // Integerize
+                    filteredData = filteredData.map(n => parseInt((n * 255).toFixed()));
+                    
+                    const base64 = Buffer.from(filteredData).toString('base64'); //.replace(/=/g, '')
+                    console.log("BASE64", base64);
+                    messageContent.format = "org.matrix.custom.html";
+                    messageContent.formatted_body = base64;
+                })
+        }
+    }
+
     /**
      * Return what "mode" to use for the given room.
      *