You could approximate this on <canvas> by drawing on multiple overlapping canvases: on every frame 1) clear the primary canvas and draw the waveform on it, 2) c

You could approximate this on <canvas> by drawing on multiple overlapping canvases: on every frame 1) clear the primary canvas and draw the waveform on it, 2) clear the secondaries with rgb(0,0,0,0.3) as the fill color (decrease the alpha for bigger blurs), 3) draw the primary on the secondaries. Apply additive blend mode and blur filters in CSS to the secondaries. It’s not the most elegant solution, but more simple than drawing on one canvas.