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# Custom Audio Player

**Date:** October 2025
**Technologies:** TypeScript, React

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## Project Overview

The Custom Audio Player is a self-contained React component that renders inside the site's markdown pipeline, turning `<audioplayer url="...">` tags into rich, interactive embeds. It is used in some blog entries in the GDGoC UAM blog, like [this one about Magenta.js](https://gdguam.es/blog/evento-de-bienvenida), our first ever event.

Unlike a standard HTML5 `<audio>` element, this player renders a pre-computed waveform as a bar chart on a high-DPI canvas, supports click-and-drag seeking across the full timeline, and adapts its bar density automatically between desktop and mobile viewports.

## Technical Architecture

### Pre-Computed RMS Waveform

Rather than using `AnalyserNode` for real-time frequency data (which produces fluctuating visuals that change on every playthrough) the component decodes the entire audio file into an `AudioBuffer` and computes per-segment RMS (Root Mean Square) values once at load time.

This produces a stable, deterministic waveform where each bar's height is fixed to the actual amplitude envelope of the recording. The result is cached in component state and never recomputed, keeping the animation loop lightweight.

### Canvas Rendering Loop

The waveform draws via `requestAnimationFrame` on a canvas scaled to `window.devicePixelRatio` for crisp edges on Retina displays. Each bar is a rounded rectangle constructed manually with `quadraticCurveTo` to avoid CSS border-radius overhead inside a tight animation loop.

The renderer distinguishes three visual states:

- **Future segments**: Light gray (`#e2e8f0`)
- **Past segments**: Medium gray (`#94a3b8`)
- **Current segment**: Brand blue (`#1a73e8`)

Bar dimensions are recalculated on every frame based on the container's live width, which is observed via `ResizeObserver`. On mobile (detected at `max-width: 640px`), the component switches to a lower bar count to prevent visual crowding.

<div style="max-width: 600px; margin: 0 auto;">

![Screenshot from the GDG UAM blog (Magenta.js event).](/assets/projects/gdguam/website/custom-markdown/audio-player/player.webp)

</div>

## Interaction Design

### Pointer-Driven Seeking

The entire canvas surface acts as a scrubbing control. The component differentiates between a **click** (seek to position) and a **drag** (scrub while paused) using distance and time thresholds:

- `MOVE_THRESHOLD = 6px`
- `HOLD_THRESHOLD = 100ms`

If the user drags while audio is playing, playback enters a temporary pause state so the waveform stays synchronized with the pointer, then resumes automatically on release.

### Responsive Bar Density

The component accepts independent `bars` and `mobileBars` props. At mount and on `resize`/`orientationchange`, it tests `window.matchMedia("(max-width: 640px)")` to decide which density to use. This ensures desktop users see a detailed waveform while phone users get a readable, uncluttered timeline.

### Accessibility and Fallbacks

- The play/pause button is a native `<button>` with clear `aria-label` support inherited from the parent markdown renderer.
- If audio decoding fails or the fetch returns a non-200 status, the component enters an error state that disables controls and surfaces a console warning.
- A loading spinner overlays the play button while the `ArrayBuffer` is being fetched and decoded.