A lightning-fast, purely client-side Dual-Tone Multi-Frequency (DTMF) telemetry analyzer. Built entirely with HTML, CSS, and Vanilla JavaScript, this tool extracts and decodes dial-pad tones directly from audio and video files without ever sending your data to a server.
| Feature | Description |
|---|---|
| 🎬 Universal Media Support | Upload standard audio (.mp3, .wav) or extract audio layers directly from video files (.mp4, .mkv) instantly. |
| ⚡ Zero-Server Processing | Everything happens in your browser. No uploads, no backend, 100% private and offline capable. |
| 🎚️ Smart Normalization | Automatically boosts quiet signals to ensure accurate detection even in poorly recorded media. |
| 💾 Persistent Terminal | An integrated analysis console that saves your session history locally until you explicitly clear it. |
| 📱 Responsive UI | A lightweight, "calm blue" interface perfectly scaled for small screens and low-DPI displays. |
This tool doesn't just guess; it uses deep signal processing mathematics to find hidden tones. Here is the humanistic breakdown of what happens under the hood when you upload a file.
The Prep-Work: When you load a file, the browser's native
AudioContextAPI intercepts the media. If it's a video, it effortlessly strips away the visual data and grabs just the raw audio waveform, decoding it into raw mathematical samples.
The Heavy Lifting: Instead of running a massive, CPU-heavy Fast Fourier Transform (FFT) to map every sound in the file, we use the Goertzel Algorithm. It acts like a highly tuned laser, ignoring background noise and searching only for the 8 specific frequencies used in DTMF telecom standards.
The Bouncer: Just finding a frequency isn't enough. Human voices can sometimes mimic these tones. The analyzer applies strict Twist Checks—ensuring the "high" tone and "low" tone hit at the exact same time with similar energy levels. If the signal doesn't pass the threshold, it is dismissed as background noise.
For the curious, here is the matrix our algorithm hunts for. A valid button press must contain exactly one Row frequency and one Column frequency:
| High Frequencies ➔ | 1209 Hz |
1336 Hz |
1477 Hz |
1633 Hz |
|---|---|---|---|---|
Low 697 Hz |
1 | 2 | 3 | A |
Low 770 Hz |
4 | 5 | 6 | B |
Low 852 Hz |
7 | 8 | 9 | C |
Low 941 Hz |
* | 0 | # | D |
Because this is a standalone Single-Page Application (SPA), installation is delightfully simple:
- Clone or download this repository.
- Open
Decoderpro.htmldirectly in any modern web browser (Chrome, Edge, Firefox, Safari). - Select your scan duration (e.g., First 30 seconds, 60 seconds, or Custom).
- Click Upload Media and select your file.
- Watch the real-time decoding in the terminal!
- Custom Scan Length: Use the "Custom" dropdown option to specify exact seconds to save memory on massive files.
- Whole File Scan: Use the "Whole File" option carefully on files larger than 10 minutes, as your browser will need to chew through millions of audio samples.
- Structure: HTML5
- Styling: CSS3 (Custom Calm-Blue Theme)
- Logic: Vanilla JavaScript (ES6)
- APIs: Web Audio API, LocalStorage API
Designed and engineered for ultra-responsive, secure, client-side execution.