To convert audio from a URL to base64 and then play it using Audio5js in JavaScript, you can follow these steps:

1. Fetch the audio file from the URL.
2. Convert the fetched audio to a base64 string.
3. Use Audio5js to create an audio element and play the base64-encoded audio.

Here's a basic example using JavaScript:

```javascript
// Function to fetch audio from URL and convert it to base64
async function fetchAndPlayAudio(url) {
  try {
    const response = await fetch(url);
    const audioBlob = await response.blob();

    const reader = new FileReader();
    reader.readAsDataURL(audioBlob);
    reader.onloadend = function () {
      const base64data = reader.result.split(',')[1]; // Extract base64 data
      playAudioUsingAudio5js(base64data);
    };
  } catch (error) {
    console.error('Error fetching or playing audio:', error);
  }
}

// Function to play audio using Audio5js
function playAudioUsingAudio5js(base64data) {
  var audio = new Audio5js({
    formats: ['mp3', 'ogg', 'wav'],
    autoplay: true,
    loop: false,
    ready: function () {
      this.load('data:audio/mp3;base64,' + base64data); // Change mime type accordingly
      this.play();
    }
  });
}

// Example usage:
const audioURL = 'YOUR_AUDIO_URL_HERE';
fetchAndPlayAudio(audioURL);
```

Replace `'YOUR_AUDIO_URL_HERE'` with the actual URL of the audio file you want to play. This code fetches the audio file from the given URL, converts it to base64, and then uses Audio5js to play the audio using the generated base64 data.

Remember, this is a simplified example. Depending on the browser's security policies, you might face restrictions when attempting to fetch audio from some URLs due to CORS (Cross-Origin Resource Sharing) policies.