Regex error for base64 audio

**Describe the bug**

This regex here doesn't match my base64 audio: https://github.com/ffmpegwasm/ffmpeg.wasm/blob/d76b5ede25c4c6d02411113060b1c2aeb3b47939/src/node/fetchFile.js#L21

**To Reproduce**
Steps to reproduce the behavior:
1. Go to https://regexr.com/5vrf8
2. Notice that the regex doesn't match the base64 URL

**Expected behavior**

I expected to be able to pass a base64 encoded audio string to fetchFile in node.

**Desktop (please complete the following information):**
- OS: [e.g. iOS] N/A
- Browser [e.g. chrome, safari] N/A
- Version [e.g. 22] N/A

**Additional context**

I'm trying to concatenate files together and they're encoded as base64 so I'd like to be able to pass them as-is. Also, I'm probably missing something because I don't think there's any normal base64 string that would match that regex.