Safari 17: Gets stuck when trying to convert video to png sequence in Multi-thread mode

**Describe the bug**
When using Safari 17, trying to convert a video to a png sequence in multi-threaded mode, it gets stuck before finishing

**To Reproduce**

1. Open the browser 'Safari' version 17
2. Open https://ffmpegwasm.netlify.app/playground/
3. Click 'Use multi-threading'
4. Click 'Load sample files'
5. Enter the following arguments:
```
[
"-i",
"video.webm",
"frame%04d.png"
]
```
6. Observe the log. It gets stuck at 'video:40913kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown'

**Expected behavior**
Should complete the transcoding and output the png sequence in the virtual file system.

**Screenshots**

**Desktop (please complete the following information):**
- OS: macOS Sonoma
- Browser: Safari
- Version: 17

**Additional context**
It works fine when converting to video. It works for converting to png sequence if **not** in multi-threaded mode. Multi-threaded mode seems to be causing issues everywhere as it doesn't work at all (not even video to video conversion) in Chromium-based browsers as noted in #597.