Gradio will timeout after 5s and show "Error" as if backend works

Clicking `Convert` shows "Error" in the WebUI when the process take longer than 5s.

## Reproduction
- Use longer audio(such as 483s) file for inference

Related Issue: #2714, #160, #2605, #2627, #2394, #2158, #2379 

## Fix PR
#2818 