Audio file extension containing capital letters may cause errors at export

[Picorims]

Describe the bug
Using audio extensions that have capital letters in it can cause issues at export.

To Reproduce
Steps to reproduce the behavior:

1. Import an audio file with an extension containing capital letters.
2. Try to export the video.

Expected behavior
The video exports successfully.

Desktop (please complete the following information):

• OS: Windows 10
• Version: beta-0.3.0

Additional context
Using extensions without any capital letters (like .wav instead of .Wav or .WAV) is a workaround to the issue.