Upload an audio file or a video file can a be a problem if your server has a low upload maximum size limit. (e.g 4M).
Here is a way to work around this.
Use the following tip if you need to increase the upload_max_filesize on your web server, especially if you are not able to directly access/edit the php.ini file.
1. Create a new file and name it php.ini (the name and the extension are very important).
2. Open it with any text editor and paste the following lines:
upload_max_filesize = 40M post_max_size = 40M
3/ Then, save the file and upload it into your wp-admin folder.
Tested on 1&1 and Bluehost.
If it doesn’t work, contact your hosting provider.
Additionally, you can check this post to find more ways to increase your max upload size.