title: “INVALID FILE NAME: MUST CONTAIN ONLY [a-z0-9_.]“ for sound files in Android Studio
body: <p>I am creating an Android App that has sound files in the <code>res/raw</code> folder. 50 of them. They are all named <code>s1.mp3</code>, <code>s2.mp3</code>, <code>s3.mp3</code> etc.</p>
  
  <p>I have done some searches and found that everyone getting this error only gets it because their file has a capital letter in it. Mine doesn't.</p>
  
  <p>The error started by specifically pointing out that <code>s37.mp3</code> had the incorrect file name. I then moved that file away completely, thinking that it had a bug or something. When I tried to recompile, it said <code>s38.mp3</code> had the problem. I then moved all files after <code>s36.mp3</code> away and it then pointed to <code>s12.mp3</code> as the problem.</p>
  
  <p>So obviously the Android Studio sees a problem with all of the sound files' names. When I look at the navigation bar on the left of the screen, I see that all the sound files have their regular names, but their extensions are in caps (.MP3). Of course this cannot be the problem, right?</p>
  
  <p><a href="https://i.stack.imgur.com/yjsRG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yjsRG.png" alt=""></a></p>