Describe the bug
If ffmpeg doesn't include enable-librubberband, then transposition doesn't work, and it will hang the app.

To Reproduce
Use pikaraoke on any machine with a version of ffmpeg lacking in librubberband. You can check by running ffmpeg on the command line and noting the absense of "--enable-librubberband" in the output under "configuration:"

Most recent versions of ffmpeg include librubberband, but we recently found that Android + termux ffmpeg 6.1 package doesn't

Expected behavior
Pikaraoke should warn the user in logging and disable the transposition feature.

Platform (please complete the following information):

• Hardware: Android
• OS: Android OS / Termux linux runtime
• OS version: 8.0
• Browser: N/A
• Version: N/A