The file downloaded, the player shows progress, but silence. Work through these causes in order; the first two resolve most cases.
Check: play the YouTube video itself. Some uploads have muted audio tracks (copyright-muted sections or silent videos). Fix: if the source has no audio, no converter can create any. Find an upload with sound.
Check: look at the file size. A normal 4-minute song is several megabytes. A file of a few kilobytes is empty: the conversion failed silently. Fix: delete it and convert again. If it keeps producing empty files for one video, see why won't my video convert.
Check: on phones and computers, audio can route to a forgotten Bluetooth device. Fix: disconnect Bluetooth or switch output to the phone/computer speaker, then replay.
Check: try the file in VLC or another app. Fix: if it plays in VLC but not your default player, the default player's cache or codec handling is at fault. Clear the app cache or keep using the player that works. If the file won't play anywhere, that is a different problem.
Check: media volume (not ring volume) on phones, per-app volume on desktops, and any mute toggle in the player. Fix: embarrassingly common, quickly ruled out.
Check: compare the file size against expectations (about 1MB per minute at 128kbps). A much smaller file stopped mid-download. Fix: re-download on a stable connection. See download keeps failing if it recurs.
Different symptom? Return to the troubleshooting hub.
The usual causes are a muted or silent source video, a failed stream fetch that produced an empty file, a player glitch, or audio routing to the wrong output device. Check the file size first.
Check the size: a normal song is several megabytes, while a few kilobytes means the file is empty. Also try playing it in VLC.