2 identical pieces of audio are out of sync

I am an Animate newbie so there may be a very obvious feature I'm missing, but I imported a .mp4 video for use as animation reference, and then converted the audio from that video to an mp3 to layer under my animation. However, while the audio in the mp4 video syncs up perfectly with my animation, the audio track I import is always out of sync. It starts at the same time, and I've tried adjusting the starting point to fit better, but it always ends up out of sync in a matter of seconds. What is going on?