I am just getting the ropes of Animate, and one of the problems I've had with it is a very finicky audio import system. All of the time, it will accept .WAV files. However, if I include a piece of .MP3 audio from Audacity, it opens a dialogue box stating that it couldn't import the audio. I've tried changing bit rates, checked the properties of the audio files, changed audio channels, and rates of the audio (Fast, medium, etc.). I never got consistent results. And yet, when I record a 1-second piece of audio of me saying a single word, "Hi"(Under the same parameters), it imports! I don't understand what is my mistake,if it is my own fault at all, and i can't even seem to find anyone with the same problem as me, either on these forums or even the internet.
So save it as a WAV file and import it.
You didn't mention if this is AS3 or Canvas. In general MP3 is better for Canvas, and WAV is better for AS3. In either case, don't import 24 or 32 bit audio, just use 16 bit. Also 44.1 kHz is better, to avoid some other sync issues.
I tried using my audio at 160 kb with 44.1 kHz, and it totally worked! This problem was bugging me for weeks. Thanks Man!