I have not tried this in OS 9 or even knows if it is possible, but I have been taking my .mp4 video files and stripping out the audio to a AIFF file. I normally download 720p or 1080p video files so that the audio portion is good to convert to AIFF. Since my mode of transportation does not support mp3 format, I am stuck with Audio CDs.
One of my favorite rock films, Pink Floyd - Live at Pompeii - Directors Cut - Full Length_ .mp4, I converted to a AIFF file to split into 2 CDs.
The .mp4 file is 1.4GB. It sits on my Western Digital My Passport external HD USB3/2. While in OS 10.4.6, I can run Audacity 2.0.5, which allows me to import .mp4 files. To export a AIFF file back to the same HD, it took 5:38 min/sec. Since I don't have a G4 setup with the same Audacity software, is this O.K. or is it slowwww.