Who Am I - .mp3 format can be converted into various other .mp3 format levels. The bitrate can be brought down, allowing for smaller files at the expense of quality of playback.
For example, I read some bodybuilding articles into a digital recorder over a period of time and wanted to squeeze them all onto one CD. As they were, I could only fit 20 articles onto one CD.
I opened the .mp3 files and used
Audacity to lower the bitrate so I could fit more onto one CD. When I was done, I fit 80 articles onto one CD with room to spare.
I don't know of any other formats that would squeeze all that playtime onto one CD. .wav would be too long, I'd think.
The thing with lower bitrates and the new Windows MediaPlayer is that it won't play back correctly. Sometimes it'll sound all chipmunky and makes me want to rush out and paint my toenails.
How old is your computer?