I suspect its the video files that are in MPEG form the sound files are likely to be MP3 I guess - anyway that's my set up when I make VCDs.
It's very hard to guess what might be wrong because there are all sorts of potential causes
- are your music files MP3/
- are you using Nero to burn them if so what
- what speed are you burning your disc at
- how confident are you about your video/audio capture programme.
Post back the answers to these for atarters