MP4s, AACs, and WMAs uses too much CPU usage than MP3s

[freelancerage]

This is very noticeable even in other media players (I tested different media players (popular or not) provided that it only uses the minimum installation, CPU and memory usage).
Using older machines this could be very noticeable.

Playing MP3 type audios doesn't degrade system performance that much. Even you open up more applications, the playback doesn't stop for a while (this is also applicable even you lower the mp3 plugin priority into "Higher" level [default: "Highest"])

On MP4s, AACs, and WMAs it's the other way around. A move of your mouse or even opening up Windows Explorer stops the playback for a while or even degrades the system performance too much.

What is the basis of this..is it on the development of the "audio container" or the plugin the decodes the audio?