Volume control of MP3 files in QNX

We are trying to implement Volume Control Functionality using the mixer utility (amixer) available in QNX. We are able to dynamically control the Volume for TTS/WAV files. But the same does not work with MP3 Files.
The voume control commands that we send seem to work only after the MP3 track has completed playing.
I would like to know if anyone has faced a similar issue and whether they were able to resolve it.