Limitations on Using MMAPI in the Toolkit
Keep in mind that the J2ME Wireless Toolkit has the following limitations � and that every device will have its own, different limitations:
-An application can create multiple players, but can realize only one MIDI player or one tone-sequence player. Any attempt to realize a second player of either type will throw a MediaException. In other words, only one MIDI or tone sequence player can be in use at any time.
-The toolkit allows any number of simultaneous playTone() calls for a single note, but guarantees only that at least four will actually work. The playTone() method can be called while a MIDI or tone-sequence player is playing.
-The number of video players is limited by the size of the heap, as specified in the -Xheapsize option of the emulator command if you are using the command line utilities, or from KToolBar by choosing Edit -> Preferences -> Storage.
-The number of WAV audio players is also limited by the heap size.
-Only one audio capture can be in use at one time.
Here is the link to the article, u might want to read to gain some knowledge about developing the multimedia applications with J2ME...