So.. I have a buffer with MP3 data (If I would save this buffer and call it buffer.mp3 it would play, but in this situation I should not save it to file system)
This one doesn't work since SampleDataEvent.data expects uncompressed raw sample data, not MP3. Use https://github.com/claus/as3swf/wiki/play-mp3-directly-from-bytearray instead.