Can anybody let me know how to find diff between MPEG1 and MPEG2 Layer III bitstreams? What if MPEG2 Layer III bit stream is fed into MPEG1 Layer III decoder?

The internal bitstream struture is the same.. Only there is some differences in the header to mark the lower sampling rate of MPEG2..

Naturally a MPEG1 layer III cannot decode MPEG2 layer III and vice verse.. However, a fully conforming MP3 player should be able to decode both MPEG1 & MPEG2 layer III.

Also MPEG2 LayerIII has only 1 granule per frame.