Usage:

1. FGS
vm_dec -fgs fgsbitstream_file base_layer_bitstream_file output_file width height

2. FGST
vm_dec base_layer_bitstream_file enhn_layer_bitstream_file output_file width height

3. FGS-FGST
vm_dec -fgs fgsbitstream_file base_layer_bitstream_file enhn_layer_bitstream_file output_file width height
