BFRAME_PRE
case BFRAME_PRE:
framelen[1] = mpeg1_frame_header(go, buf + i, 0, 1, BFRAME_PRE);
0, 2, BFRAME_PRE);
case BFRAME_PRE:
framelen[1] = mpeg4_frame_header(go, buf + i, 0, BFRAME_PRE);
framelen[5] = mpeg4_frame_header(go, buf + i, 1, BFRAME_PRE);