Fixed call to av_buffersrc_add_frame
Removed const cast for swr_convert call
Revert "Removed TARGET_LINUX needed for types/defines in PlatformDefs (may interfere with openFrameworks TARGET_LINUX if defined on gcc command line, but the defs are needed)"

This reverts commit cd3bc6aaa44d7f60575de6d60ffdf37e9125cee8.
Replaced TARGET_ defines with OMXPLAYER_TARGET_ defines to avoid collision with openFrameworks TARGET_ defines