Update depreciated functions.

avcodec_free_frame  is deprecated, changed to av_frame_free
avcodec_alloc_frame deprecated, changed to av_frame_alloc


https://github.com/FFmpeg/FFmpeg/blob/0eec06ed8747923faa6a98e474f224d922dc487d/doc/APIchanges

2013-12-11 - 29c83d2 / b9fb59d,409a143 / 9431356,44967ab / d7b3ee9 - lavc 55.45.101 / 55.28.1 - avcodec.h
  av_frame_alloc(), av_frame_unref() and av_frame_free() now can and should be
  used instead of avcodec_alloc_frame(), avcodec_get_frame_defaults() and
  avcodec_free_frame() respectively. The latter three functions are deprecated.