Fix for compiler warnings and deprecated functions usage in videoplayer.

Fix for compiler warnings and deprecated functions usage in videoplayer.

Deprecated functions were:
- AVCodecContext::get_buffer
- AVCodecContext::release_buffer

Changed to:
AVCodecContext::get_buffer2 and setting AVCodecContext::refcounted_frames to 1
before call to avcodec_open2(), and release_buffer usage was removed.

Also changed places when some fileds were compared to AV_NOPTS_VALUE
- it's signed, so removed unsigned int casting, or changed casting
to signed int.

Signed-off-by: Lukasz Gromanowski <lgromanowski@gmail.com>