Some parts of the code are based on a patch by Timo Rothenpieler <timo@rothenpieler.org> Merges Libav commit b9129ec4668c511e0a79e25c6f25d748cee172c9. Due to the name clash with our cuvid decoder, rename it to nvdec. This commit also changes the Libav code to dynamic loading of the cuda/cuvid libraries. Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>