Set the minimum required version of libavcodec to 51.12.0. I am not sure if this is the true minimum, but I do know that our FFmpeg code does not compile with version 51.7.0.
Set the minimum required version of libavcodec to 51.12.0. I am not sure if
this is the true minimum, but I do know that our FFmpeg code does not
compile with version 51.7.0.

patrickhartling/vrkit,patrickhartling/vrkit,patrickhartling/vrkit