Function ffmpeg_path

pub fn ffmpeg_path() -> PathBuf

Returns the default path of the FFmpeg executable, to be used as the argument to Command::new. It should first attempt to locate an FFmpeg binary adjacent to the Rust executable. If that fails, it should invoke ffmpeg expecting it to be in the system path. If that fails, an informative error message should be printed (not when this function is called, but when the command is actually run).