Frame Rate - PAL is 25 fps, NTSC is 29.97 fps (Not 30), film is 24. If you want to cut frame rate some people will cut it in half. Many newbie compressionists think cutting the frame rate in half cuts the file size in half. It will cut the size but not in half.
Encoders make important decisions about throwing out data based on how much different one frame is compared to the next. It needs to keep more data to keep up a level of quality if the frames are very different. The more similarity from frame to frame the more it can throw out duplicate data. Well, lower frame rate means greater difference from frame to frame so it doesn't throw out as much data as some would think. In short, cutting the frame rate in half won't cut the file size in half
When referring to audio, bitrate is a measurement of bits each second that audio distributes. The sound quality will improve as the bitrate improves.