How to re-encode file A.mp4 with the same settings as B.mp4?

I have a MP4 file with AAC audio and H264 video, let's call it B.mp4. I also have file A.mp4 with the same picture resolution, but: - different FPS - possibly different audio/video bitrate - different codecs I would like to re-encode file A.mp4 with the exact same settings as B.mp4 because after that I want to use mkvmerge to mux them together, so they must match. How can I do this? Is there a way to "copy" settings from B.mp4 to A.mp4? Up to now I am able to see some codec information using mediainfo or mplayer -identify, but I don't know how to pass everything to ffmpeg (preferably) or mencoder. The command I am looking for should copy every setting (codec, bitrate, frame rate, ...) from one video to the re-encoded version of the other one. Even better if I can specify starting and ending keyframes on video A.mp4.