I have a video which has a resolution of 1920x1080p. I want to re-encode this video (with libx264 for video and aac for audio); Downscale it first to 1280x720p (with the same aspect ratio) while using a different video bitrate (1900 kbps) and audio bitrate (96 kbps). Also I want to change from mkv to mp4. I don't want to change anything of the previous encoding settings (Just the bitrate, and the video size). I want to use variable bitrate (in video and audio), but I don't know how to put it in FFmpeg (I have the latest version 3.0- Windows 7). To get better quality, is it of any use to put a CRF value along with the variable bitrate (and if yes, how can I do that)? Also if I want to downscale it to 480p how can I do that and keep the aspect ratio intact?
One more thing; What is "maxrate", "minrate" and "bufsize" and where can I use these? I think I have seen that CRF uses VBR, but in one article the above were used (for VBR), so I can't tell exactly what to use to get a smaller file size by just decreasing the bitrate (and the video size, if possible).
Also I don't know if VBR mode is proper for the goal I want to achieve, but I have read it's the best mode.
Thank you for your time!