Video bitrate means the number of bits encoded into the video. 1 byte = 8 bits and the more bits equals more quality but that also means a bigger file size. If you have a video that had a data rate of 2 megabytes per second this would be 16 megabits (mbps) per second in bitrate. You can also have kilobytes video rate and kilobits bitrate.
A good guide on what bitrate to use for what video dimension and frame rate is this YouTube post.
As you can see the less pixels (video dimension) like 360p the less bitrate you need. But for high pixel videos like 4k you obviously need a lot more data to be shown in these videos so the bitrate is very high. When editing a video there is no benefit to setting the encode bitrate to one higher than what the source bitrate is.
The difference in bitrate needed for the video frame rate essentially comes down to the more frames per second (fps) the more frames that will be shown! A video in 60fps is going to have more frames than the same one in 30fps.
CBR and VBR
Now onto the two types of bitrate encoding: Constant bitrate encoding (CBR) and Variable bitrate encoding (VBR). Constant bitrate encoding keeps the same bitrate amount for the whole video, if you have scenes that show a blank wall or have little movement and detail it will still apply your set bitrate even though this will be a lot higher than needed for these scenes.
Variable bitrate gives higher bitrate to complex scenes or scenes with great detail and allocates smaller bitrate amounts to the scenes as described above that do not need great detail. This gives an average bitrate level to the file and its usually close to what a CBR bitrate would achieve. VBR takes longer than CBR to encode.
Given that VBR takes longer and uses a greater amount of CPU it is CBR that is favored by live streamers like on the platform Twitch.
1 pass or 2 pass?
2 pass encoding is when the first phase of an encode a log file gets generated with the videos data and then on the second phase (second pass) the video gets encoded with bitrate levels calculated from the generated file. 2 Pass is quite slow, especially 2 pass VBR but the quality is greatest. However your video is going to be uploaded to YouTube and viewed in no other way don’t bother with 2 pass, the benefits will be minimal to none when viewed from YouTube.