Please note that the 1080p bit per pixel density shown below is post encode and is not the source file. Using the matrix below, assuming you do not want to make one of your own, you should be able to find an approximate bitrate to use for your other resolutions. If you run a one minute CRF encode against each minute in your source 1080p video you will be provided with a bit per pixel density matrix. I did some work and came up with some data. To retain a relatively sane visual quality, the lower the resolution of the video the higher the bit per pixel density should be. From that I validated a trend that I had been seeing for a while. As expected this yielded a fair amount of data as each one minute section of the source video I encoded was different. Once I figured out how to perform single pass ABR encoding I decided to perform some ABR encoding using CRF 21 to find an approximate bit per pixel density. Desperation, being the mother of invention, decided to intervene on my behalf. The problem with doing that is that every source video is different, even throughout the entire video, and I did not want to encode multiple different video files multiple times to generate this matrix.

I remembered that statement when I wanted to calculate a bit per pixel density encoding matrix for different video resolutions. I was once informed that it would be nigh impossible to create ABR content in one pass using FFmpeg.

Ffmpeg scale video to 720p