I have some 720p 30FPS H.264 video that I want to downsample for online backup. I want to get to somewhere around 10% to 20% of the existing size, which will evidently require a large sacrifice in quality. I will use H.265 as the destination format.
Now I have two main knobs I can turn to achieve this: I can lower the resolution, or I can lower the quality factor for the encoder. Of course, I can also combine both approaches.
How should I approach this to preserve as much quality as possible? It's pretty clear that turning the quality way down while keeping the resolution at 720 results in some pretty terrible video, but I'm not sure that I should draw the conclusion that I should mostly use resolution decreases to achieve the size reduction.