It's a common, frustrating experience: you compress a video to make the file smaller, and it comes out looking noticeably worse in ways that are hard to pin down, softer, blockier, oddly colored in motion. The reason it's hard to diagnose is that a typical compression pass changes multiple things simultaneously, and each one produces a distinct kind of visual damage.
Bitrate artifacts look different from resolution loss
Low-bitrate compression shows up as blocky, mosquito-like artifacts around edges and smearing in fast motion, because the codec doesn't have enough data budget to accurately represent complex or rapidly-changing detail, so it approximates with flat blocks of color instead. Low-resolution scaling, by contrast, produces a softer, blurrier look overall, but without the blocky artifacting, since it's simply working with fewer total pixels rather than approximating within the same pixel count. If your compressed video looks blocky specifically during motion but sharp on still frames, that's a bitrate problem; if it looks uniformly soft everywhere, that's more likely a resolution problem. The Video Bitrate & Resolution Changer separates these two settings so you can test them independently.
Codec choice changes the trade-off, not just the numbers
Two videos compressed to the exact same file size can look meaningfully different if they use different codecs, since newer codecs like H.265 pack the same visual quality into less data than H.264, meaning an older codec forced to hit a small file size has to cut more corners than a modern one would at the same target. This is also why a video re-exported from an already-compressed source often looks worse than expected: each compression pass discards some detail permanently, and a second pass compresses what's left, compounding the loss rather than starting fresh. Converting between formats and comparing results is straightforward with the Video Format Converter, which is worth doing before assuming a specific bitrate setting is the culprit.