Video Encoding Lab

Every frame carries an entropy 'demand' — how many bits it truly needs to look clean, driven by resolution, frame rate, motion, and chroma detail. Your chosen bitrate is a fixed 'budget': spread evenly across the whole clip in CBR mode, or aimed at a target quality per scene in CRF mode. When a fast, detailed scene's demand spikes above that budget, the encoder has no choice but to round more aggressively to stay within its bit allowance — which is exactly why blocking and smearing show up first on the busiest scenes, not the calm ones.

Newer codecs squeeze the same picture into fewer bits: at matched quality, AV1 lands around half the file size of H.264, and H.265 saves roughly a quarter, thanks to smarter prediction tools. The catch this lab hints at is that those savings cost compute — AV1 can take many times longer to encode than H.264. Rule of thumb: pick the newest codec your devices can play and your time budget can afford.

Intuitively, twice the frames should need twice the bitrate — but they don't. The closer two frames sit in time, the more alike they are, so the encoder's motion compensation only stores the tiny differences between them. Going from 30 to 60 fps at matched quality usually adds only about 30–50% more bits, not 100%. The extra frames are cheap because they're nearly copies of their neighbors.