Bitrate is the size of one second.
Multiply it by the length and you have the file size. That is why every "make this video under 25 MB" tool really picks a bitrate, and why the same bitrate can look clean on one clip and blocky on another.
Your browser's own encoder compresses a generated clip twice at the same target: once at a constant bitrate, once variable. The clip has an easy part, a moving part, a very hard part and an easy part again. Every bar below is the real bytes the encoder wrote for that quarter-second.
A size limit fixes the bitrate. Spread that bitrate over more pixels and each pixel gets fewer bits. The table works out what is left for the picture at each resolution.
Bits per pixel = picture bitrate ÷ (width × height × frames per second). Bands used: 0.1 and up clean, 0.05 to 0.1 acceptable, 0.03 to 0.05 soft, below 0.03 blocky. They are a rough guide for H.264 on ordinary footage; HEVC and AV1 usually look as good with fewer bits, and grain or confetti needs more. The Video Compressor measures the real result.
Bitrates are counted in bits and in thousands. File sizes and download speeds in apps are often in bytes, sometimes in 1024s. Type one speed and see it in every unit.
For 1080p: 8-12Mbps. For 4K: 35-68Mbps. For YouTube uploads: follow YouTube's recommended bitrates.
For music: 256-320kbps MP3 or 256kbps AAC. For podcasts/speech: 128kbps. For archiving: use lossless FLAC.
Up to a point, yes. Above a certain threshold, further increases in bitrate provide diminishing returns that are imperceptible.
Spotify streams at 24kbps (low), 96kbps (normal), 160kbps (high), and 320kbps (very high, Premium only).
Right-click the video file > Properties > Details tab on Windows. Or use VLC: Tools > Media Information > Statistics.