(1 through 5.2) define max resolution, bitrate, and buffer size. Level 3.1 = 720p30. Level 4.1 = 1080p30/1080i60. Level 5.1 = 4K. The Silicon Lottery: Why Hardware Decoding Won MPEG-2 had hardware decoders, but they were expensive. H.264's complexity (up to 400+ operations per pixel vs 60 for MPEG-2) threatened to kill software decoding on 2003-era CPUs.
When future archaeologists decode the first two decades of online video, they'll find H.264's start codes ( 0x00 0x00 0x01 ) embedded in more files than any other binary signature. That's the mark of a true standard.
| Profile | Key features | Typical use | |---------|--------------|--------------| | | No B-slices, no CABAC | Video conferencing, low-delay | | Main | I/P/B slices, CABAC, deblocking | Broadcast, SDTV | | High | 8x8 DCT, perceptual quantization, custom quant matrices | Blu-ray, HD streaming | | High 10 | 10-bit depth | Professional post-production | | High 4:2:2 / 4:4:4 | Chroma subsampling preservation | Archival, medical imaging |