H.264 decodes in hardware (the session reports UsingHardwareAcceleratedVideoDecoder YES), but 4K decode is slow next to HEVC on the same GPU:
| clip (2 s, 60 fps) | decode rate |
|---|---|
| H.264 1080p | 138-140 fps |
| H.264 2160p | 29-34 fps |
| HEVC 1080p | about 820 fps |
| HEVC 2160p | 243-251 fps |
AVPlayer plays the H.264 4K clip at about 33 fps (63-71 of 120 frames in 3 s). HEVC 4K plays every frame.
Tested on RTX 5070 Laptop (GB206, 10DE:2D18), Lenovo Legion 5 15IAX10, macOS 26.7.1 (25G241), stock 2.3.7. Evidence: project-legion evidence/native/featuretest-2026-10-18/A/vid.vt.txt, vid.play.txt. Decoder: upstream libnvdec_h264.
Also seen once (pass A smoke run): the first AVPlayer playback of the H.264 1080p clip after the decoder had been idle delivered 0 frames in 3 s; the same clip played all 120 frames in every later run. Looks like a cold-start delay in the H.264 decoder session.