For convenience, Video Codecs can be divided into two groups.
Edit-friendly and edit-unfriendly codecs.

Edit-friendly Codecs are:
ProRes, DNxHD, DNxHR, braw, R3D, ARRIRAW

Edit-unfriendly Codecs are:
H.264, H.265, HEVC, AVC, MPEG-4

H.264 / H.265 often belongs to the “Group of Pictures (GOP)” type. “Long GOP” codecs were developed to keep the video file size as small as possible. Good for DVD, Media Players and streaming. They were never intended for further processing / editing. If you try to edit those videos, DaVinci Resolve Studio has to decode those highly compressed files. Real-time playback is rarely possible and slow, jerky playback occurs.

Blackmagic DaVinci Resolve’s “Supported Formats and Codecs” PDF is a comprehensive guide that outlines all the video and audio file formats and codecs that the software can work with. – Last update: March 2023

DaVinci Resolve Studio is capable of hardware decoding of H.264 and H.256 media, but does not support all types of H.264 and H.265 media. In addition to the codec itself, the bit depth (8-bit, 10-bit) and chroma subsampling (4:2:0, 4:2:2, 4:4:4), as well as your computer’s GPU, are also taken into account, affects whether you can take advantage of hardware decoding or not. Here is an overview of H.264 decoding support in DaVinci Resolve Studio 17.4:

For H.265, 8-bit 4:2:0 and 10-bit 4:2:0 seem to work well. But for 4:2:2 / 4:4:4 you have to be lucky to have the right GPU/CPU for DaVinci Resolve Studio to take advantage of hardware decoding.

My preferred solution is to transcode H.264/H.265 files to an “edit-friendly” codec like DNxHR. There are many tools that can transcode your footage. Here is a step-by-step guide using “Shutter Encoder“. It is a free tool that can be used to convert video footage.

Step 1 = Browse and choose your H.264/H.265 file.
Step 2 = Choose function and select DNxHR.
Step 3 = Choose HQX for 12-bit 4:2:2 Broadcast-quality.
Step 4 = Start function.

DNxHR is a data format developed by Avid for lossy compressed video data. DNxHR was originally used for video editing in post-production as an “intermediate format”. DNxHR is now used throughout the production chain. Compared to DNxHD, DNxHR enables resolutions in 4k and higher. The list below shows the different quality settings at which your acquired media can be transcoded:

DNxHR LB – 8-bit 4:2:2 – Low Bandwidth
DNxHR SQ – 8-bit 4:2:2 – Standard Quality
DNxHR HQ – 8-bit 4:2:2 – High Quality
DNxHR HQX – 12-bit 4:2:2 – 4K Broadcast-quality delivery
DNxHR 444 – 12-bit 4:4:4 – Cinema-quality delivery

AVC / H.264 / HEVC and DaVinci Resolve | Why You Need to Transcode
by Richard Lackey / richardlackey.com

What H.264/H.265 Hardware Decoding is Supported in DaVinci Resolve Studio?
by Matt Bach / pugetsystems.com

Why you should use Avid DNxHD and Apple ProRes
by David Shapton / redsharknews.com