Start with the destination
A 4K label describes frame dimensions, not the codec, bit depth, frame rate, chroma sampling, or dynamic range. Two 4K files can place very different demands on an editor or playback device. Inspect the source properties and the destination limits before opening a 4K video converter or selecting a preset.
Choose whether to preserve, transcode, proxy, or downscale
Keep the original file when the editor or player handles it reliably. Transcode to an editing codec when long-GOP decoding slows the timeline; create a proxy when the computer needs lighter temporary media; and downscale to 1080p or 720p only when storage, bandwidth, or display limits justify reducing resolution. A proxy is a working copy, not a replacement for the camera original.
Changing the codec, resolution, frame rate, or HDR transfer function creates a new encoded file. It should not be described as lossless unless the selected workflow preserves the original streams. For archive work, keep the source and record the settings used for every compatibility copy.
Test color, motion, and audio
Convert one representative clip and check resolution, frame rate, color range, HDR handling, picture detail, motion cadence, audio channels, subtitles, and sync in the intended application. Check a bright scene and a fast-moving scene, then confirm the output plays from start to finish before processing the complete batch.