Colorize Old Black-and-White Video

Because the network has no idea what a video is: it colors one still image at a time, and a minute at 30 frames a second is 1800 separate jobs. That also explains the flaw you have to watch for — the model decides a coat is brown in one frame and gray two frames later, and the eye reads that flicker instantly even though each individual frame looks fine. Short clips of a stable scene come out far better than long ones with cuts and camera moves. The model itself is a download of about a hundred megabytes that happens once and is then kept, and the work runs on your own machine, so a laptop with hardware acceleration will be several times faster than one without.

Every frame goes through the network, so the cost is duration times resolution and nothing else — a thirty-second home movie at 480p is comfortable, a ten-minute feature clip at 1080p is not. The model itself downloads once, about 108 MB, and is cached afterwards, so the wait you notice on a second clip is the painting, not the loading. Trim to the passage worth coloring before you start.

Yes — the audio track is copied unchanged into the MP4 and WebM outputs. GIF and the PNG-frame ZIP have no audio container, so audio is dropped automatically for those formats.

That is the usual first result, and there are two dials for it. The skin-tone slider nudges faces and hands warmer or cooler until they stop looking like a waxwork — a small move is normally enough. If the whole picture is off rather than just the people, drop in a color photo from the same era as a reference and the palette is biased towards it; anything from 64×64 pixels up works.