Circa 1925, someone invents a cheap, compact film projector suitable for home use. It becomes a popular fad among the rich, but remains inaccessible to the masses because of the expense of film prints. Nonetheless, it popularizes the idea of watching films at home, creating a demand for a cheaper, more portable means of distributing movies for home use.
The answer is magnetic tape, a technology which had recently been invented in Germany. In OTL magnetic tape remained a cumbersome reel-to-reel affair until the 70's. But in TTL, economic demand leads to a massive investment in this technology. As a result, the compact cassette is invented several decades earlier, circa 1935. The technology completely supplants vinyl records, and is snapped up by film studios, which begin producing home versions of their films. Initially these are a niche item, but sales increase after the end of WWII, when home cinemas become a canonical fixture of every proud middle-class home.
Because this medium develops as a direct offshoot of the film industry, it is cinematic in its conventions. It consists of newsreels, short subjects, and feature-length films. There are serials, but not TV shows as we know them. There are no commercials, because cassettes are bought at shops, like records. In short, there is no distinct medium called "television". It is simply cinema in the home.
Crucially, the latency inherent in the technology allows radio to retain its relevance and prestige for much longer. People still depend on radio for up-to-the-minute news, sports, etc. Even after it becomes technologically feasible to broadcast live images, the convention persists due to habit and protective regulation fostered by the two industries. The same cultural duality that once existed between radio and cinema continues to exist to the present day, except that cinema migrates from theaters into people's houses.