The Sony Betamax home video recorder had better picture quality and some other technically superior features compared to the competing VideoHomeSystem (VHS) from JVC. However, VHS from the start had a two hour tape capacity while Beta only had one, making it more convenient to watch a movie; and JVC enthusiastically courted additional manufacturers while Beta failed to successfully popularize their format.  

ChrisBaugh recommends BreakthroughsBook for a good description.

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As I understand it, another huge factor was that Sony refused to license the Beta format to the porn industry and this helped kill the format as per PornDrivesNewTech.