A gathering of 50 US, European and Asian companies agreed yesterday on technical standards for home digital video cassette recorders, which could now be on the market as early next year: under the standards agreed, tapes will come in two cassette sizes, one about two thirds the size of a VHS cassette and able to record for four and a half hours, and a smaller version about half the current size, which will record for one hour; IBM Corp and Apple Computer Inc were among the participants, because the industry is interested in the basic recorders being used for data storage.