age old problem of filling up your ram with jit.matrixset when all you want is a 20 minutes video delay. while helping out on a patch i found jit.qt.record 'frame' attribute which was unknown to me. seems you can read a jit.qt.record stream while its recording. enter endless delays .

frame (1 int) Frame number (default = -1 disabled) > Typically, the jit.qt.record object passes input matrices directly to the outlet without any processing. Setting frame to a number greater than or equal to zero (0) during recording permits viewing of the compressed, previously recorded frame specified by the frame attribute's value, while the object continues to record new frames.