osxVideoRecorder not properly working

I work with the osxVideoRecorder and have a strange issue: it cuts the last bit of the recorded video. sometimes this is even about 1 sec. somtimes it seems like it adds that part to the beginning of the recorded file. i experience that also in the osxVideoRecorderExamples. What did i do wrong? any suggestions? i am on Sierra and tried it with the buid in facetime camera. i also tried logitech c920. it seems that it is worse with the logitec, but i am not quite sure about that. thanks, michael