Zaxel's 4K Replay Server can record 4K 10 bit YUV 422 60P video stream and at the same time play back 4K 10 bit YUV 60P video already recorded in the storage at the same time.  While being played back, the operator can select a clip from the recorded video by specifying the in point and out point and put in the play list.  The play list can be played back any time, while the input video is being recorded.