enable download missed video's

I would like the ability to download the video's from specific channels that have missed downloading of video's due to errors/crashes or bugs in MHDL that causes me to miss a number of videos before a fix is introduced and i am only able to download so far back , but still miss videos. I want it to be able to search through all a channels collection of videos and somehow compare them with the ones I've downloaded and then download the one's I'm missing.