dd stops copying mid-way through a CD

I got a couple of old disks I'm trying to copy over to a HDD. Some of the disks worked fine and I was able to copy them using just mount and rsync, however as is it with old disks, some of the disks were failing to mount. I tired using dd to make an image of them and then ran photorec to get the files out. This worked upto some extent. My files were recovered, however I noticed that dd was only copying about half (1.5Gb out of 4.7Gb) disks for some of the drives. This was causing photorec to only recover about half of the video on the disk (Is there some better way to recover these files from the disk?) I was wondering if some unreadable section was encountered and dd just stopped copying, if so, is it possible to instruct dd to make a copy of the whole 4.7gb disk? Command I ran: dd if=input of=output