There are many softwares available in market both paid and free. As we are concern about free softwares. It’s difficult to find any free software which could do this work. So if you want to download the whole playlist of YouTube in HD mp3 format then you should use some type of grabber or auto downloader. Trial version of any software won’t give you freedom to do everything. There is always some restriction. So I recommend you to download some cracked version from torrent or direct. (Direct download might be more frustrating because of ads and other stuffs so I recommend to go for torrent.) Find suitable torrent for both setup and crack file and download it. If you can’t download torrent file because of your college proxy connection follow this link.
In my case I use YTD Pro version to download bulk videos or whole playlist. Although you can download upto 100 videos at a time. It also has inbuilt converter. So you can convert during download without wasting any time.
Link of YTD Pro is given below which works fine as I have tested it.