For users who need bulk conversions, JDownloader 2 is a powerful, open-source tool that is constantly updated (UPD weekly). While it doesn't convert to 3GP natively, it downloads the video, and you can pair it with a converter (see Method 3).
(3rd Generation Partnership Project file format) is a multimedia container format developed specifically for 3G mobile phones. Created by the 3GPP organization in the early 2000s, this format was designed to transmit, store, and view multimedia content over slower, lower-bandwidth mobile networks. The format uses H.263 and MPEG-4 codecs for video compression, along with AAC-LC and AMR-NB codecs for audio. 3gp king youtube upd