3GP is a simplified version of the MPEG-4 Part 14 (MP4) container format, designed to decrease storage and bandwidth requirements in order to accommodate mobile phones. It stores video streams as MPEG-4 Part 2 or H.263 or MPEG-4 Part 10 (AVC/H264), and audio streams as AMR-NB, AMR-WB, AMR-WB+, AAC-LC or HE-AAC.
Windows Essentials Codec Pack supports the following formats:
3GP, AAC, AC3, APE, AVI, DivX, 3ivx, DAT, h.264, x264, AVC, Nero Digital, DTS, FLV, FLAC, HD-MOV, MPEG-1, MPEG-2, M4A, MPC, MOD, MKV/MKA, MTM, OFR, TTA, OGG/OGM, S3M, Vorbis, VOB, WavPack, ATRAC3, XviD, XM, WV, UMX.
The 3ivx MPEG-4 encoder produces industry-leading compact high quality MPEG-4 Audio and Video and is distributed as a plug-in for QuickTime as well as plug-ins for Video for Windows and DirectShow.
This allows you to encode MPEG-4 Audio and Video in AVI, MOV or MP4 files with the encoding application of your choice.
FFDShow MPEG-4 Video Decoder
FFDShow MPEG-4 Video Decoder is a set of DirectShow filters and VFW codec for video compression, decompression and processing and audio compression and processing. You can play almost any movie using ffdshow.
If you're interested in codecs, you can go to these aticle: