I have an Android phone app, which records videos to .3GP File format. The most important fact to remember about video file formats, is that the file-name extension identifies a container file, for which there may or may not be more than one video and audio CODEC supported.
Some users have reported problems, in getting 3GP Video Files to play, or to import, on Linux computers. This is probably the case, because this container format may in some cases store H.263 video and AMR audio. The problem here is in the fact that AMR audio is a proprietary CODEC, which cannot really be shipped for free for licensing reasons.
In my case I am in luck, because my app stores video compressed with the H.264 Video CODEC, and with the AAC Audio CODEC. That means that my video files will play and be imported into projects without effort.
I am sorry if this provides no relief to other users.