how could I convert 3gp to mp4 with avconv
 

ffmpeg seems to be deprecated, so I'm using avconv, to convert 3gp to mp4...
any help what is the correct syntax for this?

thanks

Firstly if you have ffmpeg, you can still use it. I don't believe it is deprecated and they are still developing it. http://www.ffmpeg.org/ Certain distributions have avconv and have it such that if you invoke ffmpeg it prints out information saying that ffmpeg is deprecated. You can get ffmpeg from the link shown above.

I know for ffmpeg it is -i for the infile which would be your 3gp file and then next you list your outfile, with or without options you desire. It should be capable of dealing with it; however depending on the conversion, there may be advisable outfile options to add for it. Typically I try the most minimal variation to see if that converts suitably for me. acconv is the same argument forms there too, -i for the infile and then follow with the outfile name.