How to convert .avc videos to .mpg4 format.
Converting MPEG-4 Advanced Video Coding Movie Format directly to MPEG-4 Video Files (.avc to .mpg4 conversion) is certainly possible and should be quite straightforward, even though your options are limited.
Your only option appears to be the Freemake Video Converter, which allows users to import AVC videos and export them in MPG4 format.