Encoding Issues to MP4 with AAC audio

When encoding video in MP4 with AAC audio, the file length is increased by 2-4 frames. I tried different programs - FFWorks, iFFmpeg, HandBrake, Adobe Media Encoder, directly from AfterEffects with AfterCodec - same result, file is 4 frames longer. Tried a different frame rate(25, 30, 50). Moreover, if you encode a file without sound, or with another audio codec - the length does not change! The only program that converts without error is MPEGstreamclip, but it is 32-bit and does not start on Catalina! Tested on Mojave and Catalina on iMac(14.2) and MacBook (Late 2012) Has anyone encountered such a problem? Thanks for the answer!