Some mp4 files converted with ffmpeg are off by .01 frames/second, how can I fix this (without resampling)

Question

I have several mp4 files with a frame rate of 119.88 frames/second, I need to convert these to 29.97 frames/second without resampling.

To do this, I ran

ffmpeg -itsscale 4 -i input.mp4 -c copy output_con.mp4

However, some of these files return with a frame rate of 29.98 frames/second, this is messing me up in later analyses by throwing off some cross correlations between the mp4 files and related wav files. Any insight into how to remedy this would be much appreciated!