Loss of quality while adding subtitle via FFmpeg After solving on problem I cam coming to a next one. After adding subtitles, discussed here, with the command:

ffmpeg -i grdedFinal.mov -vf subtitles=portSbs.srt gradedFinalwithSubs.mov


the quality of the generated file significantly decreased. The original file was of size 1,5GB whereas the resulting file was of size ~300MB. The subtitles are added correctly but the compression is unnecessary. In a word I would like for the FFmpeg to add subtitless and do only that leaving the sound and picture quality untouched.
As you are hardcoding subtitles, the video (with the subtitles added) will be re-encoded. 

You can use the CRF rate control method to modulate the quality of the output.

So, start with

ffmpeg -i grdedFinal.mov -vf subtitles=portSbs.srt -crf 18 -c:a copy gradedFinalwithSubs.mov


If the quality's not acceptable, lower that value till it is - in exchange for a larger file. Of course, don't decide based on file size but on visual quality. x264 is very good at compressing video while maintaining subjectively perceived quality.