possible gstreamer scenario validation

[tasos]

Hello.
I would like to ask an easy question(i think).
My scenario is the following.
I receive a stream(x264) which i edit via opencv.
I can send those edited images to ffmpeg and create a video which i
can also stream.The problem is that i can't have audio.
And the possible solutions...
Writing a program using ffmpeg's api is not something i could do right 
now,and i think
that i will face more problems during development.
I think that gstreamer could help me.
Of course i have read than sync is very important and not very easy.
I was reading about appsink here
> https://stackoverflow.com/questions/46219454/how-to-open-a-gstreamer-pipeline-from-opencv-with-videowriter
So appsink can get my edited images like they were added to the pipeline 
and then do whatever i want.
Possibly adding the audio that i want?
So my question is if something like this is possible,by only adding some 
audio stuff at the pipeline?
Could you point me to some direction or at least let me know if this is 
impossible via gstreamer.
Thank you very much!