ffmpeg not creating audio file

I'm trying to write raw s16le audio to an audio file using ffmpeg. This is the command I'm using:

ffmpeg -y -f s16le -acodec pcm_s16le -ar 44100 -ac 1 -i - -vn -ar 44100 -ac 1 OUTPUT_FILE.wav

After this command is handled I use stdin to put data in the encoder like this:

fwrite(samples_, sizeof(short int*), numSamples, audioffmpeg); 

where samples_ is a short int* with a number of numSamples combined. At the moment I'm trying this per sample (so numSamples is 1).

For some reason this isn't creating a new file. Although, when I use a previously created file as input (so I don't use stdin) it does create a new file.

FFmpeg doesn't seem to be outputting so I can't give that