resolved the issue by adding more options to the ffmpeg subprocess:
_ffmpeg_process = subprocess.Popen(('/home/ubuntu/encoder/bin/ffmpeg','-re', '-i', '-', '-profile:v', 'baseline', '-preset', 'ultrafast','-c:v', 'libx264','-pix_fmt', 'yuv420p', '-vf', 'scale=1280:720','-crf','30', '-b:v'...