No video output is produced after running demo

I am executing the following command

python tools/run_net.py --cfg demo/AVA/SLOWFAST_32x2_R101_50_50.yaml DEMO.ENABLE True DEMO.INPUT_VIDEO input.mp4 DEMO.OUTPUT_FILE output.mp4

I have also set CHECKPOINT_FILE_PATH and LABEL_FILE_PATH in the YAML config file.

I don't see any output file produced after the run

Python version = 3.7
pytorch==1.7.1
torchvision==0.8.2
torchaudio==0.7.2
cudatoolkit=10.1