Create a couple dummy video files with ffmpeg

make_dummy_videos_ffmpeg.sh

# Create video w/ red background
ffmpeg -f lavfi -i color=color=red -t 3 -vf scale=64:48 test_video_no_audio.mp4

# Make some dummy audio
ffmpeg -f lavfi -i "sine=frequency=1000:duration=3" -ac 2 dummy_audio.wav

# Add dummy audio to the previous video
ffmpeg -i test_video_no_audio.mp4 -i dummy_audio.wav -map 0:v -map 1:a -c:v copy -shortest test_video_audio.mp4