Prepend a random number to pairs of files

I have in a folder, pairs of files, mp4 and srt subtitle files. e.g. video1.mp4 video1.srt video2.mp4 video2.srt I want to prepend a random number to each video file but I must also prepend the same number to the set file. Does anyone know how I can do this? I'm using a mac, so it could be a bash script, automator, or even PowerShell.