Merging

Download and extract FFmpeg

Open a new command prompt as administrator and change directories to the ffmpeg bin folder.

Place your decrpyted video and decrypted audio files in this bin folder as well

In command prompt issue the command to merge the two streams ffmpeg.exe -i INPUTVIDEO -i INPUTAUDIO -vcodec copy -acodec copy FINAL

INPUTVIDEO is your video file, INPUTAUDIO is your audio file and FINAL is your merged Audio/Video file.

Congrats, you now have a playable decrypted widevine audio/video file!