USM

USM is a video format commonly used by the PS3 and some other consoles. In Persona 5, USM files contain 2D anime cutscenes, pre-rendered 3D cutscenes, and various videos displayed on in-game objects like TV screens, list here: Movie (P5).

VGMToolbox
VGMToolbox is a free C# based tool designed for VGM (video game music) collectors and dumpers. However, it also contains tools for extracting and converting USM video to usable files. You can get VGMToolbox here.

To extract USM files in VGMToolbox, go to Misc. Tools > Stream Tools > Video Demultiplexer and select "USM (CRI Movie 2)" in the Format box. Then simply drag and drop your USM files you wish VGMToolbox and they will automatically begin to be extracted. The final result will be two separate file types: M2V (which contains video, but not audio), and ADX (which contains audio, but not video). In some cases, M2V files may appear pixelated, though this can be corrected with FFMpeg. In order to convert ADX to usable audio or combine the video and audio files, you will need the other tools listed below.

ChipAmp (Winamp Plugin)
ChipAmp is a free plugin bundle for the Winamp media player that can play and convert audio files from various game consoles. It is needed to convert the ADX audio files contained within USM files to usable audio. You can get the ChipAmp plugin bundle here. If you do not already have WinAmp installed, you can get that here.

With both Winamp and ChipAmp installed, open your ADX file in Winamp. Go to your Winamp preferences (Options > Preferences or Ctrl+P), scroll down to Plug-Ins > Output, select Nullsoft Disk Writer, and click Configure at the bottom. Set up your export preferences as you wish (make sure to set Output File Type to "Force WAV file"), and click Okay when finished. When finished, click Play in Winamp and your ADX file will be converted to a WAV file.

FFmpeg
FFmpeg is a free suite of libraries and programs for handling video, audio, and other multimedia files and streams. It can depixelate M2V video from USM files, and can also recombine M2V video and WAV audio into a single MKV file. You can get it here.

To recombine M2V video and WAV audio, open Command Prompt and change directory ("cd" followed by a space and the full folder path) to your FFmpeg folder. Hit Enter, then type "cd bin" and hit Enter to navigate to the "bin" folder. Type "ffmpeg -i (filename of the video file in the bin folder).m2v -i (filename of the audio file in the bin folder).wav (file name you want to call the merged video).mkv" and hit Enter. When it's finished, your merged video will be in FFmpeg's bin folder.