Discord Plays Pokémon

This is a half-baked post I decided to publish because it was clear I wasn’t ever going to finish it. You can find the source code of this project on GitHub.

Idea

Twitch Plays Pokémon, but for Discord

Prior Art

• https://github.com/DrSkunk/discord-plays-pokemon (takes screenshots, no video)
• https://github.com/mabotkin/discord-plays-pokemon (sends video to a web interface, not Discord)

Technical goals

• Low-cost to deploy on AWS.
  • It therefore shouldn’t require many cores or a GPU
• Require as few dependencies on the host as possible.
• 100% automation, no manual action required.

Challenges

• Discord doesn’t have a way for bots to stream video (there are APIs for audio), so we must use a “selfbot” or a “userbot”. This is against Discord’s terms of service, but it’s the only way forward. There are also no documented APIs for this.
  • https://github.com/discord/discord-api-docs/issues/1995#issuecomment-678550660
  • If Discord had an official API, this would’ve been a lot easier. I didn’t want to rely on an unofficial API because it would be prone to breakage.

Initial approach - webcam

Use a headful browser (Chrome) running Pokémon with EmulatorJS. Stream the video of headless browser to Discord. Use the stream video as a webcam input and pipe the audio as a microphone input.

• Create a virtual display using xvfb and xvfb-run: https://github.com/shepherdjerred/discord-plays-pokemon/blob/b8b67522ca05e0dd37c740741d7a94569d372a69/Dockerfile#L21-L25
• Use ffmpeg and v4l2loopback to create a virtual webcam device with v4l2: https://github.com/shepherdjerred/discord-plays-pokemon/blob/b8b67522ca05e0dd37c740741d7a94569d372a69/load.sh#L16
• Stream emulator output to the virtual webcam using ffmpeg: https://github.com/shepherdjerred/discord-plays-pokemon/blob/b8b67522ca05e0dd37c740741d7a94569d372a69/src/emulator.ts#L31-L42
• Turn on camera in Discord: https://github.com/shepherdjerred/discord-plays-pokemon/blob/b8b67522ca05e0dd37c740741d7a94569d372a69/src/discord.ts#L46

This would require that the host could install kernel modules since there is a dependency on DKMS.

Result

I was able to get audio working, but not video.

Pivoting - using screen share

I really wanted to get the webcam approach working because it felt relatively elegant, but I knew I could get it done quicker if I compromised. I used a real desktop environment with xvfb and no webcam. I used Discord’s screen share functionality instead.

• https://github.com/shepherdjerred/discord-plays-pokemon/commit/f54df7233a15f16001428b6180ebbee9f15096a9
• https://github.com/shepherdjerred/discord-plays-pokemon/commit/fe5c4ed5e110a253ff214676513469a2342497bb

After about two hours of effort, this yielded a working albeit slow proof-of-concept. xvfb is not hardware accelerated, so everything is happenning in software. This is a problem when you are encoding video. The application worked, but it was unacceptable slow. Even the audio was significantly delayed. I tried downsizing the resolution from 1280x720 to 640x576, but it was still too slow.

Make it fast - hardware acceleration

Next, I needed to make the application fast.

Attempting GPU acceleration with Nvidia and Chrome

• https://github.com/shepherdjerred/discord-plays-pokemon/commit/301cf153dd49f53d942e41a78eee6f4707476588
• https://github.com/shepherdjerred/discord-plays-pokemon/commit/4c4843ece8777e27eb22de99df74de66700e6306

      "--disable-software-rasterizer",
      "--disable-frame-rate-limit",
      "--disable-gpu-driver-bug-workarounds",
      "--disable-gpu-driver-workarounds",
      "--disable-gpu-vsync",
      "--enable-accelerated-2d-canvas",
      "--enable-accelerated-video-decode",
      "--enable-accelerated-mjpeg-decode",
      "--enable-unsafe-webgpu",
      "--enable-features=Vulkan,UseSkiaRenderer,VaapiVideoEncoder,VaapiVideoDecoder,CanvasOopRasterization",
      "--disable-features=UseOzonePlatform,UseChromeOSDirectVideoDecoder",
      "--enable-gpu-compositing",
      "--enable-native-gpu-memory-buffers",
      "--enable-gpu-rasterization",
      "--enable-oop-rasterization",
      "--enable-raw-draw",
      "--enable-zero-copy",
      "--ignore-gpu-blocklist",
      "--use-gl=desktop"

Selkies: https://github.com/shepherdjerred/discord-plays-pokemon/commit/f510a9f000ea2f143a1a83ec1590d8f84f4a9db5

Chrome didn’t support Web RTC hardware acceleration on Linux, but Firefox did

• https://github.com/shepherdjerred/discord-plays-pokemon/commit/082fa39ce9dfc7fb0e1df7817fe7dc5e958cb62e

Switch to Selenium due to Puppeteer limitations:

• https://github.com/shepherdjerred/discord-plays-pokemon/commit/7696cbe9a92641e33470ddd8411fea408b189076

Polish

• Disable screensaver
• Auto-saving
• Auto-loading game
• Auto-loading most recent save
• Turning bot off during inactivity
• Web interface
• Automatically setting Discord preferences for audio/video
• Fully automating the process

Resources

• https://aixxe.net/2021/04/discord-video-bot