ffmpeg module does not rebuild according to arch

[busterbogheart]

We are using ffmpeg-static in our Electron app, but when the universal build is created, only the arm64 ffmpeg binary exists. I have confirmed that the ffmpeg-static module can be rebuilt with an arch param (npm rebuild --arch=arm64 -f ffmpeg-static, then confirmed with file node_modules/ffmpeg-static/ffmpeg) and the correct binary is created/downloaded. But when running the universal build, only os.arch() seems to be respected (which is an M1 machine in CircleCI).

If there were hooks in the universal build process, or some env vars set, I could manually rebuild this one module according to an arch. For example this ffmpeg module does read process.env.npm_config_arch, so if I were able to set that in between the x64 and arm64 builds (or electron/universal did), the module would build the correct ffmpeg binary.

[busterbogheart]

It seems like there is just one step missing in the middle here, but I can't seem to find it. Does anyone have a clue?