It's also set up as my railway config file in the dashboard forgot to mention

The config you provided is for a nixpacks.toml file, not a railway.toml file, rename the railway.toml file to nixpacks.toml

Ok if I rename it do i need to change the config-as-code to nixplacks.toml or is it completely unrelated things? It's a bit confusing to me

The config as code thing is railway.toml, the config you provided in your original message should be put into a nixpacks.toml file.

Yeah but I'm asking if i need to name this file somewhere else , or if creating the file is enough? It's still not working

It's a single file, I'm not sure what you mean by "somewhere else".

A nixpacks.toml with these contents should be placed at the root of the project -

[phases.setup]
    nixPkgs = ["...", "ffmpeg"]

yeah that's exactly what i have right now and it's not working. Where in the logs will it be shown if it's installing?

nvm it's working, what I had to change for context:

My backend was deploying from a subfolder, nixpacks.toml needs to be in backend root not repo root

Glad it's working!

Where in the logs will it be shown if it's installing?

In the build table at the top of the build logs

Now I have a separate issue, it seems ffmpeg doesn't actually load in my application:

I run this:

try:
    [subprocess.run](subprocess.run)(["ffmpeg", "-version"], check=True)
except subprocess.CalledProcessError as e:
    raise HTTPException(
        status_code=500, detail="ffmpeg is not installed or not accessible" + str(e)
    )

It fails on this check, is this normal behavior or is there something wrong with my configuration?

More specifically i have this in my logs:

ffmpeg: /lib/x8664-linux-gnu/libc.so.6: version `GLIBC2.36' not found (required by /nix/store/xpxln7rqi3pq4m0xpnawhxb2gs0mn1s0-gcc-12.3.0-lib/lib/libstdc++.so.6)

Ok again I fixed it, use this instead:

[phases.setup]
nixPkgs = ["…", "ffmpeg"]