OBS cannot start streaming with FFmpeg VAAPI on AMD

[MurdoMaclachlan]

With OBS version 29.0.2 I'm unable to start streaming using the FFmpeg VAAPI H.264 encoder (the only encoder it shows other than x264). I get the following error:

vainfo output below, OBS log attached. I've seen a number of similar issues to this around the internet but they've all either been on the flatpak version, which I'm not using, or are unsolved.

Trying display: wayland
Trying display: x11
vainfo: VA-API version: 1.18 (libva 2.18.2)
vainfo: Driver version: Mesa Gallium driver 23.0.3 for AMD Radeon RX 6600 (navi23, LLVM 16.0.2, DRM 3.49, 6.1.28)
vainfo: Supported profile and entrypoints
      VAProfileMPEG2Simple            :    VAEntrypointVLD
      VAProfileMPEG2Main              :    VAEntrypointVLD
      VAProfileVC1Simple              :    VAEntrypointVLD
      VAProfileVC1Main                :    VAEntrypointVLD
      VAProfileVC1Advanced            :    VAEntrypointVLD
      VAProfileH264ConstrainedBaseline:    VAEntrypointVLD
      VAProfileH264ConstrainedBaseline:    VAEntrypointEncSlice
      VAProfileH264Main               :    VAEntrypointVLD
      VAProfileH264Main               :    VAEntrypointEncSlice
      VAProfileH264High               :    VAEntrypointVLD
      VAProfileH264High               :    VAEntrypointEncSlice
      VAProfileHEVCMain               :    VAEntrypointVLD
      VAProfileHEVCMain               :    VAEntrypointEncSlice
      VAProfileHEVCMain10             :    VAEntrypointVLD
      VAProfileHEVCMain10             :    VAEntrypointEncSlice
      VAProfileJPEGBaseline           :    VAEntrypointVLD
      VAProfileVP9Profile0            :    VAEntrypointVLD
      VAProfileVP9Profile2            :    VAEntrypointVLD
      VAProfileAV1Profile0            :    VAEntrypointVLD
      VAProfileNone                   :    VAEntrypointVideoProc