ERROR: Couldn't create NvFBC instance
Shadow Cast uses the NvFBC facility to provide efficient, low-latency framebuffer capture on X11. By default, NVIDIA disables this on most (if not all) of its consumer-level GPUs. However, there are two ways around this restriction...
- You can find a utility to patch your NVIDIA drivers in the keylase/nvidia-patch GitHub repo.
- You can obtain a "key" to unlock this feature at runtime. The key can be set at runtime via the
SHADOW_CAST_NVFBC_KEY=<BASE64 ENCODED KEY>environment variable. I use this method but I'm not sure how "official" it is, so no keys are provided in this repo. Feel free to message me about this.
In some games, the NVIDIA Capture library (NvFBC) appears to interact poorly with v-sync if your refresh rate matches the capture FPS. Try disabling v-sync. Another option you can try is to set the following environment variable when capturing...
$ SHADOW_CAST_STRICT_FPS=0 shadow-cast ...
Please note, however, using this option will scale the output video's frame rate to match NvFBC's closest match (e.g. 62.5 in the case of a 60fps capture).
I haven't quite worked out the definitive cause of this "lagginess", but I suspect it is because NvFBC only accepts integer millisecond values as its sampling rate, so cannot exactly match Shadow Cast's frame rate. For example, 60fps would require a fractional sampling frequency of 16.666 milliseconds, and NvFBC only allows either 16 or 17 milliseconds.