add readme

readme.md

@@ -0,0 +1,43 @@
+# AJA Video Cards ❤️  Nix
+
+This repo contains a Nix flake containing the open source AJA driver, utilities and
+gstreamer plugin. This allows you to use Aja video IO cards on NixOS.
+
+
+## Usage
+
+- Add the flake to your system flake's inputs.
+- Apply the overlay to your system's nixpkgs, e.g.
+  ```nix
+  nixpkgs.overlays = [ ajantv2.overlays.default ];
+  ```
+- Add the kernel driver:
+  ```nix
+  # Include the kernel module 
+  boot.extraModulePackages = [pkgs.ajantv-driver];
+  # And load it automatically
+  boot.kernelModules = [ "ajantv2" ];
+  ```
+- Include the utils/demos and gstreamer plugin:
+  ```nix
+  environment.systemPackages = [pkgs.ajantv-utils pkgs.aja-ntv2-gst]
+  ```
+
+## Gstreamer
+Summon a quick network stream: `gst-launch-1.0 ajavideosrc input-channel=0 mode=29 ! videoconvert ! jpegenc quality=20 ! multipartmux  boundary="--videoboundary" ! tcpserversink host=0.0.0.0 port=6969`
+
+NB: You must select the video mode to match what's on the input. Otherwise you will see
+something like:
+```
+Setting pipeline to PAUSED ...
+Pipeline is live and does not need PREROLL ...
+Pipeline is PREROLLED ...
+Setting pipeline to PLAYING ...
+New clock: GstSystemClock
+WARNING: from element /GstPipeline:pipeline0/GstAjaVideoSrc:ajavideosrc0: Signal lost
+Additional debug info:
+gstajavideosrc.cpp(1324): gst_aja_video_src_create (): /GstPipeline:pipeline0/GstAjaVideoSrc:ajavideosrc0:
+No input source was detected - video frames invalid
+```
+
+You can find all the supported video modes with: `gst-inspect-1.0 ajavideosrc`.