lcevcencoder: Add README.md

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7330>

subprojects/gst-plugins-bad/ext/lcevcencoder/README.md

@@ -0,0 +1,62 @@
+LCEVC Encoder Build Instructions
+--------------------------------
+
+1. Download and manually install the pre-built V-Nova's LCEVC Encoder SDK:
+
+- You can get a trial pre-built V-Nova's LCEVC Encoder SDK directly just by signing up at: https://download.v-nova.com
+- There should be at least a pre-built `encoder_sdk.tar.gz` package for Ubuntu 20, Ubuntu 22 and Windows.
+- Once you have downloaded the correct package for your system, extract the tar file:
+
+```
+$ cd Downloads
+$ tar xvf encoder_sdk.tar.gz
+```
+
+- Now you need to manually install the headers, libraries and plugins in $INSTALL_DIR
+- For example, $INSTALL_DIR for Linux can be `/usr/local`:
+
+```
+$ cp -v include/*.h /usr/local/include
+$ cp -v *.so /usr/local/lib
+```
+
+- Afterwards, you need to manually create the `lcevc_eil.pc` package config file with this contents:
+
+```
+prefix=/usr/local
+includedir=${prefix}/include
+libdir=${prefix}/lib
+
+Name: lcevc_eil
+Description: LCEVC Encoder EIL library
+Version: 3.11.3
+Libs: -L${libdir} -llcevc_eil
+Cflags: -I${includedir}
+```
+
+- And finally install it under `/usr/local/lib/pkgconfig`
+
+```
+$ cp -v lcevc_eil.pc /usr/local/lib/pkgconfig
+```
+
+2. Build LCEVC encoder (lcevcencoder) plugin for GStreamer:
+
+- You can now build the lcevcencoder plugin by using the '-Dgst-plugins-bad:lcevcencoder=enabled' meson flag
+- $BUILD_DIR and $INSTALL_DIR are local build and install directories
+- For example:
+
+```
+$ cd GStreaner
+$ meson setup $BUILD_DIR --pkg-config-path=$INSTALL_DIR/lib/pkgconfig -Dgst-plugins-bad:lcevcencoder=enabled
+$ ninja -C $BUILD_DIR
+```
+
+3. Run GStreamer LCEVC encoder pipeline:
+
+- If the build was successful, you can test LCEVC encoding (H264) with the following pipeline:
+
+```
+$ gst-launch-1.0 videotestsrc pattern=ball num-buffers=1024 ! video/x-raw,width=1920,height=1080,format=I420,framerate=25/1 ! lcevch264enc plugin-name="x264" plugin-props="preset=superfast;tune=zerolatency" ! h264parse ! mp4mux ! filesink location=lcevc-sample.mp4
+```
+