gst: Add pispconvert GStreamer element

Add a GStreamer element for hardware-accelerated image scaling and
format conversion using the PiSP Backend.

Features:
- Single and dual output support
- DMABuf input/output for zero-copy pipelines
- Software buffer fallback
- Crop support with per-output configuration
- Format conversion between RGB, YUV420, YUV422, etc.

Signed-off-by: Naushir Patuck <naush@raspberrypi.com>

Author: naushir

README.md

@@ -24,5 +24,50 @@ libpisp_dep = dependency('libpisp', fallback : ['libpisp', 'libpisp_dep'])
 
 Alternatively [pkg-config](https://www.freedesktop.org/wiki/Software/pkg-config/) can be used to locate ``libpisp.so`` installed in of the system directories for other build environments.
 
+## Command-Line Tools
+
+### convert
+
+A simple command-line image converter that uses the PiSP Backend for hardware-accelerated format conversion and scaling.
+
+```sh
+pisp_convert input.yuv output.rgb \
+    --input-format 1920:1080:1920:YUV420P \
+    --output-format 1280:720:3840:RGB888
+```
+
+Format strings use the form `width:height:stride:format`. Use `--formats` to list available formats, or `--list` to enumerate available PiSP devices.
+
+## GStreamer Element
+
+libpisp includes a GStreamer element (`pispconvert`) that provides hardware-accelerated image scaling and format conversion using the PiSP Backend.
+
+### Building with GStreamer Support
+
+GStreamer support is enabled by default if the required dependencies are found. To explicitly enable or disable:
+
+```sh
+meson setup <build_dir> -Dgstreamer=enabled   # require GStreamer support
+meson setup <build_dir> -Dgstreamer=disabled  # disable GStreamer support
+```
+
+### Using the Element
+
+After installation, the element will be available as `pispconvert`:
+
+```sh
+gst-inspect-1.0 pispconvert
+```
+
+For usage examples and supported formats, see [src/gst/usage.md](src/gst/usage.md).
+
+### Testing Without Installing
+
+To test the plugin without installing:
+
+```sh
+GST_PLUGIN_PATH=<build_dir>/src/gst gst-inspect-1.0 pispconvert
+```
+
 ## License
 Copyright © 2023, Raspberry Pi Ltd. Released under the BSD-2-Clause License.

meson_options.txt

@@ -3,3 +3,4 @@
 
 option('logging', type : 'feature', value : 'auto')
 option('examples', type : 'boolean', value : false)
+option('gstreamer', type : 'feature', value : 'auto', description : 'Build GStreamer plugin')