Simple Gstreamer Video Element

Introduction

Simple Gstreamer Element from scratch.

Filters and filter-like elements have both input and outputs pads. They operate on data that they receive on their input (sink) pads, and will provide data on their output (source) pads. Examples of such elements are a volume element (filter), a video scaler (convertor), an Ogg demuxer or a Vorbis decoder.

Filter-like elements can have any number of source or sink pads. A video demuxer, for example, would have one sink pad and several (1-N) source pads, one for each elementary stream contained in the container format. Decoders, on the other hand, will only have one source and sink pads.

Project Structure:

.
├── AUTHORS
├── ChangeLog
├── COPYING
├── meson.build
├── NEWS
├── plugins
│   ├── gstsimplefilter.cpp
│   ├── gstsimplefilter.hpp
│   └── meson.build
├── README.md
└── tools
    ├── gstsimplefilter.cpp
    └── meson.build

2 directories, 11 files

References:

• GStreamer elements
• GStreamer Writer's Guide
• GstVideoFilter
• GStreamer filter elements

Setup GStreamer Build Env

First install dependencies:

sudo apt install build-essential python3 git ninja-build python3-pip

Install meson from the pip repo:

pip3 install --user meson

Clone and build GStreamer repos:

git clone https://gitlab.freedesktop.org/gstreamer/gst-build
cd gst-build
meson build --buildtype=debug
ninja -C build

Use build devenv environment. This command will create an environment where all tools and plugins built previously are available in the environment as a superset of the system environment with the right environment variables set.

ninja -C build devenv

Your bash become:

[gst-discontinued-for-monorepo] $

Build Gstreamer Video Element

First get the sources and cd inside:

$ git clone https://github.com/Scott31393/gst-simplefilter.git
$ cd gst-simplefilter

Than build the project. Remember that plugins can be installed locally by using "$HOME" as prefix:

$ meson --prefix="$HOME" build/
$ ninja -C build/ install

However be advised that the automatic scan of plugins in the user home directory won't work under gst-build devenv.

Instead of add the plugin into your home you can add the plugin path to the GST_PLUGIN_PATH.

export GST_PLUGIN_PATH=$GST_PLUGIN_PATH:/path-to/gst-simplefilter/build/plugins/

References:

• Getting started with GStreamer's gst-build

Use Gstreamer Video Element

To test and use gst simplefilter element just run the following gst-launch pipeline:

$ gst-launch-1.0 v4l2src ! videoconvert ! simplefilter ! videoconvert ! xvimagesink

Debug the element using:

$ GST_DEBUG=simplefilter:5 gst-launch-1.0 v4l2src ! videoconvert ! simplefilter ! videoconvert ! xvimagesink

Create New Element from Scratch

Clone gst-plugins-bad repository:

$ git clone https://github.com/GStreamer/gst-plugins-bad.git

Create GStreamer Project from Template

Go inside tools dir and create project from template using gst-project-maker:

$ cd gst-plugins-bad/tools
$ ./gst-project-maker "simplefilter"

This will create:

gst-simplefilter/
├── AUTHORS
├── ChangeLog
├── COPYING
├── meson.build
├── NEWS
├── plugins
│   ├── gstsimplefilter.c
│   ├── gstsimplefilter.h
│   ├── gstsimplefilterplugin.c
│   └── meson.build
├── README
└── tools
    ├── gstsimplefilter.c
    └── meson.build

2 directories, 12 files

Create GStreamer Element from Template

Go inside tools dir and create project from template using gst-element-maker:

$ ./gst-element-maker "simplefilter" videofilter

This will create:

gstsimplefilter.c
gstsimplefilter.h
gstsimplefilter.o
gstsimplefilter.so

Move Create Element into the Create Project

Move create element file into created plugin project directory:

$ mv gstsimplefilter.c gst-simplefilter/plugins/
$ mv gstsimplefilter.h gst-simplefilter/plugins/

Cross Compile for arm64

source /opt/fslc-xwayland/4.1-snapshot-20240610/environment-setup-cortexa53-crypto-fslc-linux
meson build
ninja -C build
sudo cp build/plugins/libgstsimplefilter.so /targetfs/usr/lib/gstreamer-1.0/
gst-inspect-1.0 simplefilter

Fix Meson Build Files

Since it is an element created by inheriting videofilter, it is necessary to add a dependency to meson.build. Other thing is that function gst_element_register is duplicated, so delete simplefilterplugin.c file and update plugin meson.build file:

References:

• fix plugin meson.build
• move from c to cpp