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Decoding Jetson H.264 Images on Non-NVIDIA Powered Systems
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.. figure:: :ir_lfs:`<resources/isaac_ros_docs/concepts/compression/h264/image_view_h264_decoded.png>`
    :width: 400px
    :align: center

Overview
------------

Using hardware-accelerated Isaac ROS compression to H.264
encode data for playback through Isaac ROS H.264 decoder on
NVIDIA-powered systems is fast and efficient. However, you may need
to decode recorded data on systems that are not NVIDIA-powered.
Fortunately, the output of the ``isaac_ros_h264_encoder`` package can
be reformatted to work with other available ROS 2 decoder
packages.

This tutorial shows you how to replay a rosbag recorded on a Jetson
using a third-party H.264 decoder `image_transport
plugin <https://github.com/clydemcqueen/h264_image_transport>`__
used in `FogROS2 <https://github.com/berkeleyAutomation/FogROS2>`__.

The launch file replays a target rosbag recorded with
``isaac_ros_h264_encoder``. It is recorded through a node that reformats the compressed
messages for compatibility. Then the third-party
decoder is used to display it in an image view window.

Tutorial Walkthrough
--------------------

1. Complete the quickstart :ref:`here <repositories_and_packages/isaac_ros_compression/isaac_ros_h264_decoder/index:quickstart>`.
2. Clone the following third-party repository into your workspace:

   .. code:: bash

      cd ${ISAAC_ROS_WS}/src
      git clone https://github.com/clydemcqueen/h264_image_transport.git

      # Install dependencies for the third-party package
      sudo apt install libavdevice-dev libavformat-dev libavcodec-dev libavutil-dev libswscale-dev

3. Launch the Docker container using the ``run_dev.sh`` script:

   .. code:: bash

      cd ${ISAAC_ROS_WS}/src/isaac_ros_common && \
        ./scripts/run_dev.sh

4. Inside the container, build the third-party ``h264_image_transport``
   package:

   .. code:: bash

      cd /workspaces/isaac_ros-dev && \
        colcon build --symlink-install --packages-up-to \
          h264_image_transport isaac_ros_to_h264_msgs_packet && \
        source install/setup.bash

5. Launch the graph to bring up an image viewer that shows the decoded
   output.

   .. code:: bash

      ros2 launch isaac_ros_to_h264_msgs_packet h264_compatible_decoder.launch.py rosbag_path:=/workspaces/isaac_ros-dev/src/isaac_ros_compression/resources/rosbags/h264_compressed_sample.bag

   .. note::

      You may have to click on the “/image” to trigger window
      resizing.