.. _concurrent-camera-access:

Concurrent Camera Access in CiV
###############################

This tutorial explains a camera mediation solution.

Camera mediation overview
*************************

To overcome the camera sensor hardware resource limitation of only one
application being able to use the camera at a time, we’ve developed a
camera sharing solution. With this solution, the preview data is shared
and available to the host OS and a guest OS in a secure manner.

Camera mediation support in CiV
*******************************

We provide a virtual camera service to enable multiple v4l2loopback
virtual nodes. These nodes are created during device bootup, and all
these nodes are available and capable of streaming data in MJPEG or YUV
format. These nodes can be used by multiple host applications as well as
multiple guest OSes for simultaneous camera operations.

We provide a host camera service that runs in the user space of Ubuntu
and enables an interface between the v4l2looback device nodes and the
guest via vsock.

The camera vhal on the guest is a generic virtual HAL developed to
interact with the host camera service to get camera data and provide the
camera content to the existing camera services in Android OS.

.. figure:: images/fig1-block-diagram-camera-mediation-CiV.png
   :width: 6.49167in
   :height: 3.44167in

   Figure 1: Block diagram of camera mediation in CiV

Figure 2 below is a screenshot of the host and guest camera applications
sharing the same camera resource simultaneously.

:program:`ffplay` is the host application using the virtual camera node
:file:`/dev/video6`.

AOSP on an Intel platform is the Celadon in virtual machine running on
the guest OS, using the virtual camera node :file:`/dev/video7`.

.. figure:: images/fig2-concurrent-camera-access.png
   :width: 6.49306in
   :height: 3.01389in

   Figure 2: Concurrent camera access on host and guest OS

Enabling camera mediation in CIV:
*********************************

#. Run the setup host script to install the host camera server and Intel
   virtual camera service.

   .. code-block:: bash

      sudo -E ./scripts/setup_host.sh

   After a successful execution of setup, two host virtual nodes are
   generated: :file:`/dev/video6` and :file:`/dev/video7`

#. Set the maximum supported resolution for the video0 node using the
   following command:

   .. code-block:: bash

      sudo v4l2-ctl -d /dev/video0
      --set-fmt-video=width=1920,height=1080,pixelformat=MJPG

#. To know your camera’s supported resolution and format, run the
   following command:

   .. code-block:: bash

      sudo v4l2-ctl -d /dev/video0 --list-formats-ext

#. Modify the :file:`~/.intel/.civ/instance.ini` file by adding:

   .. code-block:: bash

      camera_med=y

#. Before starting Android, make sure virtual device nodes :file:`/dev/video6`
   and :file:`/dev/video7` are present with host OS. If not, re-run this
   command:

   .. code-block:: bash

      sudo –E ./scripts/setup\_host.sh

#. Launch Android using :command:`vm-manager -b instance`. This starts the host
   camera service.

Camera USB passthrough limitation
=================================

The camera sensor is a hardware resource that can be used by only one
application at a time; in a virtualized environment, only one running OS
can use the camera.

If there are cases where image processing or IA operations need to be
done on the data before rendering the image, then the developer/consumer
must intercept preview data for such operations.

This problem exists even with a virtualization environment as the camera
can be used only on the host or in one of the guest OSes. With this
limitation, it’s hard to make the best use of virtualization.

Known Issues:
*************

a. The camera service implementation is only for a single camera.

b. Camera hot plug is not supported.