How to install accelerated GStreamer rather than open-source GStreamer

I’m quite a newbie to accelerated GStreamer and I’m trying to figure out the correct way to install the accelerated version instead of the open-source version onto my Ubuntu 18.04.4 LTS.
What I did so far is following this installation instruction(nvidia user guide) by entering :

$ sudo apt-get update
$ sudo apt-get install gstreamer1.0-tools gstreamer1.0-alsa \
     gstreamer1.0-plugins-base gstreamer1.0-plugins-good \
     gstreamer1.0-plugins-bad gstreamer1.0-plugins-ugly \
     gstreamer1.0-libav
$ sudo apt-get install libgstreamer1.0-dev \
     libgstreamer-plugins-base1.0-dev \
     libgstreamer-plugins-good1.0-dev \
     libgstreamer-plugins-bad1.0-dev

I found that nvv4l2decoder is a accelerated-GStreamer-specific decoder, which I thought could be used to tell whether the accelerated GStreamer is installed rather than the open-source version.
So I enter the following to test:

gst-launch-1.0 videotestsrc ! qtdemux ! queue ! h264parse ! nvv4l2decoder ! nv3dsink -e

And it returns:

WARNING: erroneous pipeline: no element "nvv4l2decoder"

Based on the output, I came to the conclusion that the accelerated version is not installed. So I post a topic here the other day and was informed that I should install nvidia-l4t-gstreamer.

So now I’m trying to install the nvidia-l4t-gstreamer following the instructions here.
But when I enter

sudo apt update

it returns an error:

Get:1 https://repo.download.nvidia.com/jetson/common r32.4 InRelease [2,552 B]
Get:2 https://repo.download.nvidia.com/jetson/t194 r32.4 InRelease [2,565 B]
Err:1 https://repo.download.nvidia.com/jetson/common r32.4 InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0D296FFB880FB004
Hit:3 http://ports.ubuntu.com/ubuntu-ports bionic InRelease   
Get:4 http://ports.ubuntu.com/ubuntu-ports bionic-updates InRelease [88.7 kB]
Err:2 https://repo.download.nvidia.com/jetson/t194 r32.4 InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0D296FFB880FB004
Get:5 http://ports.ubuntu.com/ubuntu-ports bionic-backports InRelease [74.6 kB]
Get:6 http://ports.ubuntu.com/ubuntu-ports bionic-security InRelease [88.7 kB]
Reading package lists... Done                                 
W: GPG error: https://repo.download.nvidia.com/jetson/common r32.4 InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0D296FFB880FB004
E: The repository 'https://repo.download.nvidia.com/jetson/common r32.4 InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: GPG error: https://repo.download.nvidia.com/jetson/t194 r32.4 InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 0D296FFB880FB004
E: The repository 'https://repo.download.nvidia.com/jetson/t194 r32.4 InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

Seems like I need to get the public key 0D296FFB880FB004.

I have the following questions for now:

  1. Before I go on solving this issue, is this the right way to install the accelerated GStreamer? If not, how should I get the accelerated version installed?
  2. What does accelerated GStreamer exactly mean? Does accelerated GStreamer equal the plain open source version plus some hardware-accelerated plugins or they are the accelerated and open-source version two totally different things which require different installation methods?

Any help would be really appreciated. Thanks.

Operating system: Ubuntu 18.04.4 LTS
Architecture: arm64

Hi,
Could you re-install system image through SDKManager? If you use SDKManager for installation, the plugins shall be present by default and no need to execute manual steps.