running 'gst-inspect-1.0 avdec_h264' fails to find the plugin

[Benjamin Schleimer]

In general, running:
> gst-inspect-1.0 /usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstlibav.so

fails with this message:
(gst-inspect-1.0:20626): GStreamer-WARNING **: Failed to load plugin '/usr/lib/x86_64-linux-gnu/gstreamer-1.0/libgstlibav.so': libpgm-5.1.so.0: cannot open shared object file: No such file or directory
Could not load plugin file: Opening module failed: libpgm-5.1.so.0: cannot open shared object file: No such file or directory

Trying to install libpgm-5.1-0 failed:
> sudo apt-get install libpgm-5.1-0
[sudo] password for benjamin:
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libpgm-5.1-0 is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'libpgm-5.1-0' has no installation candidate

So I did the ugly thing:
sudo ln -s /usr/lib/x86_64-linux-gnu/libpgm-5.2.so.0 /usr/lib/x86_64-linux-gnu/libpgm-5.1.so.0
rm ~/.cache/gstreamer-1.0/registry.x86_64.bin

and now 'gst-inspect-1.0 avdec_h264' works

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gstreamer1.0-libav 1.8.0-1
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
CurrentDesktop: KDE
Date: Thu Apr 28 19:39:48 2016
InstallationDate: Installed on 2015-01-08 (476 days ago)
InstallationMedia: Ubuntu-Server 14.04.1 LTS "Trusty Tahr" - Release amd64+mac (20140722.3)
SourcePackage: gst-libav1.0
UpgradeStatus: Upgraded to xenial on 2016-04-26 (2 days ago)