pdfpc: Fix gstreamer video playback issue #73321

[KnairdA]

Motivation for this change

Fixing issue #73321 which prevents videos from being played in PDF presentations which is one of the main features provided by pdfpc.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

Fixes: #73321

[worldofpeace]

Weird that it didn't bail out https://github.com/pdfpc/pdfpc/blob/66bbd9c1c9626ac23fe9b391775e2680b05af332/src/CMakeLists.txt#L17

[veprbl]

For some reason this didn't work for me. I do:

nixpkgs-review pr 78125 
wget https://github.com/pdfpc/pdfpc/releases/download/v4.3.0/pdfpc-video-example.zip
nix run nixpkgs.unzip -c unzip pdfpc-video-example.zip
cd pdfpc-video-example/
pdfpc -wS video-example.pdf

and it freezes the viewer. If I do it without "-wS", it just flips to the next page when I click.

[KnairdA]

Do you get any error message? When it failed for me the viewer did not freeze but simply print out that some codec was missing. To make sure, I verified that it works not only using my own files but also using the example linked in your comment. Any ideas?

[veprbl]

@KnairdA
I don't get any error, like before. If I run nix-shell with --pure flag I get "Could not acquire DBus bus." on start. If I run with fluxbox instead of mate I also get

(pdfpc:1185): dbind-WARNING **: 21:24:36.351: AT-SPI: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files

[veprbl]

@KnairdA
If you are sure that this fixes the problem for you (you confirm that it doesn't work for you without this patch), then let's merge this PR.

[KnairdA]

Yes, that is the case. With this patch both the "pdfpc-video-example" and various other videos I tested work without issue.

[worldofpeace]

@KnairdA
I don't get any error, like before. If I run nix-shell with --pure flag I get "Could not acquire DBus bus." on start. If I run with fluxbox instead of mate I also get

(pdfpc:1185): dbind-WARNING **: 21:24:36.351: AT-SPI: Error retrieving accessibility bus address: org.freedesktop.DBus.Error.ServiceUnknown: The name org.a11y.Bus was not provided by any .service files

That means services.gnome3.at-spi2-core isn't enabled.