v4l-utils: fix cross-compilation

[avnik]

Fix cross-compilation (aarch64-multiplatform tested)

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[prusnak]

Since this is a big rebuild, this should target staging

[avnik]

@prusnak I agree, moved to staging as requested

[Yarny0]

Some tests on x86_64-linux, after cherry-picking the commit onto current nixos-unstable

• The output of v4l2-ctl --list-formats-ext -d /dev/video${NUMBER} seems alright.
• dvbv5-zap --adapter=${ADAPTER} --channel=channels.dvbv5 --pat --output=/tmp/output.ts ${CHANNEL_NAME} records some TV into the output file as expected (tested with dvb-t2 and dvb-s2).
• qv4l2 starts up and looks nice (I haven't tested any hardware access with this program).
• dtv-scan-tables builds (it uses ${v4l-utils}/bin/dvb-format-convert during the build).
• dvbv5-scan --get_frontend --nit ${dtv-scan-tables}/share/dvbv5/dvb-t/${SOME_TRANSPONDER_FILE} finds a lot of dvb-t channels, as it should.
• mpv av://v4l2:/dev/video${NUMBER} shows a webcam's video stream.
• I'm regularly using something like ffmpeg -f v4l2 -framerate 30 -video_size 1280x720 -input_format mjpeg -i /dev/video${NUMBER} -vf 'scale=4*iw:-1,crop=1280:720,format=yuv420p' -f v4l2 /dev/video${NUMBER_LOOPBACK} to zoom my webcam's picture and feed it into a v4l2-loopback device. This still works.
• mpv dvb://${CHANNEL} works (tested with dvb-s).

I can't judge the cross-compiling mechanism; superficially it looks alright to me.

Dear @avnik: Thanks for your contribution. Would you like to join me as a maintainer of this package? You seem to know a lot about its build process ... likely more than I do.

[avnik]

@Yarny0 thanks for offering, but I use it only indirectly as mpv dependency, this fix is part of my routine duty supporting cross-compilation in downstream distro (ghaf). But you always could enlist my help if have any build issues here.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-already-reviewed/2617/2495

[bjornfor]

What does qt5 -> qt6 have to do with fixing cross-compilation?

[avnik]

@bjornfor It already qt6, I just streamlined it to plain callPackages (it correct if I remember right, and allow move to by-name hierarchy in future)

-   v4l-utils = qt6.callPackage ../os-specific/linux/v4l-utils { };
+   v4l-utils = callPackage ../os-specific/linux/v4l-utils { };