Ok, I'm completely baffled... this package is working fine for pdfs with video on Ubuntu with wrapProgram, but not NixOS. For it to work on NixOS, I can do the following:

> pympress has_video.pdf
[ video fails ]
> nix-shell -p pympress
$ pympress has_video.pdf
[ video succeeds ]

Any idea why this only works in a shell?

This pull request has been mentioned on Nix community. There might be relevant details there:

https://discourse.nixos.org/t/ld-library-path-not-set-for-application-unless-in-shell/3060/1

Do you have an example of PDF with video that we could try?

@jtojnar here's an example, note that both files need to be in same directory & must open with pdf player that supports video (eg okular or pympress in a nix-shell per #62137 (comment) ;):
https://open-science.s3-us-west-2.amazonaws.com/pdfvid/bayesian_opt.mp4
https://open-science.s3-us-west-2.amazonaws.com/pdfvid/video.pdf

Works fine for me in pympress not executed in nix-shell.

@jtojnar what platform? I just tested on two different NixOS machines with sandboxing and video fails unless in a shell. It worked fine however on Ubuntu. I don't think vlc is available unless in the shell for some reason

I just ran the following commands on NixOS unstable with sandboxing enabled:

$ git hub pull checkout 62137
Fetching pull/62137/head from git@github.com:NixOS/nixpkgs.git
$ nix-build -A pympress
/nix/store/wxhipgsg3qg0fajad28zv9rji76s7jb9-pympress-1.2.0
$ result/bin/pympress ~/Documents/video.pdf
[00007fb2f0006990] cache_read stream error: cannot pre fill buffer
[00007fb2f8001310] cache_read stream error: cannot pre fill buffer
[00007fb2f80189c0] mjpeg demux error: cannot peek
[00007fb2f00212e0] mjpeg demux error: cannot peek
[000000000192d270] main input error: Your input can't be opened
[000000000192d270] main input error: VLC is unable to open the MRL 'file:///home/jtojnar/Documents/bayesian_opt.mp4'. Check the log for details.
[00000000019234c0] main input error: Your input can't be opened
[00000000019234c0] main input error: VLC is unable to open the MRL 'file:///home/jtojnar/Documents/bayesian_opt.mp4'. Check the log for details.

I do see the player but clicking play does not seem to do anything:

@tbenst any motivation to continue with this PR?

@aanderse yes definitely. I’m a bit at a loss why video works in a nix-shell but not otherwise. Perhaps nix-shell isn’t as tight of a sandbox and can access system vlc. In that case the problem may lie with python-vlc

nix-shell is not sandboxed at all. It can run in a clean environment (like env -i) when you supply --pure flag to it but that’s all.

I can confirm that VLC is indeed loaded on NixOS without nix-shell as I do not have VLC installed but I see errors from VLC when I try to play the video.

How does the failure manifest for you? Do you see the player but it does not play? What do you have in console?

@jtojnar ah thanks for that, and for the continued help! I'm away from my NixOS box on a poor internet connection, so I'll dive back in on this in a week or so. My recollection is I see the same error you report. Additional info is available in the log file /tmp/pympress.log, which shows this error:

ERROR:pympress.media_overlay:Video support using VLC is disabled.
Traceback (most recent call last):
  File "/nix/store/56fpikjys6a693qfvsrqnhh8cc40vhxh-pympress-1.2.0/lib/python3.7/site-packages/pympress/media_overlay.py", line 548, in <module>
    VLCVideo._instance = vlc.Instance(vlc_opts)
  File "/nix/store/dsm2g8w0vmih9piz8znzbkygy8im4w96-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 1821, in __new__
    return libvlc_new(len(args), args)
  File "/nix/store/dsm2g8w0vmih9piz8znzbkygy8im4w96-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 4618, in libvlc_new
    ctypes.c_void_p, ctypes.c_int, ListPOINTER(ctypes.c_char_p))
  File "/nix/store/dsm2g8w0vmih9piz8znzbkygy8im4w96-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 280, in _Cfunction
    raise NameError('no function %r' % (name,))
NameError: no function 'libvlc_new'

Which suggests that python-vlc is not finding VLC for some reason. Perhaps this is why it works (read: video plays on click) for me in nix-shell: I have vlc installed.

I redownloaded the MP4 file and now the video plays.

Could you rebase to resolve the merge conflict and also use separate commit per package?

@jtojnar happy to once can confirm this issue is fixed. I just followed the exact same steps as you but video did not work. I'm also on NixOS unstable with sandboxing enabled.

❯ mkdir ~/Downloads/pympress

❯ cd ~/Downloads/pympress

❯ wget https://open-science.s3-us-west-2.amazonaws.com/pdfvid/bayesian_opt.mp4

❯ wget https://open-science.s3-us-west-2.amazonaws.com/pdfvid/video.pdf

❯ cd ~/code/nixpkgs

❯ git checkout origin/pympress

❯ nix-build -A pympress       
these derivations will be built:
  /nix/store/pq8b4ysjavk8sfxyv5scydqxnx9arjwg-pympress-1.2.0.drv
building '/nix/store/pq8b4ysjavk8sfxyv5scydqxnx9arjwg-pympress-1.2.0.drv'...
[...]
/nix/store/wxhipgsg3qg0fajad28zv9rji76s7jb9-pympress-1.2.0

❯ result/bin/pympress ~/Downloads/pympress/video.pdf 
^C

❯ cat /tmp/pympress.log                             
ERROR:pympress.media_overlay:Video support using VLC is disabled.
Traceback (most recent call last):
  File "/nix/store/wxhipgsg3qg0fajad28zv9rji76s7jb9-pympress-1.2.0/lib/python3.7/site-packages/pympress/media_overlay.py", line 548, in <module>
    VLCVideo._instance = vlc.Instance(vlc_opts)
  File "/nix/store/7iidq681h2rm15xs4jci02dc4f60184n-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 1821, in __new__
    return libvlc_new(len(args), args)
  File "/nix/store/7iidq681h2rm15xs4jci02dc4f60184n-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 4618, in libvlc_new
    ctypes.c_void_p, ctypes.c_int, ListPOINTER(ctypes.c_char_p))
  File "/nix/store/7iidq681h2rm15xs4jci02dc4f60184n-python3.7-python-vlc-3.0.6109/lib/python3.7/site-packages/vlc.py", line 280, in _Cfunction
    raise NameError('no function %r' % (name,))
NameError: no function 'libvlc_new'

Do you see a different error when you drop LD_LIBRARY_PATH? Or what does strace -f tell you about libraries being loaded?

@jtojnar, nope, dropping LD_LIBRARY_PATH does not change anything.

I just noticed on Ubuntu that video works when I'm in bash but not in zsh, haven't verified on NixOS yet.

edit: any tips on using strace -f? I see a crazy deluge of information

Rebased. I think the issue is per https://github.com/NixOS/nixpkgs/pull/62137/files#r289532543. Turns out find_library is basically broken (intentionally) in NixOS #27751, so source patching is only way to go. I'm trying to do this with the following line:

patchPhase = ''
    substituteInPlace "vlc.py" \ 
      --replace "p = find_library('vlc')" 'p = "'' + vlc + ''/include/lib/libvlc.so.5"'
    '';

But this gives: substituteStream(): ERROR: Invalid command line argument:. Any tips?

Edit: I also tried substituteInPlace "vlc.py" --replace "p = find_library('vlc')" "p = \"\''${vlc}/include/lib/libvlc.so.5\""

Except for the confusing quoting, I do not see any issue at a glance. I would suggest using a patch file with substituteAll, since that will make the future need for change obvious by being unable to apply the patch, and also because it is much more elegant. Either way, you should neve override patchPhase, as it will silently break patches attribute.

And I do not think #27751 has anything to do with this. It only removed ldconfig lookup, not dl lookup, which seems to work fine.

@jtojnar is there an elegant way to do a patch file with a dynamic path? Not sure how to point to ${vlc} without hardcoding the incredibly fragile "/nix/store/1yy8jfyij1f8l7hhnxl2qvavdh2vmcl2-vlc-3.0.6"

As for find_library, maybe I'm wrong but #25763 (comment) makes me think that this function is more-or-less broken on NixOS.

See

Video is now working! I think this is good to go. Thanks @jtojnar for patient help.

Made changes requested, but left postInstall wrapping as video did not work without. Also, I tried adding tests in, but got stymied by a required config file that is generated at runtime. Hopefully can leave that for future work as does appear satisfactorily functional.

Edit: oops, an example layout file made it in this commit. Is there an easy way for me to copy this to ~/.config/pympress for package test, or would that break sandbox? If so the tests may work

@jtojnar finally had a chance to debug this. Was a simple fix, patch needed to be ${vlc}/lib/libvlc.so.5 not ${vlc}/include/lib/libvlc.so.5

After final review, I think this is ready to go!

@jtojnar that's terrific, thanks so much for your patient help! I learned a lot :)