fix: unblock ffmpeg on some broken videos

[blizzz]

Summary

On some (semi-)broken videos it might be, that we do not get information with SDTOUT and keep waiting for it. Because it is an external process, the PHP time limit is not in effect. Checking STDERR first solves this problem interestingly.

TODO

• Provide a test data video of 560x320 size to not cause flaky tests due to randome test values in \Test\Preview\Provider::dimensionsDataProvider.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[kesselb]

Thanks for taking care @blizzz 👍

I recall some older PRs that aimed to achieve the same goal. They might be useful for you:

• fix(preview): ffmpeg gets stuck when getting video cover #45722 @ncheng89
• movie preview bug fix, in some case stream reading functions may block indefinitely #43226 @jpsn123

[nickvergessen]

Updated the video, fixed cs and reuse, should be good for a final rebase

[blizzz]

Thanks for taking care @blizzz 👍

I recall some older PRs that aimed to achieve the same goal. They might be useful for you:

* [fix(preview): ffmpeg gets stuck when getting video cover #45722](https://github.com/nextcloud/server/pull/45722) @ncheng89

* [movie preview bug fix, in some case stream reading functions may block indefinitely #43226](https://github.com/nextcloud/server/pull/43226) @jpsn123

Thanks for linking them!

The latter looks interesting (this part is also in the first one), would need more testing though. If this works properly, it appears more reliable than just preferring STDERR.

[blizzz]

/backport to stable31

[blizzz]

/backport to stable30

[AndyScherzinger]

@blizzz ready to go or you want to include something from #43226 ?

[blizzz]

@blizzz ready to go or you want to include something from #43226 ?

Let's go with this and rebase the second one. Should be mergable as is if the relevant tests remain green.

[kesselb]

Tested and works 👍

I don't understand why, but it's nice 😆

[kesselb]

/backport to stable29

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/53000/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick bdc68989

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/53000/stable29

Error: Failed to check for changes with origin/stable29: No changes found in backport branch

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