fix(preview): ffmpeg gets stuck when getting video cover

[ncheng89]

Summary

Fix the problem of ffmpeg getting stuck when getting the mp4 video cover, set a timeout to prevent the php process from being blocked due to ffmpeg's stuck

fix:#43328

TODO

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)

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