视频播放退到后台耗电严重

**Describe the bug**
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**To Reproduce**
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1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

**Expected behavior**
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**Screenshots**
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**Desktop (please complete the following information):**
- OS: [e.g. iOS]
- Browser [e.g. chrome, safari]
- Version [e.g. 22]

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
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Issue #707 provides no reproduction steps, platform, version, files, or tests beyond the report that background video playback consumes excessive power. Start by obtaining those missing details and reproducing playback in the foreground and background on a specified supported platform. Done should be defined by a verified reduction in background power use without breaking playback.

Written by the indexing model from the issue text.