qtdemux: Allow a sample for multple output streams

A sample of meta item (such as an image) can be also other stream's sample.
14 jobs for heif-support in 70 minutes and 11 seconds (queued for 28 seconds)
Status Job ID Name Coverage
  Preparation
passed #257396
gst indent

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manifest

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  Build
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build fedora x86_64

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build nodebug fedora x86_64

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  Test
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check fedora

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integration testsuites fedora

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  Full Builds
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build cerbero android universal

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build cerbero cross win32

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build cerbero cross win64

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build cerbero fedora x86_64

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  Full Tests
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valgrind bad

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valgrind ges

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valgrind good

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  Apps
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android universal examples

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