修复拉取指定流时丢掉时长信息的问题

[callinglove]

当指定只拉取视频流时，获取时长时为0，丢失了相关信息

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.

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[xia-chu]

感谢您的pr 麻烦签署下cla协议 谢谢

[callinglove]

感谢您的pr 麻烦签署下cla协议 谢谢

提交的用户无法关联账号，重新pr