FEC-13956: Add window before MediaSource

[MosheMaorKaltura]

Description of the Changes

Please add a detailed description of the change, whether it's an enhancement or a bugfix. If the PR is related to an open issue please link to it.

CheckLists

• [ ] changes have been done against master branch, and PR does not conflict
• [ ] new unit / functional tests have been added (whenever applicable)
• [ ] test are passing in local environment
• [ ] Travis tests are passing (or test results are not worse than on master branch :))
• [ ] Docs have been updated