Second try to get "Support for video file instead of camera and output video out to file" accepted

The old CL can be found here: https://codereview.webrtc.org/2273573003/

The orginal broke down stream, this CL tries to solve those issues.

BUG=webrtc:6545

Review-Url: https://codereview.webrtc.org/2426003002
Cr-Original-Commit-Position: refs/heads/master@{#14665}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 64e1a32e2f3fa790927e71c783520c2d1ed2ead1
10 files changed