[Webkit-unassigned] [Bug 194380] New: Running RTCRtpSender.getCapabilities("video") before initial offer breaks VP8

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=194380

            Bug ID: 194380
           Summary: Running RTCRtpSender.getCapabilities("video") before
                    initial offer breaks VP8
           Product: WebKit
           Version: Safari Technology Preview
          Hardware: All
                OS: All
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: WebRTC
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: daginge at confrere.com
                CC: youennf at gmail.com

Affected browser:
Safari Technical Preview Release 75 (Safari 12.2, WebKit 14608.1.3.0.2)

Summary:
If I run RTCRtpSender.getCapabilities("video") before I create the initial peer connection (with offer), VP8 will not be included in the SDP. If I don't run getCapabilities before creating an offer it works as expected.

Steps to reproduce:
1. Open https://webrtc.github.io/samples/src/content/peerconnection/pc1/ in a new tab. Open console upon page load.
2. Click "Start" then "Call"
3. Run pc1.localDescription.sdp.indexOf("VP8") in the console and observe that VP8 is there.
4. Close the browser completely and open https://webrtc.github.io/samples/src/content/peerconnection/pc1/ in a new tab. Open console upon page load.
5. Run RTCRtpSender.getCapabilities("video"). Observe that VP8 is not in the list.
6. Click "Start" then "Call"
7. Run pc1.localDescription.sdp.indexOf("VP8") and see that VP8 is missing (returns -1)

Expected result:
RTCRtpSender.getCapabilities("video") returns VP8 no matter when you call it, and the peer connection always offers VP8 when available.

Actual result:
RTCRtpSender.getCapabilities("video") does not contain VP8 when run before creating initial peer connection, and seems to break VP8 in any following peer connections made afterwards. However, running RTCRtpSender.getCapabilities("video") after the initial offer with VP8 works as expected.

Special thanks to fippo who originally discovered an issue with getCapabilities and aided in debugging the underlying issue.

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