Bug 194380 – Running RTCRtpSender.getCapabilities("video") before initial offer breaks VP8

• Component: WebRTC
• Status: RESOLVED FIXED

[Dag-Inge Aas]

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.

[Radar WebKit Bug Importer]

<rdar://problem/47916514>

[youenn fablet]

Created attachment 361508 [details]
Patch

[EWS Watchlist]

Attachment 361508 [details] did not pass style-queue:


ERROR: Source/WebCore/platform/mediastream/libwebrtc/LibWebRTCProvider.h:116:  Inline functions should not be in classes annotated with WEBCORE_EXPORT. Remove the macro from the class and apply it to each appropriate method, or move the inline function definition out-of-line.  [build/webcore_export] [4]
Total errors found: 1 in 9 files


If any of these errors are false positives, please file a bug against check-webkit-style.

[WebKit Commit Bot]

Comment on attachment 361508 [details]
Patch

Clearing flags on attachment: 361508

Committed r241200: <https://trac.webkit.org/changeset/241200>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.