Bug 195489 – [Safari 12.1 Beta] Adding a previously removed MediaStreamTrack does not change direction from "recvonly" to "sendrecv"

• Status: RESOLVED
• Resolution: CONFIGURATION CHANGED
• Component: WebRTC

[Manjesh Malavalli]

Steps to reproduce:

1. Open this JSFiddle: https://jsfiddle.net/9uk4a8b6/ in a new tab.
2. Observe the browser console.

Expected behavior:

The "video" m= section's direction should be "sendrecv".

Actual behavior:

The "video" m= section's direction is "recvonly".

Effect:

The remote RTCPeerConnection does not emit an RTCTrackEvent for the re-added MediaStreamTrack.

Note:

The same JSFiddle runs correctly in the current stable version of Chrome.

[youenn fablet]

Hi Manjesh,

we are currently moving out plan B and going to Unified plan.
Your existing test is setting plan B, is it plan B specific?
Do you experience the same issue with unified plan?

[Manjesh Malavalli]

Hi Youenn,

My understanding was that Safari 12.1+ will support unified plan. But I was surprised that the Safari 12.1 Beta4, on which I ran the JSFiddle was using plan b SDPs and exhibiting this behavior. I have not seen this behavior in the latest Safari Tech Preview (12.2), which does indeed support unified plan.

Can you let me know where I can get access to the latest Safari 12.1 Beta with unified plan support?

Thanks,

Manjesh

[Manjesh Malavalli]

Hi Youenn,

On my dev machine, Safari 12.1 uses "plan-b" SDPs by default and "unified-plan" support  has to be enabled by going to "Develop" > "Experimental features". Are you planning to make "unified-plan" the default in 12.1?

Thanks,

Manjesh

[Manjesh Malavalli]

Hi Youenn,

I created another JSFiddle: https://jsfiddle.net/0c4utdfm/ to run the same scenario with unified plan turned on. This issue is reproducible in unified plan mode as well.

Thanks,

Manjesh

[youenn fablet]

Looking more closely at the jsfiddle, it seems to be doing the following thing:
- It is adding a track. At that point, the corresponding transceiver/m-section is sendrecv 
- It is removing the track. At that point, the corresponding transceiver/m-section is made recvonly
- It is adding the same track. At that point, this creates a new transceiver/m-section for this track. The transceiver/m-section related to the removed track is not reused for the addTrack call so it stays as recvonly.

I think this matches the intended behavior.
Can you confirm this?

[Manjesh Malavalli]

Hi Yoenn,

In "unified plan" mode on Safari 12.1 Beta4, I compared the behavior with that of Chrome and Firefox and looks like it matches expected behavior.

However, the local copy of Safari 12.1 Beta4 that I have installed on my machine has "plan-b" as the default SDP format. And in "plan-b" mode, the "video" m= section does not switch back to "sendrecv" after re-adding the MediaStreamTrack.

Can you confirm that you will be setting "unified plan" as the default SDP format in Safari 12.1? It is really important to us that we know which version of Safari will support "unified plan" as the default SDP format as we are trying to coincide out SDK releases with Safari's rollout.

Thanks,

Manjesh

[Radar WebKit Bug Importer]

<rdar://problem/48790953>

[youenn fablet]

Unified plan is on by default.