How to enable Simulcast in Chrome

[Balwant Bisht]

I am trying to send multiple resolution streams to our MCU using Chrome Simulcast feature but chrome is not enabling the simulcast

OFFER is send by MCU & Chrome reply it with ANSWER

I tried the following

• a=x-google-flag:conference
  

Updated SDP in both direction and added a=x-google-flag:conference in the end

• Adding multiple video tracks with different resolution tracks

Get multiple resolution stream & added tracks in same stream. Then updated ANSWER SDP as following

a=ssrc-group:SIM 120515558 1797338798
a=ssrc:120515558 cname:j0lQUSJ51XrDcoWj
a=ssrc:120515558 msid:5iwUn88sRZCQCuPkJ8V3 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:1797338798 cname:PMukiF+J5RGLtABQVocT7A
a=ssrc:1797338798 msid:dg0KDXz6uLpUDY6M8P3s 36235b69-c1e8-4445-98fa-3845fc7606c6 

a=x-google-flag:conference 

Chrome becomes unresponsive 

• Updating Answer SDP with same video track but different ssrc

a=ssrc-group:SIM 1 2 3
a=ssrc:1 cname:j0lQUSJ51XrDcoWj
a=ssrc:1 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:2 cname:j0lQUSJ51XrDcoWj
a=ssrc:2 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:3 cname:j0lQUSJ51XrDcoWj
a=ssrc:3 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=x-google-flag:conference

 Only seeing ssrc_1_send in chrome://webrtc-internals/

 

[Peter Boström]

Hi, actually not sure whether the setup is wrong or right (my SDP foo is shaky). You can check chrome://webrtc-internals during a Hangouts call if you want to see the SDPs used there. Some answers inline though:

On Sat, Nov 14, 2015 at 6:34 PM Balwant Bisht <balwan...@gmail.com> wrote:

I am trying to send multiple resolution streams to our MCU using Chrome Simulcast feature but chrome is not enabling the simulcast

OFFER is send by MCU & Chrome reply it with ANSWER

I tried the following

• a=x-google-flag:conference
  

Updated SDP in both direction and added a=x-google-flag:conference in the end

• Adding multiple video tracks with different resolution tracks

Get multiple resolution stream & added tracks in same stream. Then updated ANSWER SDP as following

a=ssrc-group:SIM 120515558 1797338798
a=ssrc:120515558 cname:j0lQUSJ51XrDcoWj
a=ssrc:120515558 msid:5iwUn88sRZCQCuPkJ8V3 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:1797338798 cname:PMukiF+J5RGLtABQVocT7A
a=ssrc:1797338798 msid:dg0KDXz6uLpUDY6M8P3s 36235b69-c1e8-4445-98fa-3845fc7606c6 

a=x-google-flag:conference 

Chrome becomes unresponsive 

If you mean that Chrome/the tab hangs, can you please file a bug at https://crbug.com with more details on your setup + how often it repros (flaky/100%?) and link it here?

 

• Updating Answer SDP with same video track but different ssrc

a=ssrc-group:SIM 1 2 3
a=ssrc:1 cname:j0lQUSJ51XrDcoWj
a=ssrc:1 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:2 cname:j0lQUSJ51XrDcoWj
a=ssrc:2 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=ssrc:3 cname:j0lQUSJ51XrDcoWj
a=ssrc:3 msid:0Jr2dOJ9q7P08rHq6QyO69Eln4tLTbjwaNnY 36235b69-c1e8-4441-98fa-3845fc7606c6
a=x-google-flag:conference

 Only seeing ssrc_1_send in chrome://webrtc-internals/

This is not unexpected, we kind of report "per video stream" where simulcast streams are aggregated into one. This can also be seen during a call in Hangouts (in chrome://webrtc-internals). I'd check wireshark/log at the remote endpoint to see which SSRCs are actually transmitted. SRTP doesn't protect the headers, so you can still parse the SSRCs even though the packets are encrypted.

Hope that helps,

- Peter

 

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