# Resolved: Firefox shows up as Black Screen

**URL:** <https://discourse.lynckia.com/t/resolved-firefox-shows-up-as-black-screen/211>\
**Category:** Uncategorized\
**Created:** [October 1, 2014, 12:17pm UTC](https://discourse.lynckia.com/t/resolved-firefox-shows-up-as-black-screen/211 "2014-10-01T12:17:24Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Daniel\_Krax](https://avatars.discourse-cdn.com/v4/letter/d/e5b9ba/32.png) [@Daniel\_Krax](https://discourse.lynckia.com/u/Daniel_Krax)\
**Post date:** [October 1, 2014, 12:17pm UTC](https://discourse.lynckia.com/t/resolved-firefox-shows-up-as-black-screen/211/1 "2014-10-01T12:17:24Z")

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Hi,

We encountered the same problem as  
[https://groups.google.com/d/topic/lynckia/eDJWQujT2dY/discussion](https://groups.google.com/d/topic/lynckia/eDJWQujT2dY/discussion)

[https://groups.google.com/d/topic/lynckia/HD5SFNrcoIQ/discussion](https://groups.google.com/d/topic/lynckia/HD5SFNrcoIQ/discussion)

The solution was actually described there, but we never found the patch.

The short version of this issue:

Firefox publishers show up as black screens.

Changing WebRtcConnection.cpp as here will fix this.

> <https://github.com/K-GmbH/licode/commit/d698d8fd567e33f76ae9af5713c1bd0f426342c7>

The long version:

WebRtcConnection read the video SSRC from RTP packets when the source was a  
firefox publisher. It also cast RTCP packets as RTP packets for this. The  
result is that the bytes 12 to 15 of a RTCP Sender Report were interpreted  
as SSRC despite those being part of a timestamp. When the first packet was  
RTP, the algorithm actually had the right video SSRC, but when the first  
packet was RTCP the wrong video SSRC was retrieved.

This resulted in Firefox publish streams not properly reacting to RTCP  
feedback because a wrong video SSRC was used. The actual cause for the  
black screen was that Firefox rejected the Picture Loss Indicator (PLI)  
because it was sent for a wrong video SSRC.

The fix addresses the issue by checking the packet type for RTCP and  
reading the video SSRC from the correct position. It also prevents  
overwriting the timestamp in RTCP packets and only sets the video SSRC if  
the packet is RTP.

The fix might solve a lot more issues with Firefox since it now uses the  
correct video SSRC. Chrome publishers were never affected since they  
provide the video SSRC in the SDP.

Best regards,

-Daniel