"Failed to start output. It's possible that encoder doesn't start." Error on youtube RTMP


New Member
Hi guys,
I get the above error when using multiple RTMPs to stream a webinar. This appears to only be for youtube RTMPs and appears fix if I switch back to using x264 encoder instead of "NVIDIA NVENC h.264 (New)".

Again the error only applies to youtube - I output to several facebook RTMPs, and two instagrams via yellowduck.

I assumed using NVENC would allow me to use my GEFORCE GTX 1660 which was sort of the whole reason I just bought the system.

Additional info is that when I try to stream by just pressing "Stream" in the OBS interface - instead of via the RTMP Buttons - I get an error which states:

"NVENC Error: Too many concurrent sessions. Try closing other recording software....etc etc".

Any help on this would be great. Meanwhile I'm guessing I switch back to x264 for youtube...?

Log file attached.


  • 2021-09-01 11-11-58.txt
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New Member
Just as an addition to this I changed the sequence in which I log into the various RTMP buttons and it actually changed the fault. It appears that I can ONLY output to 3 RTMP buttons using NVENC, after that the RTMP Buttons only work if I use the x264 encoder in the button setting.
Quite odd as I have a huge graphics card and it's not maxing out at all per the performance monitor.