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FFMPEG & Decklink Delay

PostPosted: Sat Jun 27, 2020 9:50 pm
by bounce
I have noticed when decoding with a decklink card using ffmpeg there is a noticeable 4 second delay before video starts playing in linux. Is there any way to improve this? Since we are using live streaming... The delay makes it unbearable for our project.

I know it is the decoder because another decoder shows at most a 2 second delay. Any ideas, suggestions?

I saw something like bmdtools is an option and its possible to pipe the output into that? Is this an option for linux? Anybody tried this?

Can any developers weigh in on a possible remedy?

Re: FFMPEG & Decklink Delay

PostPosted: Fri Jul 17, 2020 6:05 am
by deadsound
We have tried the -probesize 32 -analyzeduration 50 and -fflags nobuffer. We can get it sub 2 seconds, but it is inconsistent and next time you start it it will be at 4 again. Also looking for answers...gstreamer we can get sub 1 second video performance...

Re: FFMPEG & Decklink Delay

PostPosted: Tue Jul 28, 2020 1:03 pm
by jzampieron
Have you tried other capture devices? How are you streaming?

There are many factors which influence video latency, including compression codec settings, jitter buffers and similar.

Without understanding your entire setup it will be hard to guide your debugging.

Re: FFMPEG & Decklink Delay

PostPosted: Thu Jul 30, 2020 3:58 pm
by deadsound
I am using decklink quad 2 for output device...but have tried decklink 8k pro and others with the same result using FFMPEG.
Example code:
ffmpeg -re -rtsp_transport tcp -i rtsp://xxxxxx/live/test -ar 48000 -probesize 32 -analyzeduration 40 -rtbufsize 0 -f decklink -pix_fmt uyvy422 -s 1920x1080 88:a3f351e3:00000000
Using OBS NVNEC @ 60 fps as streaming source to nimble server.... other encoder side settings do not have an effect as we get 4 seconds of latency...

I have also tried rtmp streams and it has basically the same result.

I can use the same hardware and OBS streaming config and when using gstreamer we can get sub second delay. Also using OBS built in tools we get very low latency when using the BM seems lots of people have the issue when doing a google search for FFMPEG and decklink...just have not found the soultion. thx