SDI capture-overlay-display, what's the best practice?

Ask software engineering and SDK questions for developers working on Mac OS X, Windows or Linux.
  • Author
  • Message
Offline

boyu2022

  • Posts: 3
  • Joined: Tue Aug 23, 2022 3:42 pm
  • Real Name: Bo Yu

SDI capture-overlay-display, what's the best practice?

PostThu Sep 22, 2022 7:12 pm

I'm building a system that has a PC running Ubuntu 18.04 with a DeckLink SDI 4K card installed. The system captures SDI input, adds a bounding box overlay to the frame, then plays the frame out via the output SDI port. I don't have control over the resolution of the SDI input, it could be 1080p30, 1080p25, 1080i60, or 1080i50, and I don't have a reference signal generator to help me synchronize the input and output frames.

My question is, given the constraint of my system, what is the best approach for me to achieve minimal delay between the input and the output frames? Should I use "ScheduleVideoFrame", or "DisplayVideoFrameSync"? The code to add bounding box has negligible delay. I am not worried if the delay is variable or if I occasionally drop a frame, I just want to achieve the lowest overall delay between the input and the output frames.

And a related question, why does using a reference signal help reduce the delays? What is the mechanism behind it? why can't the card just synchronize the output based on the input signal?

Thank you very much for your help!
Offline

Ian Morrish

  • Posts: 580
  • Joined: Sun Jan 18, 2015 9:24 pm
  • Location: New Zealand

Re: SDI capture-overlay-display, what's the best practice?

PostThu Oct 13, 2022 2:32 am

Hi,
The DeckLink SDI 4K has an internal keyer so you can run the card in a mode that just passes the input to output without you having to capture frames.
Assuming you are happy with the output format matching the input (which you say can be unknown but decklink can detect it).

Look for the SDK example folder and "InputLoopThrough" + "LoopThroughWithOpenGLCompositing".

This also results in only one frame of latency and much less processing overhead for your application
Regards,
Ian
Regards,
Ian Morrish
Video Integrated Scripting Environment
(Windows PowerShell with ATEM driver + more)
https://ianmorrish.wordpress.com
Offline

boyu2022

  • Posts: 3
  • Joined: Tue Aug 23, 2022 3:42 pm
  • Real Name: Bo Yu

Re: SDI capture-overlay-display, what's the best practice?

PostTue Nov 15, 2022 3:23 pm

Hi Ian

Thanks for your reply! I just saw this today it's really helpful. Just have a question, if I use the internal keyer can I still get the frame for processing in a parallel thread? Is there documentation on this internal keyer that I could read on?

Thanks again

Return to Software Developers

Who is online

Users browsing this forum: No registered users and 17 guests