ScheduledFrameCompleted called half the frequency

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Bertrand Drouhard

  • Posts: 9
  • Joined: Sat Jun 20, 2015 7:11 pm

ScheduledFrameCompleted called half the frequency

PostMon Jul 27, 2015 10:27 am


Using the SDK on MacOS, I have an issue with the output callback in my software. It seems to be called half the frequency, making most of the frames to be displayed late or dropped. In bmdModeHD1080p30 mode, the call is made every 65ms and in bmdModeHD1080p24 every 83ms...
Any idea of what can happen ? Thanks for your help ;-)


Nicholas Gill

Blackmagic Design

  • Posts: 169
  • Joined: Mon May 04, 2015 10:28 pm

Re: ScheduledFrameCompleted called half the frequency

PostTue Jul 28, 2015 11:21 pm

Hi Bertrand,

Possible causes for delayed callbacks include,

  • Insufficient CPU resources
  • Application delays in the callback

You've probably already checked CPU resources, could you please advise what actions your application performs in the callback?

The recommendation is that the application perform as little work as possible in the SDK callbacks to ensure that the SDK is able to call the callbacks in a timely manner.

Could you also please clarify which callback? I presume from context you mean IDeckLinkVideoOutputCallback::ScheduledFrameCompleted



Steve Miles

  • Posts: 3
  • Joined: Sat Aug 01, 2015 3:41 pm

Re: ScheduledFrameCompleted called half the frequency

PostSat Aug 01, 2015 3:49 pm

I am seeing this same issue, but am running at 720 p 59.94. I am only getting the callback at roughly 33ms instead of 16 to 17. Some of the callbacks are 40 or 50 ms apart. I do very little in the ScheduleFrameCompleted callback. Basically I just set a flag for the frame generation thread, get and log the elapsed time, and log the result code. My first two frames (which are prescheduled) go out on time. All the rest are late. When I look at recorded video of the output, I am getting duplicated frames on the output (four of each, I think). I am using a ping-pong setup for the generated frames, and am switching and scheduling based on the callback.

I have sufficient CPU resources, and not really anything else going on on the system.

Jonas Geduldig

  • Posts: 20
  • Joined: Tue Jun 17, 2014 7:04 pm

Re: ScheduledFrameCompleted called half the frequency

PostMon Jun 26, 2017 7:01 pm

I'm also running at 720p 5994 and seeing ScheduleFrameCompleted called every 33 ms instead of 16.6 ms. Anyone know what could be the reason for this?

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