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Dropped frames in h264 file

General discussion about anything TouchDesigner

Dropped frames in h264 file

Postby hypnokevin » Tue Jun 12, 2018 9:21 am

I'm using a Blackmagic Quad 2 to capture three streams of 1080p24. These go through a Switch TOP, so I choose one stream at a time, into a moviefileout using h264 (also set to 24fps). Sometimes, one or two of the streams will drop maybe half the frames in the h264 file. (It's interesting that when it happens, it happens to a stream, not the entire video file or portions of it in time.) I'm also monitoring these streams on-screen when it happens, and I swear I don't notice the frame rate drop live -- it seems to be only in the h264 file.

This happened for an installation last month and somebody suggested it was because my i7 only had 16 PCIE lanes, which wouldn't be enough to capture all the video streams and use a GTX 1080 ti as well. This sounded reasonable, so I got an AMD Threadripper 1950x machine with 64 PCIE lanes and the same thing happens (still using the Blackmagic Quad 2 and a 1080 ti).

Does anybody have any clever ideas? I have access to the machine tomorrow to try and debug this before it goes live again. I think I noticed that the Blackmagic inputs show up under the WDM driver, so maybe I'll try that. Setting a constant bitrate on the encoder didn't help... I'm kind of at a loss!
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Re: Dropped frames in h264 file

Postby malcolm » Tue Jun 12, 2018 11:54 am

Is TD running at 24FPS, and is your monitor 24FPS? TD will sync to the monitor's refresh rate by default, so even if TD is set to 24FPS, if your monitor is 60hz then it won't be able to properly run at 24FPS.
There is an option to turn off V-Sync in the Window COMP, so if you go into Perform mode then you can run TD at 24FPS on a 60hz monitor.
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Re: Dropped frames in h264 file

Postby hypnokevin » Tue Jun 12, 2018 4:09 pm

Thanks, that's good advice. I'll give it a shot.
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