TROUBLESHOOTING: What does "Video card buffer underrun" means

If you see this logs in the Activity and Logs window of your favorite Softron ingest or playout:

! 2016-02-21 16:11:14 Monday Camera 1 1080i59.94: Error: Video card buffer full (dropped 1 frames)

This is shown when we can't transfer the frames quickly enough to/from the video device. Frames are transferred as "uncompressed" from the device, and thus this requires a lot of bandwidth. The video devices have a buffer of a few frames to accommodate some temporary slow downs, but if the slowdown is longer than the buffer then

  • for ingest applications, the video device may "throw away" some video frames before they have a chance to get transferred to MovieRecorder. These frames are thus completely lost.
  • for playout applications, the video device does not have enough frames to maintain the output fps, and will thus duplicate the last frames it has until a new one is available.

This type of issue can be caused by various things. Below are the most common issues.

 

The bandwidth to access the video device is too slow

Some devices offer the ability to run a test to check the connection speed to the device. This can be done with AJA System Tests (for AJA devices) and with dCARE (for Deltacast devices). If it's a Thunderbolt device, make sure that nothing can slow it down. Common causes can be:

  • another device is connected on the same BUS and is using too much bandwidth, thus limiting what we can get from the device
  • you have connected another device on the same BUS that uses a slower protocol. If you connect a Thunderbolt 2 device to the same BUS as another Thunderbolt 3 device, both devices will be at the Thunderbolt 2 speed.
  • what is requested is simply too much for what the Thunderbolt can do. For, Thunderbolt 2 can accommodate 8 channels of 1080i59.94 in 8 bit, but not in 10 bit, there is simply not enough bandwidth in the PCIe protocol of Thunderbolt 2. Get in touch with us if you have any questions regarding bandwidth requirements over Thunderbolt.

 

Computer or software hangs or slow downs

On a computer there are many processes running at the same time. One of them may cause some system hangs or slow downs. Open the Activity Monitor application and when the issue happens, check all applications:

  • CPU usage
  • Memory usage

If any application uses too much resources, there might not be enough left for your Softron application, and if we are slowed down in our process, we won't be able to send or retrieve frames quickly enough from/to the device.

 

Hardware issue

It could also be a hardware issue. Either:

  • the Computer itself
  • a specific port/BUS on that computer
  • the Thunderbolt cable,
  • the Sonnet box (if any)
  • or the video device itself

Try to replace the components you can. Cables are the easiest, try to change Thunderbolt port and BUS, etc...

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