Minimising Latency
Posted: 25 Jul 2013, 14:33
On a recent show using Ventuz, my client supplied me camera feeds from some Sony HD Camcorders with an SDI output. The cameras fed a Panasonic HD vision mixer, and I then took the feed into Ventuz. My system was top spec with AMD W8000, S400 sync card and Deltacast HDSDI card. I know in the past we have had about 2.5 to 3 frames of latency through our system depending on input.
The lipsync was very close to being unacceptable for a live awards show. I suspect that the cameras were probably a frame and a half to two frames delayed out of the SDI, as from experience I have found camcorders have quite a bit of internal processing going on, adding to the delay. We tried all sorts from running the system at standard def rates, 720p/25 720p/50 and 1080i with appropriate changes to the native vision mixer rate. Unfortunately I have found that camera suppliers are not interested in genlocking their cameras to a house sync anymore, preferring to just use the frame stores in the vision mixers. Of course, if this is just fed directly to a Plasma or LCD screen, you can get away with it! Unfortunately adding a Ventuz input/output and a projector just tips it over the edge. The brain seems quite happy to have about 2 frames of delay without noticing it!
Nothing seemed to improve the latency, and in the end we were helped by the audio engineer adding a couple of frames of delay to make the lip sync look acceptable (just) and the audio not too much like a train station announcement for the presenter.
When you add in the delay in the projectors (professional Christie HD units) we found that in an ideal world, we had to delay by 200ms to get everything absolutely spot on. This is just not achievable in a real world situation, as while the audience view at the rear of the room (about 60 metres from the stage) would look correct with live camera, the front row view of the live camera image would be very wrong as they could hear the un-amplified voice of the presenter.
I came across this Nvidia input card while searching for details on the new, and not yet released K6000 graphics output card...
http://www.nvidia.com/object/quadro-dig ... eline.html
I was wondering if this is (1) supported by Ventuz, and (2) an improvement on the standard Deltacast input and AMD/Nvidia output card scenario as regards reducing the amount of latency?
Regards
Peter
The lipsync was very close to being unacceptable for a live awards show. I suspect that the cameras were probably a frame and a half to two frames delayed out of the SDI, as from experience I have found camcorders have quite a bit of internal processing going on, adding to the delay. We tried all sorts from running the system at standard def rates, 720p/25 720p/50 and 1080i with appropriate changes to the native vision mixer rate. Unfortunately I have found that camera suppliers are not interested in genlocking their cameras to a house sync anymore, preferring to just use the frame stores in the vision mixers. Of course, if this is just fed directly to a Plasma or LCD screen, you can get away with it! Unfortunately adding a Ventuz input/output and a projector just tips it over the edge. The brain seems quite happy to have about 2 frames of delay without noticing it!
Nothing seemed to improve the latency, and in the end we were helped by the audio engineer adding a couple of frames of delay to make the lip sync look acceptable (just) and the audio not too much like a train station announcement for the presenter.
When you add in the delay in the projectors (professional Christie HD units) we found that in an ideal world, we had to delay by 200ms to get everything absolutely spot on. This is just not achievable in a real world situation, as while the audience view at the rear of the room (about 60 metres from the stage) would look correct with live camera, the front row view of the live camera image would be very wrong as they could hear the un-amplified voice of the presenter.
I came across this Nvidia input card while searching for details on the new, and not yet released K6000 graphics output card...
http://www.nvidia.com/object/quadro-dig ... eline.html
I was wondering if this is (1) supported by Ventuz, and (2) an improvement on the standard Deltacast input and AMD/Nvidia output card scenario as regards reducing the amount of latency?
Regards
Peter