Introduction
This document discusses the overall system delay called In-to-out latency. Properly setting this parameter can help you improve your production's reliability.
IMPORTANT: Every delay mentioned here is counted in frames. So, they are dependent on the rendering frame rate. The higher the rendering frame rate the less the delay's value in seconds for the same value.
In-to-out Latency
In-to-out latency specifies the constant delay the system should try to keep between the incoming video and the final output. This delay includes the delays from:
- the hardware buffers of the input card (SDI or HDMI)
- the software buffers of Aximmetry
- the hardware buffers of the output card
The recommended practice is to adjust the In-to-out latency value to as low as possible without getting any "Cannot keep latency" error. This value will be a hardware-dependent one, you have to find it manually through trial and error.
In-to-out latency can be changed at Edit -> Preferences -> Video Inputs:
In-to-out latency is expressed in frames and specified with a numeric value.
NOTE: You can learn more about frames in the Frame Rate document paragraph.
We can choose between Low and Tolerant presets or we can specify a Custom value.
Input Extra Delay
If multiple video inputs or tracking inputs come along with the video, their arrival times may differ. Even if everything is genlocked, there may be a few milliseconds difference between the actual times of receipt, for different reasons. Aximmetry automatically selects a main input whose framerate is consistent with the current framerate of the system.
- We wait for a frame from the main input to arrive.
- We are waiting some time for the corresponding frame/packet to arrive from the other inputs.
- We render.
The wait time described in step 2 is what you specify in the Input extra delay (expressed as a fractional frame).
Input extra delay is part of In-to-out latency (i.e. not added).
Therefore, when increasing the Input extra delay, we may also need to increase the In-to-out latency. If something is wrong, you will get a red "Cannot keep latency" message in the log, this is what you need to pay attention to.
We can choose between presets for systems where "Every input genlocked", "Some inputs are not genlocked" and "Tracking data is behind video" or we can specify a Custom value.
Negative Delay
Generally, negative delay values should be avoided in Aximmetry (if used incorrectly, the settings will be ignored, and they will not affect production).
Having written this, in certain cases the use of negative delay values is possible.
Negative Tracking Delay
You can use negative delay values for your input devices to the extent of the Input extra delay.
Example of a correct use of negative delay:
Example of an incorrect use of negative delay:
LED productions
Any display device that is directly connected to the DP/HDMI ports of the GPU card, is not affected by the In-to-out latency setting.
These are typically the PC monitors and the LED walls.
These devices display the result directly after the render is finished, without any delay.
Therefore in an LED production, In-to-out latency will only affect the latency of the final SDI out (assuming you use one in Aximmetry). The latency of the LED content itself won't be affected at all, it will be output as fast as possible.
However, Input extra delay can affect it, since rendering won't start until the system is finished waiting for the inputs.
