> For the complete documentation index, see [llms.txt](https://shaheerxansari.gitbook.io/hydroportdoc/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://shaheerxansari.gitbook.io/hydroportdoc/mrq-and-motion-blur.md).
# MRQ & Motion Blur
HydroPort is built to render baked fluid animation in Sequencer and Movie Render Queue (MRQ), using Alembic velocity data when available.
{% stepper %}
{% step %}
## Prepare the sequence
1. Import the cache with correct **Velocity Units**, **Velocity Scale**, and **Import Velocities** enabled.
2. Add the HydroPort Actor to a Level Sequence.
3. Add the **Fluid Cache** track, set the section range, and check playback settings.
4. Add a **Cine Camera Actor**, set up the shot, and include the relevant camera cut track.
{% endstep %}
{% step %}
## Configure Movie Render Queue
Open MRQ for your Level Sequence and configure output format, resolution, and desired render quality.
For the developer's tested fluid motion-blur workflow:
| Setting | Starting recommendation |
| ------------------------- | ------------------------------------------------------------------------------------------------------- |
| **Spatial Sample Count** | **1** |
| **Temporal Sample Count** | Increase above 1 as appropriate for the shot and render cost |
| **Camera shutter timing** | **Frame Close**, rather than Frame Center, to mitigate the ghosting observed in this HydroPort workflow |
{% hint style="warning" %}
**Important distinction:** More **temporal samples** provide denser sampling across the shutter interval; they do not by themselves change the physical motion-blur shutter duration. Your chosen shutter parameters, velocity data, and rendering method affect blur appearance.
{% endhint %}
{% endstep %}
{% step %}
## Recommended Ghosting Fix: Frame Close
In MRQ settings, the **Camera →** **Shutter Timing → Frame Close** instead of **Frame Center** removes motion-blur ghosting in their tested HydroPort scenes.
{% hint style="info" %}
**Use it as the recommended HydroPort starting point**, not as a guarantee that every kind of ghosting is impossible. Unusable Alembic velocities, wrong velocity scales, scene lighting, camera motion, and temporal accumulation can also influence artifacts.
{% endhint %}
{% endstep %}
{% endstepper %}
## How HydroPort motion vectors work
The Alembic cache can provide velocities (motion rate in source units per second). HydroPort converts them to its internal **centimeters per second**, then derives the previous-frame displacement used by Unreal's Geometry Cache vertex factory:
```
MotionVector = -VelocityInCentimetersPerSecond × SecondsPerFrame
SecondsPerFrame = 1 / AlembicFPS
```
This is the convention used in `HydroMeshComponent.cpp`. The custom renderer provides explicit deformation motion vectors instead of relying only on rigid-object motion.
For example, with correctly converted velocity of 240 cm/s at 24 FPS, the nominal displacement magnitude is `240 / 24 = 10 cm` per cache frame; the stored motion-vector direction follows the implementation's negative-sign convention.
## Troubleshooting Blur
* **No visible deformation blur:** confirm the Alembic exported velocity data and the **Import Velocities** flag.
* **Blur too strong or too weak:** verify the source velocity units, **Velocity Scale**, **Alembic FPS**, and shutter configuration.
* **Ghosting:** first try **Frame Close** and compare rendered frames; also check velocity validity and temporal settings.
* **Viewport differs from MRQ:** editor preview and final exact-frame evaluation use different scheduling approaches.
## Final Render Checklist
* [ ] Correct velocity scaling
* [ ] Play Alembic Animation enabled
* [ ] Fluid Cache track added and spanning the desired frames
* [ ] Cine Camera / Camera Cuts configured
* [ ] Spatial samples = 1
* [ ] Temporal sample count selected for the shot
* [ ] Shutter Timing = Frame Close
* [ ] A short test render inspected before the full sequence
