USD

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.usd export & render


If you want to export .usd files to render frames (like .ifd or .ass), then you should modify your USD ROP node.

The USD ROP does not contain any information about the frame name 
nor does it contain an information which renderer you want to use

nor any override for a rendersettings node (in case you want to switch between test and production render)


Modify the nodes interface (add spare parameter)








Important Note:
These settings do not change the exported .usd file in any way!
They are just informations for Royal Render.
Royal Render tells the Houdini commandline render and render setting and which output file it should generate.




Nested Usd/Alembic files


If you are using other .usd or alembic files as a reference to your new .usd, then you might get some issues.

To add files by reference, simply add a reference node to your /stage.



Motion Blur

If you want to use Motion Blur, then you have to export a single alembic/usd file with all animation.
(and not a file per frame)
Note: You can use usdstichclips to create a single .usd file from a per-frame usd sequence.
(It does not copy the data into the new file, it creates reference links. See next section "FPS issues" as well.)



FPS issues

After importing an all-frame single .usd file, you might get the warning you might get a warning on a node saying 
"Time codes per second metadata is inconsistent across time dependent inputs. Composition may not be as expected."

Explanation:
Somtimes .usd files might miss the FPS information. 
And if this information is missing, the USD file is 24FPS by default.
Importing this into a 25FPS Houdini scene creates some issues.

Origin:
If you export single all-frame a .usd file, then it might contain a FPS information set by a render properties node in your scene.

But you often want to create a per-frame .usd sequence (because you wanted to use multiple machines to render it or because it saves space on fileserver cache nodes).
The disadvantage of this per-frame .usd sequence is that you cannot use Motion Blur.
So you need to use the usdstichclips rop node to create a single all-frame .usd file (with references to your per-frame usd sequence).

And this new .usd file it does not specify a framerate. 
So USD/lops assume it is in 24 FPS regardless of what the Houdini scene is set to. 
The only way to fix it is to export the stitched USD as a .usda file and ingest the 25 fps tag yourself.

Note: 
This will be fixed according to SideFX in the future.
Current release when this help section was written: 19.0.561