Skyrim SE .hkx animations are not being recognized by the game

[Needgit]

Hi there, I am trying to replace some animations in Skyrim SE, but when the animation should get played in Skyrim, the character will simply T-pose instead. I also attempted to preview the animation in the Creation Kit, but that lead to a crash of the editor.

I've been following the instructions from Basic Workflow and there seems to be no issue with importing/exporting in Blender, and I have attempted with Blender 5.0.1 and 4.5.8 LTS without any errors in the Blender console - but both results in the same T-pose.

I've added an example blend file, along with the original .hkx animation and skeleton used and the exported .hkx file here: skyrim_animation.zip
The animation that it is replacing is located at "...\Data\meshes\actors\character\animations\swimidle.hkx"
All extracted files are from "Skyrim - Animations.bsa"

I've also attempted to use purely LE original files and then converting them using Cathedral Assets Optimizer, but that will result in the same. And I've attempted by using the Legacy Workflow.

I've tried replacing different animations as well, and none of them seem to work.

It seems that the original and exported file are very different in content which leads me to believe that there is something wrong with the file export data. Either that, or I am missing something completely.

I'm using the latest PyNifly V25.11.

[Needgit]

Update on working with the Legacy Workflow. It seems that PyNifly actually do fail which just means that the previous export was not overwritten, and thus my test was incomplete.

Here is the console output:

====================================
PYNIFLY EXPORT HKX V25.11.0


INFO:pynifly:Created temporary kf file: C:\Users\XXXXX\AppData\Local\Temp\tmp_swimidle_07BDC9.kf
ERROR:pynifly:HKXCMD failed with error:
ERROR:pynifly:Export of HKX failed
Traceback (most recent call last):
  File "C:\Users\XXXXX\AppData\Roaming\Blender Foundation\Blender\4.5\scripts\addons\io_scene_nifly\hkx\export_hkx.py", line 279, in execute
    self.write_annotations()
  File "C:\Users\XXXXX\AppData\Roaming\Blender Foundation\Blender\4.5\scripts\addons\io_scene_nifly\hkx\export_hkx.py", line 162, in write_annotations
    xmlfile = xml.parse(self.xml_filepath)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Program Files\Blender Foundation\Blender 4.5\4.5\python\Lib\xml\etree\ElementTree.py", line 1219, in parse
    tree.parse(source, parser)
  File "C:\Program Files\Blender Foundation\Blender 4.5\4.5\python\Lib\xml\etree\ElementTree.py", line 570, in parse
    source = open(source, "rb")
             ^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: 'C:\\Users\\XXXXX\\AppData\\Local\\Temp\\tmp_swimidle.xml'
INFO:pynifly:

PyNifly EXPORT of swimidle.hkx completed WITH ERRORS
====================================

I'm was trying to see if I could find out what was going on by looking at the python code, and it seems that hkxcmd is not executing the conversion from .kf to .hkx. This causes a cascade of errors later on, which is why the error is about an .xml file, but rather, the error occurred earlier...

That behavior is similar to an experiment I did myself, by trying to export using PyNifly to .kf instead of directly .hkx. Then I used hkxcmd.exe to attempt to convert, but the program did not do anything, not even creating an error. Nothing was outputted. It seems that the .kf format might be broken?

Also regarding that, I found another bug related to exporting .kf. On line 117 in 'export_kf.py', there is a small mistake, which is:

self.rename_bones_niftools = pyniflyPrefs.rename_bones_nift

should be (I think):

self.rename_bones_niftools = pyniflyPrefs.rename_bones_niftools

Correcting this and reloading the scripts in Blender allowed me to export. Otherwise blender came up with an error and suggested the rename to pyniflyPrefs.rename_bones_niftools.

Bonus info:
It seems that if I export to Skyrim LE .hkx and attempt to use Bethesda's HavokBehaviorPostProcess tool (in ...\Skyrim Special Edition\Tools\HavokBehaviorPostProcess) - that program could read the .hkx and output an SE version. However, this outputted version causes the game to CTD.

I've tried other converters such as Composite HKX Conversion GUI, but that is not able to read the generated .hkx from PyNifly. That is why it is kinda interesting that Bethesda's tool can 🤔

[BadDogSkyrim]

Are you forced to use the legacy workflow for some reason? I'm highly include to remove it entirely. The whole process of fumbling through multiple steps is bound to be fragile.

[Needgit]

Are you forced to use the legacy workflow for some reason? I'm highly include to remove it entirely. The whole process of fumbling through multiple steps is bound to be fragile.

No, I am not forced to use the legacy work flow. I would much rather use the new actually :)
I simply tried various methods to see if I was doing something wrong.

But I think that in my trying I may have found an issue in the .kf exporter - since 'hkxcmd' will not convert them to .hkx, neither using the blender export to .hkx (generate_hkx() in 'export_hkx.py') or by manually using the 'hkxcmd' tool.

On another note, since I may not have been clear about it... The example that I posted in the OP is a test where I do not perform any modifications to the animation. It is simply an import of a skeleton and an animation, and then exported - yet, the original file and the exported file differs in binary content - and maybe that is the issue for both .hkx and .kf...

I'm curious if you are able to replace animations on your setup?

[BadDogSkyrim]

I have... but the particular animations I looked at may not have shown the issues.

[BadDogSkyrim]

Yup, bug confirmed. Working on it.

[BadDogSkyrim]

Fixed in V25.12.

[Needgit]

Fixed in V25.12.

That you so much for looking into this. I can confirm that the animations will play now :D
But for some reason, the FPS now defaults to 24 FPS in the blender export settings and it seems that Skyrim assumes 30. Of course there is a work around here, to simply set it manually to 30, but it is annoying to do that every time...

But I also found a very strange edge case for a particular animation that causes CTD after finishing playing. Specifically it is the animation "...\Data\meshes\actors\character\animations\dlc01\special_dlc01coffinexit.hkx"

If that animation is replaced by any other animation that is exported from PyNifly, then the game will CTD after the animation finishes playing. If it is replaced by an animation directly extracted from Skyrim's own .bsa, then it gets replaced and will not CTD. So I think that there is something strange with the exported animations that might cause the CTD.

Do you want to continue using this issue for the new discovered CTD edge case or do you want me to create a new one? After all, I think this issue in of itself has been resolved, and could be closed :)

Edit:
Actually, there was one more detail... The above assumes using the new workflow, which now makes the animation play in the game, but using the legacy workflow, I found the same error as described earlier. Also, no matter which workflow is used, no other tool will parse the exported .hkx files. So if I try to export to Skyrim LE, and then want to use 'hkxcmd' or 'Cathedral Assets Optimizer' to upgrade the format for Skyrim SE, then those programs will not parse the exported file.

[BadDogSkyrim]

That suggests there's still something not quite right in what I'm exporting. Keep this issue open and I'll have a look. That animation interacts with the coffin, right, to open the lid? If so I might need to figure out paired animations which I've kind of punted on.

For the fps issue, set your Blender fps in scene or render (forget which) to 30 and the importer and exporter should honor that.

[Needgit]

Thank you for looking into it. I did some further investigation to see if I would find a workaround, by extracting for Skyrim LE and then try to convert those to SE and found something interesting.

It seems that the animation called "special_dlc01coffinidle.hkx" can be converted to SE format using 'hkxcmd' even after being exported by PyNifly, but "special_dlc01coffinexit.hkx" could not. I also tried the "swimidle.hkx" from earlier but that one is also unable to be converted. The tool simply quietly gives up. This was of course tested with LE exported animations, so that they could be converted to SE.

Then I found, that the size of the exported animations were in general larger than their original .bsa version, and it seems that the animations that are not able to be converted actually are all very large compared to their original. Here are some for comparison: anims.zip (original .bsa extract for LE and LE export from PyNifly).

Then I tried to run the original .bsa extracted animation for LE and ran it through these commands:

./hkxcmd.exe CONVERT -V:XML special_dlc01coffinexit.hkx anim.xml

And then:

./hkxcmd.exe CONVERT -V:XML anim.xml out-LE.hkx

This, interestingly enough, creates an "out-LE.hkx" that is around 213 KB, where the original "special_dlc01coffinexit.hkx" file was only around 57,6 KB.

Then lastly:

./hkxcmd.exe CONVERT -V:AMD64 out-LE.hkx out-SE.hkx

Then, after that, the file size of "out-SE.hkx" will be around 58,5 KB which is exactly the same as the .bsa extract from SE - which is expected.

This might be a complete red herring, but the reason why I think this is interesting is that the size from converting from XML and to hkx matches more the larger file size that PyNifly exported (does not matter if export to LE or SE for this). I was thinking that maybe, the new workflow uses some similar conversion principles as for the XML->hkx.

Key takeaways:

1. I'm working on SE so the only reason I look at LE was to find a workaround for the CTD, but instead I found this.
2. "special_dlc01coffinidle.hkx" (PyNifly exported to LE) can be opened by 'hkxcmd'
3. "special_dlc01coffinidle.hkx" (PyNifly exported to LE) has a file size that is comparable to its original .bsa verison
4. "special_dlc01coffinexit.hkx" and "swimidle.hkx" (PyNifly exported to LE) and maybe others as well cannot be opened by 'hkxcmd'
5. "special_dlc01coffinexit.hkx" and "swimidle.hkx" (PyNifly exported to LE) has a larger file size than their original .bsa verison
6. Converting from LE -> XML -> LE yields a larger .hkx file size than the original
7. Converting from LE -> XML -> LE -> SE yields a similar file size as the original SE .bsa verison

[BadDogSkyrim]

There's a number of reasons the file sizes could be different. More bones exported (even though they don't move relative to their parent bone), more frames, whatever. I'll see what I can see.

[BadDogSkyrim]

So I don't have LE loaded up and I'd rather not, though I suppose if LE animations aren't working I'll have to.

I ran all those anims through a blender import/export and they all seem to work just fine in SE. I test them by renaming them "sneakmtidle.hkx" and going into sneak in game. It's an easy way to trigger them.

I can't get anything out of hkxcmd. I'll have a look at that.

[BadDogSkyrim]

Wait a minute. Of course not. hkxcmd is LE-only. So I'm not sure there's a real issue here.

[Needgit]

Wait a minute. Of course not. hkxcmd is LE-only. So I'm not sure there's a real issue here.

I haven't tested much with Skyrim LE either, I just exported to LE in order to test with the 'hkxcmd' tool but then ran into this issue...

But I think that if PyNifly's LE exports can't work with the official tools, that maybe there is a hint in that? But I agree, it is not my biggest pain point either - that is the CTD issue.

I ran all those anims through a blender import/export and they all seem to work just fine in SE. I test them by renaming them "sneakmtidle.hkx" and going into sneak in game. It's an easy way to trigger them.

I also tried replacing with various animations and I agree that they seem to play correctly. If I do what you suggest, then the exported "special_dlc01coffinexit.hkx" animation will play nicely if replacing "sneakmtidle.hkx".

But for some reason "special_dlc01coffinexit.hkx" will always crash after playing no matter what exported animation I replace it with.
I mean the reverse of what you suggested to do, example: take an exported "sneakmtidle.hkx" and override the "special_dlc01coffinexit.hkx" animation. Then the sneak animation will play when exiting the coffin, but then CTD once it is finished.

If I replace "special_dlc01coffinexit.hkx" with an original .bsa animation - for example replaced "special_dlc01coffinexit.hkx" for the original "swimidle.hkx", then it seems to work without CTD. But it always CTD when using the PyNifly exported animations.

If you want to get an "easy" way to test the scene yourself, then, this is the sequence of commands I issue to get there (and then I make a save before opening the coffin):

setstage DLC1VQ00 200
setstage DLC1VQ01MiscObjective 10
setstage DLC1VQ01MiscObjective 180
setstage DLC1VQ01 10
coc DLC1DimHollowCrypt02

You can just kill the vampires with the 'kill' command, but be careful about using 'killall' since that also kills Serana in the coffin.

I hope I am not info overloading here - or start to look like the conspiracy guy meme 🙃
My issue is still about the CTD issue and not specifically the 'hkxcmd' tool. You are probably right regarding the paired/furniture animation that you mentioned before.

[BadDogSkyrim]

No worries, just debugging here. I'm upgrading skeleton I/O, will check this when that's done.