PNG sequence export does not match number of animated frames

mmbclip

I’m using Spine 4.2.43.

In the Dope Sheet, I have animated 12 distinct frames (poses) and I want to export them frame-by-frame as a PNG sequence, with exactly the same number of PNG files as the frames I animated.

The issue is that during PNG sequence export, I only get the correct number of images when the export FPS is set to 30. However, even then, the exported sequence often contains duplicate images, and one or more of the frames I animated are not exported at all.

If I lower the export FPS (for example 10, 12, or 15), Spine exports fewer PNG files than the number of frames I animated in the Dope Sheet.

This is for a pixel art workflow. All keyframes are set to Stepped (Stop) curves, so there is no interpolation between frames. Each pose is intentionally static and should be exported exactly once.

My question is:
Is there a way to export every animated pose/keyframe exactly once as a PNG sequence, without time-based resampling, duplicated frames, or skipped frames?

Or is Spine’s PNG export fundamentally time-based, making exact frame-by-frame export impossible for pixel-art-style animations?

Misaki

mmbclip Spinebot's answer is correct. Animation in Spine is time-based, which is why you can create keys for fractional frames like 0.5.

I haven't thoroughly tested this, so I can't be certain it will work perfectly, but besides the solution Spinebot suggested, I think another approach might be to export from Spine as a MOV file using PNG encoding, then export that MOV file as a PNG sequence. This could potentially allow you to accurately obtain each individual frame.

Spinebot

Based on my knowledge of Spine's export system, PNG sequence export is fundamentally time-based, not frame-based. This means Spine always exports based on duration and FPS, not directly on the number of keyframes you've created.

Here's what's happening:

Why you're getting mismatched frame counts:

Spine uses a default timeline of 30 frames per second in the dopesheet. When you have 12 frames animated, that represents:

12 frames ÷ 30 fps = 0.4 seconds of animation

When you export at different FPS rates:

At 30 FPS: 0.4 seconds × 30 fps = 12 images ✓
At 15 FPS: 0.4 seconds × 15 fps = 6 images
At 10 FPS: 0.4 seconds × 10 fps = 4 images

The duplicate/skipped frame issue:

Even when the math works out (like at 30 FPS), you may get duplicates or missing frames because Spine samples the animation at specific time intervals. With stepped curves, if the sampling doesn't land exactly on your keyframes, you might capture the same pose multiple times or miss poses entirely.

Potential workarounds:

Match your export FPS to the timeline FPS (both at 30) - this gives you the best chance of capturing each frame, though duplicates/skips can still occur due to sampling timing.
Adjust animation duration - Place your 12 keyframes so they align perfectly with your intended export FPS. For example, if you want to export at 12 FPS, spread your 12 frames across exactly 1 second (frame 0, 2.5, 5, 7.5, etc. in the 30fps timeline).
Export at higher FPS - Export at a higher frame rate (like 60 or even 120 FPS), then manually select the unique frames from the sequence, discarding duplicates.

Unfortunately, there isn't a built-in "export one PNG per keyframe" option in Spine. The export system is designed for smooth, interpolated animations rather than discrete frame-by-frame workflows.