Video length and frame rate

Frames, length, fps: the numbers each video model expects.

#In plain words

• Frames: how many pictures the clip has. Set by length (built-in nodes) or num_frames (WanVideoWrapper).
• Frame rate (fps): how many frames play per second. Set on Create Video. It does not change what is drawn, only how fast it plays.
• Duration = frames ÷ fps. 81 frames at 16 fps is about 5 seconds.

Each model was trained at one frame rate and up to a certain length. The VAE packs several frames into one latent frame, so the frame count must fit a pattern: for Wan and HunyuanVideo 4n + 1 (49, 81, 121), for LTX 8n + 1 (97, 121).

#Numbers per model

#What changes when you change it

• More frames: longer clip, more memory and time (roughly in proportion), and more risk that faces and figures drift towards the end. Beyond the trained length quality falls fast.
• Another fps on Create Video: the clip plays faster or slower than the model meant; motion looks sped up or slow.
• Longer scenes are made of several clips, by continuing from the last frame, or with pack nodes that work in windows (InfiniteTalk, Wan Animate's frame_window_size).
• Smoother playback comes from frame interpolation after generation (for example RIFE or FILM nodes from packs), not from a higher fps field.

#Typical mistakes

• length 80 instead of 81: ComfyUI rounds to the pattern, and the clip is shorter than expected.
• fps 24 on a Wan 14B clip: motion too fast.
• A driving video at another frame rate than the model: wrong speed of motion.

#How the app helps

The video lessons accept length and num_frames from 49 to 121 and check fps 16, 23, 24 or 25 as the model needs.

#See also

• Video generation
• Resolution and aspect ratio
• Graphics card memory
• Latent