LTX, video_run, and framepack_worker bypass process_images_inner, so
they call apply_video_interpolation explicitly before save_video. Save
receives already-inflated frames; the sentinel guard skips its own pass.
- LTX and video_run scale mp4_fps by interpolation_factor(p) so duration
is preserved instead of stretched (LTX is conditioned on source fps)
- FramePack pre-divides at gen time per get_latent_paddings, so save fps
stays at mp4_fps; worker passes p=None so save call uses
mp4_interpolate=0 to skip directly
- replaces the inline (mp4_interpolate+1) fps math at LTX with the
helper-driven equivalent