[cherry-pick releasev0.18.0post1] Codex/release v0.18.0.post1 cherry-pick #2735/#2736/#2555 (#2813)

Signed-off-by: samithuang <285365963@qq.com>
Signed-off-by: David Chen <530634352@qq.com>
Signed-off-by: Samit <285365963@qq.com>
Signed-off-by: david6666666 <530634352@qq.com>
Co-authored-by: Samit <285365963@qq.com>

docs/user_guide/examples/online_serving/text_to_video.md

@@ -123,6 +123,9 @@ curl -X POST http://localhost:8091/v1/videos \
   -F "guidance_scale_2=4.0" \
   -F "boundary_ratio=0.875" \
   -F "flow_shift=5.0" \
+  -F "enable_frame_interpolation=true" \
+  -F "frame_interpolation_exp=1" \
+  -F "frame_interpolation_scale=1.0" \
   -F "seed=42"
 ```
 
@@ -145,6 +148,35 @@ curl -X POST http://localhost:8091/v1/videos \
 | `flow_shift`          | float  | None    | Scheduler flow shift (Wan2.2)                    |
 | `seed`                | int    | None    | Random seed (reproducible)                       |
 | `lora`                | object | None    | LoRA configuration                               |
+| `enable_frame_interpolation` | bool | false | Enable RIFE frame interpolation before MP4 encoding |
+| `frame_interpolation_exp` | int | 1 | Interpolation exponent; 1=2x temporal resolution, 2=4x |
+| `frame_interpolation_scale` | float | 1.0 | RIFE inference scale; use 0.5 for high-resolution inputs |
+| `frame_interpolation_model_path` | str | None | Local directory or Hugging Face repo ID with `flownet.pkl`; defaults to `elfgum/RIFE-4.22.lite` |
+
+## Frame Interpolation
+
+Frame interpolation is an optional post-processing step for `/v1/videos` and
+`/v1/videos/sync`. It synthesizes intermediate frames between generated frames
+without rerunning the diffusion model. If the generated video has `N` frames,
+the interpolated output frame count is `(N - 1) * 2**exp + 1`. The encoder FPS
+is multiplied by `2**exp` so the output duration remains close to the original.
+
+Frame interpolation runs in the diffusion worker post-processing path instead of
+the API server encoding path, so it can reuse the worker's current accelerator
+device without blocking the FastAPI event loop.
+
+Example: generate 5 frames and interpolate to 9 frames:
+
+```bash
+curl -X POST http://localhost:8091/v1/videos/sync \
+  -F "prompt=A dog running through a park" \
+  -F "num_frames=5" \
+  -F "fps=8" \
+  -F "enable_frame_interpolation=true" \
+  -F "frame_interpolation_exp=1" \
+  -F "frame_interpolation_scale=1.0" \
+  -o sync_t2v_interpolated.mp4
+```
 
 ## Create Response Format