Harden the shared video-audio example

Signed-off-by: Hongsheng Liu <liuhongsheng4@huawei.com>

docs/user_guide/examples/offline_inference/x_to_video_audio.md

@@ -3,7 +3,25 @@
 Source <https://github.com/vllm-project/vllm-omni/tree/main/examples/offline_inference/x_to_video_audio>.
 
 
-The `DreamID-Omni` pipeline generates short videos from text, image and video.
+The shared runner generates video with optional audio from text, image, and audio
+inputs. It can be extended through `vllm_omni.model_extras` without adding
+another model-specific runner.
+
+## Shared request and output contract
+
+The example builds one canonical request envelope: `prompt` is text,
+`modalities` is `["video"]`, and optional `multi_modal_data` contains RGB PIL
+images plus audio `(waveform, sample_rate)` tuples. Audio files are loaded in
+full; the runner does not silently select or crop a time range. Prepare a
+trimmed input file explicitly when only part of a recording should condition
+the model.
+
+Model-specific request translation (for example, DreamID-Omni's two negative
+prompts and its 16 kHz input requirement) is declared in `model_extras`. Model
+outputs must provide `fps` and, when audio is present, `audio_sample_rate`.
+`--fps` and `--audio-sample-rate` are available as explicit metadata overrides.
+The shared encoder normalizes supported video tensor layouts, so this runner
+does not branch on a model name or assume a model-specific frame layout.
 
 ## Local CLI Usage
 ### Download the Model locally
@@ -91,7 +109,8 @@ python x_to_video_audio.py \
 Key arguments:
 - `--prompt`: text description (string).
 - `--model`: path to the model local directory.
-- `--height/--width`: output resolution (defaults 704 * 1024).
+- `--model-class-name`: optional diffusion pipeline class override.
+- `--height/--width`: output resolution (defaults 704 * 1280).
 - `--image-path`: path to the input image list.
 - `--audio-path`: path to the input audio list, indicate the timbre of the output video.
 - `--cfg-parallel-size`: number of parallel cfg parallel (defaults 1).
@@ -101,6 +120,9 @@ Key arguments:
 - `--num-inference-steps`: number of denoising steps (defaults 45).
 - `--video-negative-prompt`: negative prompt for video generation.
 - `--audio-negative-prompt`: negative prompt for audio generation.
+- `--extra-body`: JSON object containing parameters declared by the selected model.
+- `--fps`: explicit output FPS override when a model does not return that metadata.
+- `--audio-sample-rate`: explicit output audio sample-rate override.
 - `--enable-cpu-offload`: enable CPU offload (defaults False).
 
 ## Example materials