ExeVRM: Execution Video Reward Model

ExeVRM (Execution Video Reward Model) is a fine-tuned Qwen3-VL-8B-Instruct model that judges whether a computer-use agent's video trajectory successfully completes a given task. Given a screen recording of an agent performing a task and a natural language instruction, ExeVRM predicts whether the execution is correct or incorrect.

Model Summary

Key Features: STP & TTP

ExeVRM incorporates two token pruning techniques that enable efficient processing of long execution videos:

• STP (Spatial Token Pruning): Reduces visual tokens within each frame by merging spatially similar patches (e.g., uniform UI backgrounds). Uses connected-component analysis to identify and prune large homogeneous regions.
• TTP (Temporal Token Pruning): Reduces visual tokens across frames by detecting temporally duplicated patches between consecutive frames (e.g., static screen regions between agent actions).

Combined, STP + TTP achieve 40-60% token reduction while maintaining reward prediction quality.

Token Pruning Parameters Used in Training

How to Use

Installation

pip install transformers torch accelerate

For video processing:

pip install av pillow

Loading the Model from Hugging Face

from transformers import Qwen3VLForConditionalGeneration, AutoProcessor
import torch

model_name = "lime-nlp/ExeVRM-8B"  # Replace with the actual HF repo name

# Load model
model = Qwen3VLForConditionalGeneration.from_pretrained(
    model_name,
    torch_dtype=torch.bfloat16,
    device_map="auto",
    trust_remote_code=True,
)

# Load processor
processor = AutoProcessor.from_pretrained(model_name, trust_remote_code=True)

Video Preprocessing

ExeVRM expects 720p (1280x720) video frames sampled at 1 FPS with a maximum of 50 frames. Here is how to preprocess a video:

import av
import numpy as np
import math


def sample_frames_from_video(video_path, fps=1.0, max_frames=50):
    """
    Sample frames from a video at the specified FPS, up to max_frames.

    Args:
        video_path: Path to the video file (mp4, avi, etc.)
        fps: Target frames per second for sampling (default: 1.0)
        max_frames: Maximum number of frames to sample (default: 50)

    Returns:
        List of PIL Images
    """
    container = av.open(video_path)
    stream = container.streams.video[0]

    total_frames = stream.frames
    duration_seconds = float(stream.duration * stream.time_base)

    # Compute number of frames to sample
    sample_frames = max(1, math.floor(duration_seconds * fps))
    sample_frames = min(total_frames, max_frames, sample_frames)

    # Uniformly sample frame indices
    indices = np.linspace(0, total_frames - 1, sample_frames).astype(np.int32)
    indices_set = set(indices.tolist())

    frames = []
    for i, frame in enumerate(container.decode(video=0)):
        if i in indices_set:
            frames.append(frame.to_image())  # Convert to PIL Image
        if i > max(indices):
            break

    container.close()
    return frames

Running Inference

from qwen_vl_utils import process_vision_info

# Prepare the input message
messages = [
    {
        "role": "user",
        "content": [
            {"type": "video", "video": "path/to/agent_trajectory.mp4", "fps": 1.0},
            {"type": "text", "text": (
                "Given a user task and a computer-using video recording, "
                "evaluate whether the user completes the task or not. "
                "Reply your judgement in the \\box{}.\n"
                "If the video correctly completes the task, reply \\box{correct}. "
                "Otherwise, reply \\box{incorrect}.\n\n"
                "# User Task\n"
                "Open Google Chrome and search for 'weather today'\n"
            )},
        ],
    }
]

# Process inputs
text = processor.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
image_inputs, video_inputs = process_vision_info(messages)
inputs = processor(
    text=[text],
    images=image_inputs,
    videos=video_inputs,
    padding=True,
    return_tensors="pt",
).to(model.device)

# Generate
with torch.no_grad():
    output_ids = model.generate(**inputs, max_new_tokens=128)

# Decode
generated_ids = output_ids[:, inputs.input_ids.shape[1]:]
response = processor.batch_decode(generated_ids, skip_special_tokens=True)[0]
print(response)
# Expected output: \box{correct} or \box{incorrect}

Using with qwen_vl_utils (Recommended)

For the most streamlined experience, install the Qwen VL utilities:

pip install qwen-vl-utils

This provides process_vision_info() which handles video frame extraction and formatting automatically, including frame sampling at the specified FPS.

Manual Frame-by-Frame Inference

If you need more control over frame sampling (e.g., for custom preprocessing):

# 1. Sample frames manually
frames = sample_frames_from_video("path/to/video.mp4", fps=1.0, max_frames=50)

# 2. Build message with individual frames as images
content = [{"type": "video", "video": frames}]
content.append({
    "type": "text",
    "text": (
        "Given a user task and a computer-using video recording, "
        "evaluate whether the user completes the task or not. "
        "Reply your judgement in the \\box{}.\n"
        "If the video correctly completes the task, reply \\box{correct}. "
        "Otherwise, reply \\box{incorrect}.\n\n"
        "# User Task\n"
        "Your task description here\n"
    ),
})

messages = [{"role": "user", "content": content}]

# 3. Process and run inference (same as above)
text = processor.apply_chat_template(messages, tokenize=False, add_generation_prompt=True)
image_inputs, video_inputs = process_vision_info(messages)
inputs = processor(
    text=[text],
    images=image_inputs,
    videos=video_inputs,
    padding=True,
    return_tensors="pt",
).to(model.device)

with torch.no_grad():
    output_ids = model.generate(**inputs, max_new_tokens=256)

generated_ids = output_ids[:, inputs.input_ids.shape[1]:]
response = processor.batch_decode(generated_ids, skip_special_tokens=True)[0]
print(response)

Prompt Format

ExeVRM uses the following prompt template for binary reward prediction:

Given a user task and a computer-using video recording, evaluate whether the user completes the task or not. Reply your judgement in the \box{}.
If the video correctly completes the task, reply \box{correct}. Otherwise, reply \box{incorrect}.

# User Task
<task description>

If you want the model output justifications, use the following template instead:

Given a user task and a computer-using video recording, evaluate whether the user completes the task or not. Reply your judgement in the \box{}.
If the video correctly completes the task, reply \box{correct}. Otherwise, reply \box{incorrect}.
If the video does not complete the task (i.e., incorrect), please provide the timestamp range, i.e., from <[time_start] seconds> to <[time_end] seconds>, of the video that deviates from the user's instruction.

# User Task
<task description>

Training Details

• Training Framework: ExeVRM (built on LLaMA-Factory)
• Fine-tuning: Full fine-tuning of the language model; vision tower and multi-modal projector are frozen
• Optimizer: AdamW with cosine learning rate schedule
• Learning rate: 5e-6
• Warmup ratio: 0.1
• Epochs: 1
• Batch size: 1 per device, gradient accumulation steps = 2
• Precision: bfloat16
• Attention: FlashAttention-2
• DeepSpeed: ZeRO Stage 2

Limitations

• The model is trained on computer-use execution videos (desktop/web/mobile). Performance on other video domains is not guaranteed.
• Video inputs should be 720p resolution for best results (matching training distribution).
• The model outputs binary judgments (\box{correct} / \box{incorrect}) and is not designed for open-ended video QA.
• STP and TTP token pruning are applied during training. For inference without the ExeVRM framework, the model processes full video tokens (no pruning), which may require more GPU memory for long videos.

Citation

If you think this model helps your research, please cite the following paper:

@misc{song2026videobasedrewardmodelingcomputeruse,
      title={Video-Based Reward Modeling for Computer-Use Agents}, 
      author={Linxin Song and Jieyu Zhang and Huanxin Sheng and Taiwei Shi and Gupta Rahul and Yang Liu and Ranjay Krishna and Jian Kang and Jieyu Zhao},
      year={2026},
      eprint={2603.10178},
      archivePrefix={arXiv},
      primaryClass={cs.CV},
      url={https://arxiv.org/abs/2603.10178}, 
}

License

Apache License 2.0