[Bugfix] Fix handling of encode_video output in vllm.py so each frame’s Base64

[LiamLian0727]

Description:

This PR addresses a bug in the VLLM model integration whereby encode_video() returns a List[str] of Base64‐encoded frames, but the caller treats it as a single string. As a result, the model receives invalid URLs like data:image/png;base64,['AAA','BBB',…].

Summary by CodeRabbit

• Bug Fixes
  • Improved handling of image inputs to prevent errors with non-iterable elements and ensure all images, including those in nested lists or tuples, are processed correctly.

[coderabbitai]

Walkthrough

The flatten method in the VLLM class was updated to handle both iterable and non-iterable elements, ensuring robust flattening of mixed-type inputs. The generate_until method now iterates over the fully flattened list of images, processing all image encodings regardless of input nesting structure.

Changes

File(s)	Change Summary
lmms_eval/models/vllm.py	Improved flatten to handle non-iterables; updated generate_until to process flattened imgs

Sequence Diagram(s)

sequenceDiagram
    participant User
    participant VLLM
    participant Message

    User->>VLLM: Call generate_until(imgs)
    VLLM->>VLLM: flatten(imgs)
    loop For each image in flattened imgs
        VLLM->>Message: Append image URL to content
    end

Loading

Poem

A rabbit hopped through code so neat,
Flattening lists, a tidy feat.
Now images, nested or not,
Are handled well, no error caught.
With every hop, the bugs retreat! 🐇✨

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📥 Commits

Reviewing files that changed from the base of the PR and between ad31c4c and e1bcb88.

📒 Files selected for processing (1)

• lmms_eval/models/vllm.py (2 hunks)

🧰 Additional context used

🧬 Code Graph Analysis (1)

lmms_eval/models/vllm.py (1)

lmms_eval/models/qwen2_5_vl.py (1)

• flatten (173-178)

🔇 Additional comments (2)

lmms_eval/models/vllm.py (2)

153-156: LGTM! Robust handling of mixed input types.

The updated flatten method correctly handles both iterable and non-iterable elements by checking the type before attempting to iterate. This prevents the previous issue where the method would fail if input contained single strings alongside lists/tuples.

The type check using isinstance(i, (list, tuple)) is appropriate and the logic is sound:

• Iterable elements (lists/tuples) are extended into the result
• Non-iterable elements are appended directly

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208-208: Critical fix for Base64 encoding issue.

This change correctly addresses the core issue described in the PR objectives. By using self.flatten(imgs) instead of iterating over imgs directly, each individual Base64 string is now processed separately, preventing the invalid URL format data:image/png;base64,['AAA','BBB',...].

The fix ensures that:

• Single Base64 strings from encode_image() are handled correctly
• Lists of Base64 strings from encode_video() are flattened and each frame is processed individually
• Each frame gets its own properly formatted data URL

✨ Finishing Touches

• 📝 Generate Docstrings

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