[Bugfix][Multimodal] Guard read_frames against empty frame indices - #52102
[Bugfix][Multimodal] Guard read_frames against empty frame indices#52102zuver-lab wants to merge 1 commit into
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Qwen3VLVideoBackend.compute_frames_index_to_sample() returns an empty list
for a 0-frame video (it lacks the base class's max(1, ...) floor), which
crashed VideoBackend.read_frames() with either an IndexError (frame-recovery
path dereferences frame_indices[-1] without the guard applied a few lines
above) or a ValueError from max() of an empty sequence. read_frames is the
single entry point shared by every video backend.
Early-return for empty frame lists, matching the empty-shaped frames the
recovery path already produces for empty input, and add CPU regression tests
covering both frame-recovery modes plus the Qwen3VL zero-frame end-to-end path.
Test:
pytest "tests/multimodal/test_video.py::test_read_frames_handles_empty_frame_indices" \
"tests/multimodal/test_video.py::test_qwen3vl_zero_frame_video_does_not_crash" -v
3 passed
Co-authored-by: Claude <noreply@anthropic.com>
Signed-off-by: kitty <2165990891@qq.com>
![claude[bot]](https://avatars.githubusercontent.com/in/1236702?s=60&v=4){kind=small}
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mergify
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added
multi-modality
| if not frame_idx: | ||
| # Degenerate input (e.g. a video with zero frames): nothing to load. | ||
| # Match the shape produced by the internal readers for empty input. | ||
| width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH)) | ||
| height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT)) | ||
| return np.empty((0, height, width, 3), dtype=np.uint8), [] | ||
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Actually, I think we should reject 0-frame video instead, feeding a 0 frame video to VLM doesn't make sense.
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3 participants
Summary
Qwen3VLVideoBackend.compute_frames_index_to_sample()returns an empty list for a 0-frame video (it lacks the base class'smax(1, ...)floor), which then crashedVideoBackend.read_frames():_read_frames_with_recovery):IndexError: list index out of rangeatnext_target_map[frame_indices[-1]] = total_frames— the same line's neighbormax_frame_idx = frame_indices[-1] if frame_indices else 0is guarded a few lines above, but this one is not.ValueError: max() iterable argument is empty.read_framesis the single entry point shared by every video backend (OpenCV / PyAV / TorchCodec / DeepStream), so the guard protects all of them.This adds an early return for empty frame lists that matches the empty-shaped frames (
np.empty((0, h, w, 3))) the recovery path already produces for empty input — the same state downstream code already receives today for 0-frame videos through the base-class path.Test
ruff check/ruff formaton both changed files: clean.tests/multimodal/test_video.pyrun: 40 passed, 5 skipped; the 25 failures are allModuleNotFoundError: No module named 'av'/'torchcodec'(video decode deps absent in this CPU environment), unrelated to this change.Model evaluation: not applicable — this is a crash-only fix for degenerate (0-frame) input; it does not change output, accuracy, or serving behavior for any valid input.
Duplicate / overlap check
No open PR references an empty-frame crash in
read_framesor the Qwen3VLcompute_frames_index_to_samplepath.DynamicVideoBackendonly, and does not touchread_frames, the Qwen3VL backend, or any backend'sread_framesboundary.bad_words/ YAML-config / JSON-schema empty-input fixes are unrelated code paths.AI assistance
This change was developed with AI assistance (Claude Code): bug identification, fix, and tests were AI-drafted and reviewed by a human before submission.