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WalkthroughWhen stream duration is not positive, ChangesVideo Duration Handling
Priority: ➖ Normal Estimated code review effort: 2 (Simple) | ~10 minutes Severity of issue fixed: Medium Merge Risk: 🟡 Moderate · up to WebM files with container-only duration now decode correctly. However, a crafted file that declares a very large duration can force very large memory allocations before the size limit is checked, which could crash or stall the frontend. Bound the frame count before merging. 🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
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Review comments at @lib/llm/src/preprocessor/media/decoders/video.rs:
- Line 247: In get_num_requested_frames and the caller before get_target_times,
enforce a default global frame-count allocation bound before constructing target
times; use checked arithmetic for proportional allocation sizes and reject
counts that exceed the bound, independent of optional max_frames or num_frames
settings.
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⛔ Files ignored due to path filters (1)
lib/llm/tests/data/media/224p_6_vp9.webmis excluded by!**/*.webm
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lib/llm/src/preprocessor/media/decoders/video.rs
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| } else { | ||
| // WebM may expose duration only at container level, in AV_TIME_BASE units. | ||
| // Clamp unknown (AV_NOPTS_VALUE) or nonpositive durations to zero. | ||
| input.duration().max(0) as f64 / f64::from(ffmpeg_next::ffi::AV_TIME_BASE) |
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🩺 Stability & Availability | 🟠 Major | ⚡ Quick win
🔎 Supported by static analysis
🏁 Script executed:
sed -n '150,420p' lib/llm/src/preprocessor/media/decoders/video.rs
rg -n 'overflow-checks|\[profile' Cargo.toml lib/llm/Cargo.tomlRepository: ai-dynamo/dynamo
Length of output: 10643
🏁 Script executed:
set -o pipefail
printf '%s\n' '--- helper definitions and callers ---'
rg -n -F -- 'fn get_num_requested_frames' lib/llm/src/preprocessor/media/decoders/video.rs
rg -n -F -- 'fn get_target_times' lib/llm/src/preprocessor/media/decoders/video.rs
rg -n -F -- 'get_num_requested_frames(' lib/llm/src/preprocessor/media/decoders/video.rs
rg -n -F -- 'get_target_times(' lib/llm/src/preprocessor/media/decoders/video.rs
printf '%s\n' '--- relevant source ---'
sed -n '1,180p' lib/llm/src/preprocessor/media/decoders/video.rs
printf '%s\n' '--- tests ---'
rg -n -F -- 'max_frames' lib/llm/src/preprocessor/media/decoders/video.rs lib/llm/src/preprocessor/media || true
rg -n -F -- 'num_frames' lib/llm/src/preprocessor/media/decoders/video.rs lib/llm/src/preprocessor/media || true
sed -n '420,760p' lib/llm/src/preprocessor/media/decoders/video.rs
printf '%s\n' '--- Cargo profiles ---'
sed -n '200,245p' Cargo.toml
printf '%s\n' '--- pre-change helper and decode diff ---'
git diff dd2a4301ef02b00f64353c1d81f395b0d0bbb707..3ff14375ab926ee0b9aac1b9ea064b5cba4b1a27 -- lib/llm/src/preprocessor/media/decoders/video.rsRepository: ai-dynamo/dynamo
Length of output: 31034
Bound container-derived frame counts before constructing target times.
When a WebM has no stream duration or frame count, an exaggerated positive container duration can make get_num_requested_frames return a very large count. get_target_times then allocates one Time value per requested frame before the max_alloc check runs. The later allocation expression also uses unchecked multiplication and can wrap in release builds.
Apply the allocation bound before get_target_times. Use checked arithmetic, and reject the frame count before proportional allocations. Optional max_frames and num_frames settings do not provide a default global cap.
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only still-valid issues, skip the rest with a brief reason, keep changes
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Review comment at @lib/llm/src/preprocessor/media/decoders/video.rs at line 247:
In get_num_requested_frames and the caller before get_target_times, enforce a
default global frame-count allocation bound before constructing target times;
use checked arithmetic for proportional allocation sizes and reject counts that
exceed the bound, independent of optional max_frames or num_frames settings.
After applying the fix, consider running `coderabbit review --agent` for local
review. Visit https://docs.coderabbit.ai/cli?utm_source=ghpr
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[P1] One request can get the frontend OOM-killed. video.rs:247. The fallback lets a WebM report a huge frame total, media_io_kwargs can request that many frames, and get_target_times fills 24 bytes per frame first. release/1.6.0-minimax-m3-dev.1 has this change through #14856 and fails the same way. Please run the max_alloc check, with checked multiplication, before get_target_times.
Measured in a running frontend, with steps to reproduce.
The input is a 2-frame VP9 WebM of 7 to 11 KB. Its second frame has a timestamp of 1e9 s. The frontend ran in its own container with --memory=8g --memory-swap=8g, next to a vLLM worker with --frontend-decoding --enable-multimodal (Qwen3-VL-2B).
| image | num_frames 2 |
num_frames 10,000,000 |
num_frames 10,000,000,000 |
|---|---|---|---|
main 8b11b44620 |
500, Cannot determine the video frame count |
same | same, frontend stays up |
release/1.6.0-minimax-m3-dev.1 7f10471620 |
200 | 500, frontend log exceed max alloc, memory peak 225 MB to 466 MB |
empty reply after 2.5 s, frontend container OOMKilled, exit 137 |
#15816 behaves the same, so the fix belongs before get_target_times in decode_video: run the max_alloc check there, with checked multiplication.
-
Make the input. This uses FFmpeg 7.0.2 with libvpx.
ffmpeg -f lavfi -i testsrc2=size=224x224:rate=2 -frames:v 2 \ -vf "setpts='if(eq(N,1),1000000000/TB,PTS)'" -fps_mode passthrough \ -c:v libvpx-vp9 -f webm late_frame.webm -
Start a vLLM worker with
--model Qwen/Qwen3-VL-2B-Instruct --frontend-decoding --enable-multimodal, and a frontend with a memory limit. -
Build the request and send it.
python3 - <<'EOF' > req.json import base64, json b64 = base64.b64encode(open("late_frame.webm", "rb").read()).decode() print(json.dumps({ "model": "Qwen/Qwen3-VL-2B-Instruct", "max_tokens": 8, "messages": [{"role": "user", "content": [ {"type": "video_url", "video_url": {"url": "data:video/webm;base64," + b64}}]}], "media_io_kwargs": {"video": {"num_frames": 10000000000}}, })) EOF curl -s http://localhost:8000/v1/chat/completions \ -H 'Content-Type: application/json' -d @req.json
With num_frames 10000000 instead, the request returns a 500 and the frontend stays up. The frontend log shows Video dimensions 10000000x224x224x3 exceed max alloc 536870912.
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@dmitry-tokarev-nv Thanks for the reproduction and guidance. The supplied code confirms that get_target_times allocates before the max_alloc check. Checked multiplication alone will not prevent that earlier allocation.
- Move decoder setup and dimension validation before
get_target_times. - Calculate RGB allocation sizes with checked arithmetic. Reject overflow and requests above
max_allocbefore constructing target times. - Reuse the validated sizes for the frame buffer.
- Add regression tests for oversized frame requests and arithmetic overflow. Preserve valid sampling behavior.
✏️ Learnings added
Learnt from: dmitry-tokarev-nv
Repo: ai-dynamo/dynamo PR: 15904
File: lib/llm/src/preprocessor/media/decoders/video.rs:247-247
Timestamp: 2026-10-08T21:25:57.134Z
Learning: In the Rust FFmpeg video decoder at lib/llm/src/preprocessor/media/decoders/video.rs, decode_video must enforce the configured max_alloc with checked RGB-size multiplication before calling get_target_times. get_target_times constructs one video_rs::Time per requested frame, so checking only the later RGB buffer allocation does not protect against oversized frame requests derived from untrusted duration metadata.
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| frame_rate.denominator() > 0, | ||
| "Cannot determine the video frame rate" | ||
| ); | ||
| let source_duration = if input_stream.duration() > 0 { |
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When a stream has unknown video duration/frame count but the container duration is positive because of another stream, such as longer audio, this fallback treats the container duration as the video duration. get_num_requested_frames then derives total frame count and target sample times from that longer value; on the default non-strict frontend path the decoder reaches video EOF and returns fewer frames than the requested num_frames/max_frames, while metadata reports the inflated duration. Fall back only to a duration that is known to describe the video stream, or derive the video duration from decoded video packet/frame timestamps before using it for sampling.
🤖 AI Fix
Replace the container-duration fallback with a video-stream duration derived from video packet/frame timestamps, or reject this case until such a video-specific duration is available.
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Confirmed by measurement. The container duration includes the audio, so an ordinary WebM with audio loses samples. A WebM with no container duration still fails before decoding. #15816 decodes all four cases below.
Measured on Linux with the in-tree FFmpeg 9.0.1, default frontend settings (`max_frames` 32, not strict).
| input | this PR | #15816 |
|---|---|---|
| 60 s video and audio, audio ends 8 ms later | 31 of 32 frames. Strict num_frames=3 fails with "2 of 3" |
32 of 32 |
| 30 s video, 60 s audio | 16 of 32 frames, source_duration 60.008. num_frames=3 returns 1 frame |
32 of 32, 30.0 s |
| video starts at 5 s | source_duration 8.0, timestamps 5.0 to 7.5 |
3.0 s, timestamps 0 to 2.5 |
no container duration (-live 1) |
Cannot determine the video frame count |
6 of 6 |
| #[case] num_frames: Option<u64>, | ||
| #[case] expected_frames: usize, | ||
| ) { | ||
| // Finalized six-frame VP9 WebM from the reported data-URL request. |
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This comment mostly repeats the fixture filename and nearby assertions, while the reference to the reported data-URL request is bug-history provenance rather than a lasting constraint needed to understand the test. Remove it or replace it only with non-obvious fixture requirements that are not already asserted below.
🤖 AI Fix
Remove this comment unless you add a concise note about a fixture property that the test does not already express.
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/ok to test 3ff1437 |
✅ Dynamo PR CI passed — run 37808211244 (attempt 1) on
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I believe #15816 supersedes this PR with wider improvement coverage and has gone through a few review rounds |
|
This change already shipped on |
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Previously reported defects still present:
- Original discussion: The PR still derives
requested_framesfrom untrusted container duration and callsget_target_timesbefore applying the decoded-frame allocation limit, so an exaggerated duration can allocate a huge target timestamp vector and the later size calculation still uses unchecked multiplication. Bound the derived frame count before constructing target times and use checked arithmetic for allocation sizing. - Original discussion: The PR still falls back from an unknown video-stream duration to the container duration, so files where another stream controls the container duration can request/sample frames beyond the actual video and report inflated video metadata. Use a duration derived from the selected video stream's packets/frames, or reject this case until a video-specific duration is available.
- Original discussion: The container-duration fallback is still present at the reviewed head and still applies a positive container duration to the selected video stream when the stream duration is unknown. The existing discussion explains that this can use audio or other container duration as the video duration, causing inflated metadata and under-sampling/strict failures.
- Original discussion: The previously raised superfluous-comment concern is still present at lib/llm/src/preprocessor/media/decoders/video.rs:556. The comment mostly repeats the fixture filename and nearby assertions, and the reported data-URL provenance is bug history rather than a lasting constraint needed to understand the test.
- Original discussion: The reviewed head still constructs target times before any allocation-size check, and the allocation-size multiplication remains unchecked. The existing discussion explains that a large container-derived frame count can allocate an oversized target-times vector before the later max_alloc check.
- Original discussion: Verified still present: a positive container duration now feeds get_num_requested_frames before any allocation bound is applied, and decode_video constructs target_times for the resulting requested_frames before checking max_alloc. A file with exaggerated container duration can therefore force a very large Vec allocation independent of the decoded-frame allocation limit. The frame count and arithmetic should be bounded before constructing target_times.
- Original discussion: Verified still present: the fallback at
lib/llm/src/preprocessor/media/decoders/video.rs:242-247uses container duration whenever the selected video stream has no positive duration. That duration is not necessarily owned by the video stream, so WebM files with longer audio or non-zero start offsets can under-sample video frames and report inflated frontend metadata (source_duration, and later Pythontotal_num_frames). The correction is still to derive duration from video packet/frame timestamps or reject the case until a video-specific duration is available. - Original discussion: Verified still present: when stream duration/frame count are unknown, the new container-duration fallback can make
requested_framesarbitrarily large from metadata, andget_target_times(requested_frames, ...)is called before the decoded-frame byte limit atlib/llm/src/preprocessor/media/decoders/video.rs:278-282. A crafted large container duration can therefore force a huge target-time allocation before the existingmax_alloccheck can reject the request. Bound the derived frame count with checked arithmetic before constructing target times or proportional frame buffers. - Original discussion: Verified still present: when the selected video stream lacks duration/frame count, the new fallback uses container duration even when that duration can be determined by another stream or by nonzero stream start time. The resulting source_duration and target sample times can exceed the video timeline, causing the non-strict path to return fewer frames than requested and strict sampling to fail at EOF. The fallback needs to use a video-specific duration or reject this case until one is available.
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Summary
Finalized WebM clips can expose duration only at container level, with unknown video-stream duration and frame count. The frontend currently rejects these before decoding with
Cannot determine the video frame count. Fall back to positive container duration when stream duration is unavailable, converting FFmpeg's time units to seconds and clamping unknown/nonpositive values to zero.Cherry-picks commit
e46c79195aa3b138aa99e4a3e1cbddb0f4c54b14from #14856 ontomain. The only changes are the duration fallback and the exact 846-byte VP9/WebM regression fixture, exercised with all-frame, FPS-based, and fixed-frame sampling.Fixes #15811 for the reported single-video WebM case. Related PR #15816 implements a broader selected-packet timestamp approach. This narrow fallback does not address containers whose audio lasts longer than their video, and inputs without either duration still fail the existing checks. Reviewers should consider the overlap before merging either approach.
Validation
mainplus this commit:cargo test --locked -p dynamo-llm --no-default-features --features media-ffmpeg --lib preprocessor::media::decoders::video::tests— 17 passed, using the Linux FFmpeg 8.1.2 build container.cargo fmt -p dynamo-llm -- --check, pre-commit checks for both changed files, andgit diff --checkpassed.Summary by CodeRabbit