[Frando]

The moq-video side is moq-dev/moq#4023.

#3 is on main (squash 8398528). Rebased onto that, so this PR is only feat: open the first render node that offers what a codec needs and perf: decode into an exported surface again once the consumer drops it.

Problem

• The encoder and the decoder open /dev/dri/renderD128 unless told otherwise. A machine with two GPUs numbers its render nodes in probe order, so an Intel or AMD device behind an NVIDIA one sits on renderD129 and neither opens.
• Exporting a decoded picture retires its surface from the pool for good. A decoder feeding a renderer therefore allocates a new VA surface for every picture and destroys the old one when the consumer lets it go.

Approach

• encode::Config::device and decode::Config::device become Option<PathBuf>. None, the new default, opens the first render node whose driver offers the entrypoint the codec needs; the error names every node passed over and why. A named node is used or refused, never swapped for another. Encoder::config reports the node picked. Processor::open uses the same search, and DrmDeviceIterator skips a missing node instead of stopping at it.
• encode::probe, decode::probe and vpp::probe are public so a caller can find one node that does everything, which is what moq-video does to keep a decoded picture, its resize, and its encode on one device.
• The DPB and an ExportedFrame share the surface behind an Arc, and it returns to the pool when the last of them drops, from whichever thread. A picture the consumer holds is still never decoded over. The pool is held weakly, so a frame that outlives its decoder or sequence releases its surface to the driver. The pool keeps at most a full DPB plus one picture free and destroys any surface returned past that, so a consumer that held many pictures and let them go at once does not leave them parked.

Impact

• encode::Config::device and decode::Config::device change type from PathBuf to Option<PathBuf>, and both default to None rather than renderD128.
• New: encode::probe, decode::probe, vpp::probe.
• DrmDeviceIterator yields nodes after a gap.
• Dropping an ExportedFrame now returns its surface to the decoder, which decodes into it again. A consumer has to keep the frame until nothing reads the descriptor or an import of it; the docs say so.

Validation

On Intel Meteor Lake with iHD, cargo test --lib (31 tests, all running on the hardware), cargo clippy --all-targets -- -D warnings, and cargo fmt --all --check.

• a_dropped_export_is_decoded_into_again exports 60 pictures, dropping each after comparing its read-back with a second decoder's download. It allocated 60 surfaces before this change and 2 after. At 1080p the wall time per picture was 2.4 to 3.3 ms before and 2.2 to 2.7 ms after over three runs, which is within the noise of the decode.
• the_pool_keeps_a_bounded_number_of_free_surfaces holds 40 pictures, drops them, and checks what the pool keeps and that later pictures reuse it.
• the_render_node_is_found_or_named covers the search and a named node that is not a render node.

This machine has only renderD128, so the search past an unsuitable first node is untested on hardware.

Alternatives

• Bounding the surfaces on loan instead (failing or blocking the decode when a consumer holds too many). The old iroh-live decoder did that with a fixed pool and it turned transient backlog into decode errors, so this bounds only what the pool keeps.
• An environment variable here for the node. The override belongs to the application, so the crate takes a path and moq-video reads its own variable.

Follow-ups

• ExportedFrame::from_surface pictures, the VPP resize output, are still allocated per frame; a pool in Processor would fix that.

(Written by Claude Opus 5.5)

🤖 Generated with Claude Code

(Written by Grok 4)

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Walkthrough

The crate adds color-space metadata, DRM DMA-BUF import, and VA-API video post-processing. The encoder accepts CPU NV12 and DMA-BUF input, supports conversion and scaling, and allows bitrate changes between frames. Render-node selection now probes available devices when no path is configured. Decoder surfaces use a bounded, shareable recycling pool, and exported frames can wrap external NV12 surfaces.

Merge Risk: 🔵 Low · up to 018f0

This change adds DMA-BUF import, GPU post-processing, render-node discovery, and decoder surface reuse. One narrow problem remains. On drivers that do not advertise packed SPS/PPS headers, the encoder still sends them on every keyframe. That could make keyframe encoding fail, or produce streams with duplicate headers, on some non-Intel drivers. Merging is reasonable if the owners accept this risk, but the fix is small.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 86.87% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 99 functions across 8 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly summarizes the two primary changes: render-node selection by codec entrypoint and recycling exported decode surfaces.
Description check	✅ Passed	The description directly explains the device-selection and decoded-surface-reuse changes, including their motivation, implementation, impact, and validation.

✨ Finishing Touches 💡 1

⚔️ Resolve merge conflicts 💡

• Resolve merge conflict in branch pr/vaapi-hygiene

✨ Simplify code

• Create a new PR

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Actionable comments posted: 1

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• 🪄 Fix CodeRabbit comments on this PR

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Inline comments:
In `@src/encode.rs`:
- Around line 189-197: Store the negotiated packed-header bitmask from
`packed_headers` in an `Encoder` field, initializing it in `Encoder::new`. In
`encode_surface`, submit the packed SPS and PPS buffers on IDR frames only when
their respective sequence and picture bits are set, so unaccepted header kinds
are not submitted.

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📒 Files selected for processing (9)

• README.md
• src/codec/h264/parser.rs
• src/color.rs
• src/decode.rs
• src/display.rs
• src/dmabuf.rs
• src/encode.rs
• src/lib.rs
• src/vpp.rs

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[kixelated]

Rebased onto main after #3 landed as 8398528, so only the two commits that belong here remain. just ci passed locally (clippy, fmt, 31 lib tests, cargo deny) before the push.

Squash-merged. The packed-header note from review is unchanged code from #3, left for a follow-up.

(Written by Grok 4)