gstreamer: add VP8 and VP9 codec support

[kixelated]

Summary

Adds VP8 and VP9 support to the GStreamer plugin (moqsink / moqsrc). H.264, H.265, AV1, AAC, and Opus were already wired up, and the VP8/VP9 importers already exist in moq-mux, so this is purely plumbing the GStreamer caps through to them.

Changes

• moqsink (publish) — accept video/x-vp8 and video/x-vp9 sink pads and map them to FramedFormat::Vp8 / Vp9. Like AV1, they initialize with an empty buffer since VP8/VP9 carry no out-of-band config; the track is created lazily from the first keyframe's inline dimensions.
• moqsrc (subscribe) — emit video/x-vp8 / video/x-vp9 caps for VP8/VP9 catalog entries. No codec_data is attached since the decoders parse profile/bit-depth from the bitstream itself.
• docs — added VP8/VP9 rows to the supported-codecs table in doc/bin/gstreamer.md (per the Cross-Package Sync rule).

Reviewer notes

• VP8 and VP9 were the only video codecs missing; all audio codecs (AAC, Opus) were already present.
• On the source side I attach no codec_data for VP9, so the catalog's vpcC config record isn't propagated into the GStreamer caps. vp9dec / decodebin3 parse the needed config from the bitstream, so this works in practice. If strict caps negotiation is later desired, we could translate vpcC → the profile / bit-depth caps fields.

Test plan

• cargo build -p moq-gst — clean
• cargo clippy -p moq-gst (via nix to match CI toolchain) — clean, no warnings
• End-to-end VP8/VP9 publish → subscribe round-trip with a real GStreamer pipeline

(Written by Claude)

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: de7b791d-212b-4164-b050-56c94b714c87

📥 Commits

Reviewing files that changed from the base of the PR and between cec6fc4 and b0369d2.

📒 Files selected for processing (3)

• doc/bin/gstreamer.md
• rs/moq-gst/src/sink/imp.rs
• rs/moq-gst/src/source/imp.rs

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Walkthrough

This PR adds VP8 and VP9 video codec support to the moq-gst GStreamer elements. The sink element's capability template was extended to advertise video/x-vp8 and video/x-vp9, with corresponding handler logic that allocates frame buffers and instantiates the appropriate moq_mux::import::FramedFormat decoders. The source element's video_caps function now generates matching VP8/VP9 capabilities. Documentation of supported moqsink codecs was updated to reflect these additions.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely summarizes the main change: adding VP8 and VP9 codec support to GStreamer plugin, which is the central objective across all file modifications.
Description check	✅ Passed	The description comprehensively explains the changeset, detailing VP8/VP9 additions to moqsink, moqsrc, and documentation, with context on related codecs and design rationale.
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.

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✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch claude/suspicious-hellman-aa6849

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