moq-gst: fix plugin license + broadcast-aligned timestamps

[kixelated]

Summary

Two small, independent moqsink fixes cherry-picked from the larger rewrite in #1771, without the FLUSH/seek handling or the per-pad/session generation machinery from that PR.

1. Plugin license so the plugin actually loads

GStreamer's registry only loads plugins whose license string is in its recognised set. The plugin_define! license was "Apache 2.0", which is not in that set, so the moq plugin (moqsink/moqsrc) is silently refused at registry load. The crate is MIT OR Apache-2.0, so this declares the MIT side ("MIT/X11"), which is valid.

This commit is self-contained and can be cherry-picked on its own if you want it in faster.

2. Broadcast-aligned timestamps instead of per-pad PTS rebasing

The sink rebased each pad to its own first PTS (reference_pts), zeroing every pad's timeline independently. That breaks A/V alignment: audio and video both start at ~0 regardless of their real offset.

Now the sink forwards the SEGMENT event to the worker and maps each buffer's PTS to GStreamer running time, the broadcast-aligned timeline shared by every pad in the pipeline. It falls back to the raw PTS only when no TIME segment is known (e.g. a BYTES segment).

What this deliberately leaves out (vs #1771)

• FLUSH/seek handling (per-pad watch channels, send_or_flush, re-anchoring). moqsink is a live-publish sink; the flush path adds significant concurrency surface for a case it doesn't exercise.
• Two-level pad/session generation tracking and generation-keyed failure maps.
• The module split and the bounded-channel / error-to-bus changes (separable follow-ups).

Testing

• cargo build -p moq-gst, cargo clippy -p moq-gst --all-targets -- -D warnings, cargo fmt --check, cargo test -p moq-gst all pass (via the nix dev shell).

(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: 19be7b51-ed9c-47a8-b695-4caa4acb2f13

📥 Commits

Reviewing files that changed from the base of the PR and between 230e34d and a7229e5.

📒 Files selected for processing (2)

• rs/moq-gst/src/lib.rs
• rs/moq-gst/src/sink/imp.rs

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Walkthrough

The MoqSink GStreamer plugin gains TIME-segment-aware timestamp mapping. PadState replaces its reference_pts field with an optional gst::FormattedSegment<gst::ClockTime>. A new ControlMessage::Segment variant is added to carry per-pad segment events from the GStreamer thread to the async session worker. handle_event intercepts EventView::Segment events, forwards them via the control channel, then calls the default pad handler. The session worker dispatches the message to handle_segment, which stores the segment only when it is in TIME format. handle_buffer now maps buffer PTS through the stored segment's running-time conversion, falling back to raw PTS if no segment is recorded. Separately, the plugin's license string is corrected from "Apache 2.0" to "MIT/X11" so GStreamer recognizes and loads the plugin.

🚥 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 accurately reflects the two main changes: fixing the plugin license issue and implementing broadcast-aligned timestamps for proper A/V synchronization.
Description check	✅ Passed	The description clearly explains both fixes, the rationale behind each change, and deliberately documents what was excluded from the larger PR #1771.
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/moqsink-license-pts-fix

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