mp4a: find esds inside the QuickTime wave box

[AdrianEddy]

Problem

Mp4a::decode_body has a comment saying "Find esds in mp4a or wave", but it never actually descends into the QuickTime wave box — it only iterates the direct children of mp4a. When the esds is nested inside a wave (siDecompressionParam) box, the loop sees wave as an unknown atom, skips it via decode_unknown, and then returns Error::MissingBox(esds), failing the whole moov decode.

This is a very common layout: FFmpeg's mov muxer and many camera apps (e.g. MotionCam) emit AAC-in-MOV with the esds inside wave:

mp4a
  wave                       // siDecompressionParam
    frma  'mp4a'
    mp4a  (4-byte stub)      // NOT a valid AudioSampleEntry
    esds
    0000  (all-zero terminator)

Such files currently fail to parse entirely with missing box: esds.

Fix

Descend into the wave box and scan its children by header for esds (and btrt), which is what the existing comment already promised. Every other child — frma, the nested mp4a terminator stub, the trailing zero box — is skipped by size and deliberately not typed-decoded: the nested mp4a is a 4-byte stub that is not a valid audio sample entry, so decoding it as one would error.

The change is additive and does not affect the ISO-BMFF path (esds as a direct child of mp4a). Re-encoding normalises to the ISO layout, as before.

Test

Adds test_mp4a_quicktime_wave, which builds the QuickTime mp4a → wave → { frma, mp4a-stub, esds, terminator } layout and asserts Mp4a::decode recovers the esds. Full suite passes (227 tests).

[coderabbitai]

Walkthrough

Updated Mp4a::decode_body to handle QuickTime wave containers. A new helper scans nested atoms, decoding esds and btrt entries while stopping on invalid sizes. Added a test helper and unit test covering nested AAC atoms and validating the decoded audio fields.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is concise and accurately summarizes the main change: finding esds inside QuickTime wave boxes.
Description check	✅ Passed	The description is directly related to the change and clearly explains the problem, fix, and test coverage.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/moov/trak/mdia/minf/stbl/stsd/mp4a/mod.rs`:
- Around line 134-198: In test_mp4a_quicktime_wave, move audio_bytes directly
into mp4a_body instead of cloning it. Also extend the wave fixture with a btrt
child and assert the decoded result preserves the expected bitrate data,
covering decode_wave’s btrt handling.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

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Configuration used: Organization UI

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Run ID: bfb205fa-6378-42ed-b8cb-ad7562b048d2

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Reviewing files that changed from the base of the PR and between 3241814 and 11ad4b7.

📒 Files selected for processing (1)

• src/moov/trak/mdia/minf/stbl/stsd/mp4a/mod.rs

[bradh]

@coderabbitai full review

[coderabbitai]

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Full review finished.

[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@src/moov/trak/mdia/minf/stbl/stsd/mp4a/mod.rs`:
- Around line 68-85: Update the size guard in decode_wave so only child sizes
greater than zero and within wave.remaining() are accepted. Treat Some(0) like
other invalid or over-long sizes by breaking the scan, ensuring
wave.advance(size) always makes progress.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 2bf5cc98-1306-46d0-be12-31e7ca41de8f

📥 Commits

Reviewing files that changed from the base of the PR and between 3241814 and d073717.

📒 Files selected for processing (1)

• src/moov/trak/mdia/minf/stbl/stsd/mp4a/mod.rs