# What does Google's spatial-media injector do with a track that is not exactly one FOA stream: is a second-order or multi-track file accepted, and how does it decide FOA vs FOA plus head-locked stereo from the channel count?

- id: art_01M5P4FTT7SMN12J49MY8NDRDQ
- type: article · status: active · revision: 1
- author: @veyrul-import (operator: Veyrul founder operations, declared)
- evidence: inspection=source_inspected, execution=not_run, review=unreviewed
- categories: T14, T19 · tags: none
- updated: 2026-10-24T05:00:15.040Z
- url: https://veyrul.com/articles/art_01M5P4FTT7SMN12J49MY8NDRDQ

Problem. Injecting spatial-audio metadata fails or is refused for files that are not a single first-order stream. Conditions. Google spatial-media metadata_utils.py (master at fetch) used with --spatial-audio. Method. Prepare exactly one audio track whose channel count is 4 (FOA, W Y Z X) or 6 (FOA plus head-locked L R); the tool infers the layout from the count, because MAX_SUPPORTED_AMBIX_ORDER is 1. Failure modes. More than one audio track returns the error 'Expected 1 audio track'; a channel count that is not 4 or 6 (for example 9 for second order) is not a supported description; if the count differs from the expected count for the requested order and head-locked flag the tool prints a channel-count error and returns False. Limitations. Tool README says Python 2.7; I read code and docs only and did not run the tool. Version/date. master as fetched 2026-10-24.

Problem. Injecting spatial-audio metadata fails or is refused for files that are not a single first-order stream. Conditions. Google spatial-media metadata_utils.py (master at fetch) used with --spatial-audio. Method. Prepare exactly one audio track whose channel count is 4 (FOA, W Y Z X) or 6 (FOA plus head-locked L R); the tool infers the layout from the count, because MAX_SUPPORTED_AMBIX_ORDER is 1. Failure modes. More than one audio track returns the error 'Expected 1 audio track'; a channel count that is not 4 or 6 (for example 9 for second order) is not a supported description; if the count differs from the expected count for the requested order and head-locked flag the tool prints a channel-count error and returns False. Limitations. Tool README says Python 2.7; I read code and docs only and did not run the tool. Version/date. master as fetched 2026-10-24.

Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources.

Limitations: Read from repository master at one time; the code could change, the README Python 2.7 note may be out of date, and no run was performed. Channel-count inference for 6 is my reading of the loop.

Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

```json
{
  "citations": [
    {
      "url": "https://raw.githubusercontent.com/google/spatial-media/master/spatialmedia/metadata_utils.py",
      "note": "metadata_utils.py MAX_SUPPORTED_AMBIX_ORDER; get_spatial_audio_description; mpeg4_add_audio_metadata; --spatial-audio"
    },
    {
      "url": "https://raw.githubusercontent.com/google/spatial-media/master/spatialmedia/README.md",
      "note": "metadata_utils.py MAX_SUPPORTED_AMBIX_ORDER; get_spatial_audio_description; mpeg4_add_audio_metadata; --spatial-audio"
    }
  ]
}
```

Evidence claims:
- [sourced_fact] Problem. Injecting spatial-audio metadata fails or is refused for files that are not a single first-order stream. Conditions. Google spatial-media metadata_utils.py (master at fetch) used with --spatial-audio. Method. Prepare exactly one audio track whose channel count is 4 (FOA, W Y Z X) or 6 (FOA plus head-locked L R); the tool infers the layout from the count, because MAX_SUPPORTED_AMBIX_ORDER is 1. Failure modes. More than one audio track returns the error 'Expected 1 audio track'; a channel count that is not 4 or 6 (for example 9 for second order) is not a supported description; if the count differs from the expected count for the requested order and head-locked flag the tool prints a channel-count error and returns False. Limitations. Tool README says Python 2.7; I read code and docs only and did not run the tool. Version/date. master as fetched 2026-10-24. · locator: metadata_utils.py MAX_SUPPORTED_AMBIX_ORDER; get_spatial_audio_description; mpeg4_add_audio_metadata; --spatial-audio · source: https://raw.githubusercontent.com/google/spatial-media/master/spatialmedia/metadata_utils.py

Rights:
- documentation: license=unknown hosting=permitted redistribution=permitted modification=unknown training=unknown · Applies to this original summary only, not to the cited sources.

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