A stem (isolated track component). Top-level leaf (FM-549 s38: pulled out from under release.* ; release.stem -> stem). May optionally reference a parent track and/or a parent stems-group.
tid
Timestamp-based ID
Properties
aiDeclaration
object
Optional
Declaration of AI involvement in creation
audioDurationMs
integer
Required
Duration of the stem in milliseconds
audioFormat
string
Required
Audio file format
maxLength: 100 byteswav, flac, mp3audioHash
string
Required
SHA-256 hash of the stem audio content
maxLength: 200 bytesaudioSizeBytes
integer
Required
Size of the audio file in bytes
audioUrl
string
uri
Optional
DEPRECATED (FM-508): no longer emitted. Stem audio is private (gated download / app-served preview) and is never surfaced in the portable record. Field kept (optional) to tolerate pre-FM-508 records without a putRecord rewrite. Stems never get a public clip.
maxLength: 3000 bytesbpmCentis
integer
Optional
Centi-BPM (BPM × 100), integer — the Lexicon model has no float type; decode as `bpmCentis / 100` on read. Mirrors `fm.freemix.release.track`.
minimum: 2000maximum: 99900coverArtUrl
string
uri
Optional
URL to cover art image
maxLength: 3000 bytescreatedAt
string
datetime
Required
Record creation timestamp
maxLength: 100 bytesdescription
string
Optional
Stem description
maxLength: 5000 bytesdetachedAt
string
datetime
Optional
FM-504 tombstone: when the parent link was severed
maxLength: 100 bytesgenres
array
of
string
Optional
Genre classifications. Deliberately plural `genres` (it IS an array), NOT the track lexicon's singular `genre` — singular-for-an-array is misleading. Intentional divergence.
maxLength: 10 itemslabel
string
Required
Human-readable name (e.g., 'Main Vocal', 'Acid Line', '808 Kit')
maxLength: 100 byteslicense
string
at-uri
Optional
AT URI of the license grant record. For child stems this is the parent track's license, copied down at creation (FM-504)
maxLength: 3000 bytesmusicalKey
string
Optional
Musical key (e.g., 'Am', 'F#m', 'Bb'). Deliberately named `musicalKey`, NOT the track lexicon's `key`: `key` is dangerously overloaded in a data layer (record keys, rkeys, map keys), so `musicalKey` is collision-proof and self-documenting. Intentional divergence.
maxLength: 10 bytesnotes
string
Optional
Generic freeform notes for this stem (FM-550, s41). Any purpose — processing notes, licensing caveats, or an ad-hoc credit like 'Drummer: Joey Beats'. Deliberately NOT the structured #trackCredits block: most credit roles are meaningless on a stem, so a freeform escape hatch covers the rare case. Stems carry no structured credits.
maxLength: 1000 bytesparentGroup
string
at-uri
Optional
AT URI of the parent fm.freemix.group.stems this stem belongs to (optional). FM-549 s38: stems may carry an optional parentTrack AND an optional parentGroup back-ref — the only upward refs in the model (containers otherwise point down at members).
maxLength: 3000 bytesparentGroupCid
string
cid
Optional
CID of the parent stems-group record (pins to exact version).
maxLength: 200 bytesparentTrack
string
at-uri
Optional
AT URI of the parent track this stem belongs to (optional for standalone stems)
maxLength: 3000 bytesparentTrackCid
string
cid
Optional
CID of the parent track record (pins to exact version)
maxLength: 200 bytesposition
integer
Optional
Display order position (0-indexed)
minimum: 0previouslyAttachedToCid
string
cid
Optional
FM-504 tombstone: CID of the former parent track record at detach time
maxLength: 200 bytespreviouslyAttachedToUri
string
at-uri
Optional
FM-504 tombstone: AT URI of the former parent track, set when this stem was detached (parent deleted, keep-stems path). Preserves remix-tree placement + royalty-lineage reconstructability
maxLength: 3000 bytesstemType
string
Required
Type/category of the stem
maxLength: 100 bytesdrums, bass, vocals, synth, guitar, keys, pad, lead, fx, othertags
array
of
string
Optional
Freeform tags
maxLength: 10 itemstitle
string
Optional
Stem title (first-class stems). `label` remains the required human-readable name; `title` is the unified-on-title field added in FM-504
maxLength: 300 bytesView raw schema
{
"key": "tid",
"type": "record",
"record": {
"type": "object",
"required": [
"stemType",
"label",
"audioHash",
"audioDurationMs",
"audioFormat",
"audioSizeBytes",
"createdAt"
],
"properties": {
"tags": {
"type": "array",
"items": {
"type": "string",
"maxLength": 50
},
"maxLength": 10,
"description": "Freeform tags"
},
"label": {
"type": "string",
"maxLength": 100,
"description": "Human-readable name (e.g., 'Main Vocal', 'Acid Line', '808 Kit')"
},
"notes": {
"type": "string",
"maxLength": 1000,
"description": "Generic freeform notes for this stem (FM-550, s41). Any purpose — processing notes, licensing caveats, or an ad-hoc credit like 'Drummer: Joey Beats'. Deliberately NOT the structured #trackCredits block: most credit roles are meaningless on a stem, so a freeform escape hatch covers the rare case. Stems carry no structured credits."
},
"title": {
"type": "string",
"maxLength": 300,
"description": "Stem title (first-class stems). `label` remains the required human-readable name; `title` is the unified-on-title field added in FM-504"
},
"genres": {
"type": "array",
"items": {
"type": "string",
"maxLength": 50
},
"maxLength": 10,
"description": "Genre classifications. Deliberately plural `genres` (it IS an array), NOT the track lexicon's singular `genre` — singular-for-an-array is misleading. Intentional divergence."
},
"license": {
"type": "string",
"format": "at-uri",
"maxLength": 3000,
"description": "AT URI of the license grant record. For child stems this is the parent track's license, copied down at creation (FM-504)"
},
"audioUrl": {
"type": "string",
"format": "uri",
"maxLength": 3000,
"description": "DEPRECATED (FM-508): no longer emitted. Stem audio is private (gated download / app-served preview) and is never surfaced in the portable record. Field kept (optional) to tolerate pre-FM-508 records without a putRecord rewrite. Stems never get a public clip."
},
"position": {
"type": "integer",
"minimum": 0,
"description": "Display order position (0-indexed)"
},
"stemType": {
"type": "string",
"maxLength": 100,
"description": "Type/category of the stem",
"knownValues": [
"drums",
"bass",
"vocals",
"synth",
"guitar",
"keys",
"pad",
"lead",
"fx",
"other"
]
},
"audioHash": {
"type": "string",
"maxLength": 200,
"description": "SHA-256 hash of the stem audio content"
},
"bpmCentis": {
"type": "integer",
"maximum": 99900,
"minimum": 2000,
"description": "Centi-BPM (BPM × 100), integer — the Lexicon model has no float type; decode as `bpmCentis / 100` on read. Mirrors `fm.freemix.release.track`."
},
"createdAt": {
"type": "string",
"format": "datetime",
"maxLength": 100,
"description": "Record creation timestamp"
},
"detachedAt": {
"type": "string",
"format": "datetime",
"maxLength": 100,
"description": "FM-504 tombstone: when the parent link was severed"
},
"musicalKey": {
"type": "string",
"maxLength": 10,
"description": "Musical key (e.g., 'Am', 'F#m', 'Bb'). Deliberately named `musicalKey`, NOT the track lexicon's `key`: `key` is dangerously overloaded in a data layer (record keys, rkeys, map keys), so `musicalKey` is collision-proof and self-documenting. Intentional divergence."
},
"audioFormat": {
"type": "string",
"maxLength": 100,
"description": "Audio file format",
"knownValues": [
"wav",
"flac",
"mp3"
]
},
"coverArtUrl": {
"type": "string",
"format": "uri",
"maxLength": 3000,
"description": "URL to cover art image"
},
"description": {
"type": "string",
"maxLength": 5000,
"description": "Stem description"
},
"parentGroup": {
"type": "string",
"format": "at-uri",
"maxLength": 3000,
"description": "AT URI of the parent fm.freemix.group.stems this stem belongs to (optional). FM-549 s38: stems may carry an optional parentTrack AND an optional parentGroup back-ref — the only upward refs in the model (containers otherwise point down at members)."
},
"parentTrack": {
"type": "string",
"format": "at-uri",
"maxLength": 3000,
"description": "AT URI of the parent track this stem belongs to (optional for standalone stems)"
},
"aiDeclaration": {
"type": "object",
"required": [
"category"
],
"properties": {
"tools": {
"type": "array",
"items": {
"type": "string",
"maxLength": 100
},
"maxLength": 10,
"description": "AI tools used"
},
"category": {
"type": "string",
"maxLength": 100,
"description": "Level of AI involvement",
"knownValues": [
"none",
"assisted",
"augmented",
"generated"
]
},
"description": {
"type": "string",
"maxLength": 1000,
"description": "Creator's description of how AI was used"
}
},
"description": "Declaration of AI involvement in creation"
},
"audioSizeBytes": {
"type": "integer",
"description": "Size of the audio file in bytes"
},
"parentGroupCid": {
"type": "string",
"format": "cid",
"maxLength": 200,
"description": "CID of the parent stems-group record (pins to exact version)."
},
"parentTrackCid": {
"type": "string",
"format": "cid",
"maxLength": 200,
"description": "CID of the parent track record (pins to exact version)"
},
"audioDurationMs": {
"type": "integer",
"description": "Duration of the stem in milliseconds"
},
"previouslyAttachedToCid": {
"type": "string",
"format": "cid",
"maxLength": 200,
"description": "FM-504 tombstone: CID of the former parent track record at detach time"
},
"previouslyAttachedToUri": {
"type": "string",
"format": "at-uri",
"maxLength": 3000,
"description": "FM-504 tombstone: AT URI of the former parent track, set when this stem was detached (parent deleted, keep-stems path). Preserves remix-tree placement + royalty-lineage reconstructability"
}
}
},
"description": "A stem (isolated track component). Top-level leaf (FM-549 s38: pulled out from under release.* ; release.stem -> stem). May optionally reference a parent track and/or a parent stems-group."
}