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feat(protocol): MMCP 1.2 — motion and video references as prompts (0.9.0) - #9
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- MotionReferenceSegment: joint_names, rotations (T x J x 4, local, as
pose_keyframe), root_positions (T x 3), fps, fidelity in [0, 0.2]
(default 0), duration_frames optional (default: the reference length);
T >= 2 and consistent lengths are schema-checked, quaternions taken as sent
- a reference stands alone: a second one, another segment, or options.loop
is 400 invalid_request (new code); its joints must be on the skeleton
- limits.max_reference_frames (optional) caps the reference and
duration_frames (invalid_options); omitted from /capabilities when unset;
models without "motion_reference" in supported_segments still get
unsupported_segment
- the backbone gets the segment as parsed (req.motion_reference,
.output_frames); the SDK sets no guidance default, so a backbone picks its
own per segment type
- MMCP_motion.samples[b].reference = {"fidelity": f}, read back by the
client parser
- PROTOCOL_VERSION 1.2; docs (segments, capabilities, request, response,
errors, versioning, backbone) and a CHANGELOG under Unreleased
Package version set at release.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
- MotionReferenceSegment.skeleton (optional, the request Skeleton schema): the clip's own rig, so a reference can come from any rig; when set, joint_names / rotations / root_positions refer to it and the server retargets the clip from it; output stays on the request skeleton - unknown_joint is checked against the segment skeleton when given; a non-canonical one needs supports_retargeting (retargeting_unsupported) - duration_frames may differ from the reference length; fidelity > 0 needs them equal (400 invalid_request) - docs (segments, request, backbone, errors) and CHANGELOG Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
- ModelSpec.supports_motion_reference_mixed (default false): on a model
that sets it a request may carry any number of motion_reference segments,
in any order, mixed with text / unconditioned ones, each covering its own
stretch of the take and stitched with the same transitions
- with more than one segment each reference needs duration_frames (as a
text segment) and fidelity 0 -> 400 invalid_request, details.segment
names it; a pose segment never goes with a reference; options.loop with
any reference is still invalid_request
- without the flag a reference still stands alone, so existing backbones
are unchanged
- every reference is checked on its own (its skeleton, joints, fidelity
length rule, max_reference_frames)
- MotionReferenceSegment.seed: per-segment seed, as TextSegment.seed
- GenerateRequest.motion_references; samples[b].reference stays
{"fidelity": f} (0 in a mixed request)
- docs (segments, request example with two clips, capabilities, backbone,
errors, versioning) and CHANGELOG; tests 141 -> 155
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…a motion A reference is validated with exactly the text segment's rules: duration_frames required, per-segment seed, mixing with any segment in any order, loop on a supports_loop model, constraints, guidance and batches as for text. Only its payload has checks of its own (shapes, joints on its skeleton, the clip against limits.max_reference_frames, which no longer caps the output). Removed: the lone-reference rules, fidelity (deprecated, accepted as 0 only and not passed on), the loop and pose refusals, and the response's samples[].reference metadata. supports_motion_reference_mixed is implied and advertised true for every model that lists motion_reference. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
- VideoReferenceSegment (type "video_reference"): a text segment whose
prompt is a video. video = {"url": https} or {"data": base64,
"media_type": video/mp4 | video/quicktime | video/webm}; optional
start_s / end_s trim (0 <= start < end), person, fps hint, seed.
Validated with the text segment's rules, as motion_reference is; the SDK
checks the payload and never decodes the video
- limits.max_video_bytes (inline data's decoded size -> 413
payload_too_large) and limits.max_video_seconds (a trimmed video -> 400
invalid_options), details.segment naming it; left out of /capabilities
when unset. A URL's size and an untrimmed length are the server's
- models opt in via supported_segments; the unsupported_segment gate still
refuses it elsewhere
- GenerateRequest.video_reference(s), VideoSource.decoded() / .num_bytes
- motionmcp.client.video_source(): a file (base64) or https URL as the
video object, stdlib only
- fix: a schema validator's own error is a 422 envelope, not a 500 from an
unserialisable ctx
- reference tests skip without the [server] extras (client-only job)
- docs (segments, generate-request, capabilities, errors, backbone,
client, versioning, roadmap); CHANGELOG is the 0.9.0 section
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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📝 WalkthroughWalkthroughThe pull request adds MMCP 1.2 motion- and video-reference segments, schema and server validation, capability and limit reporting, and a client helper for video sources. It also updates protocol documentation, release notes, and tests. ChangesMMCP 1.2 reference segments
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Feature · Severity of issue fixed: Low Sequence Diagram(s)sequenceDiagram
participant GenerateRequest
participant Server
participant ModelSpec
participant Backbone
GenerateRequest->>Server: Submit request with reference segments
Server->>ModelSpec: Check supported segments and configured limits
Server->>Backbone: Forward validated reference segments
Backbone-->>Server: Return generated result
Merge Risk: 🔵 Low · up to The change is mergeable with a bounded validation gap: malformed HTTPS URLs pass the client helper but are safely rejected by the server. Aligning hostname validation would report these errors earlier. Security Architecture ReviewSecurity architecture risk: 🟡 Moderate · up to Inline video is fully base64-decoded before its size or feature support is checked. Rejected requests can therefore consume additional memory and processing time. Practical exposure depends on request-admission limits; protections for remote-video fetching remain unestablished. Retained concerns
Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 22.86% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 105 functions across 12 files. (11 skipped: 11 unsupported.)
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Inline comments:
Review comments at @src/motionmcp/client/video.py:
- Around line 41-43: Update video_source to use the same URL parsing and
scheme/hostname validation as VideoSource before returning the source, so
hostless HTTPS URLs are rejected by the helper. Add a test confirming
video_source rejects a hostless URL such as “https:///dance.mp4”.
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CHANGELOG.mddocs/docs/concepts/segments.mdxdocs/docs/protocol/roadmap.mdxdocs/docs/protocol/versioning.mdxdocs/docs/reference/capabilities.mdxdocs/docs/reference/errors.mdxdocs/docs/reference/generate-request.mdxdocs/docs/reference/response.mdxdocs/docs/sdk/backbone.mdxdocs/docs/sdk/client.mdxdocs/docs/sdk/errors.mdxsrc/motionmcp/__init__.pysrc/motionmcp/backbone.pysrc/motionmcp/client/__init__.pysrc/motionmcp/client/video.pysrc/motionmcp/errors.pysrc/motionmcp/protocol.pysrc/motionmcp/schemas.pysrc/motionmcp/server.pytests/test_client_video.pytests/test_motion_reference.pytests/test_smoke.pytests/test_video_reference.py
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A guide page (Guides > Building reference segments) for client authors: the clip's data model and conventions (Y-up metres, [x, y, z, w], local rotations from rest with identity rest_rotation, the root's world position), the skeleton and joint coverage, sampling (every frame, sign continuity, fps, max_reference_frames, the size budget), runnable numpy and Blender examples (the Blender one mirrors the Animatica add-on's Z-up to Y-up sampling), BVH and FBX pointers, building a video_reference (video_source, inline vs url and the size math, trim, person, fps), and a troubleshooting table. Linked from segments, generate-request, backbone and client. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
… in 1.2 - VideoReferenceSegment has no `person`: the server follows the most prominent person (largest, most visible); schema, tests, docs, guide and CHANGELOG updated, and the roadmap notes choosing among several people may come later (server reports the people it found, client picks one) - rest_rotation, as the reference server reads it: clients SHOULD send identity on every joint and express the rest orientation in the rotations (local rotations measured from rest, world-aligned frames); a server MAY ignore rest_rotation; fill_mode "rest" pins to identity. skeleton, constraints, guide and the 1.2 versioning entry say so - the guide's video size section: use a URL for anything over a few seconds Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
…tion - rest_rotation: 1.0 meanings stand (parent-local rest_translation / rest_rotation; fill_mode "rest" pins to rest_rotation). Clients SHOULD send identity; a server that can't honour a non-identity one MUST refuse it with 400 invalid_skeleton (skeleton, constraints, guide, versioning) - the SDK server enforces limits.max_request_bytes before parsing (Content-Length, and a streamed count for bodies without one) and each model's own cap after: 413 payload_too_large - video.data: its size worked out from the base64 length and padding, the alphabet checked by a regex, no decoded copy; decoded() decodes - 422 envelopes no longer echo the input (include_input=False) - skeleton topology errors (request or segment skeleton) are 400 invalid_skeleton, as documented - motion_reference numbers must be finite; fidelity is gone - a motion_reference must include its skeleton's root joint (400 invalid_request) - supports_motion_reference_mixed is exactly "motion_reference" in supported_segments - unsupported (or unknown) segment types are refused from the raw body, before their payload is parsed - video.url rule shared by schema, client and fetch: https (any case), a host, no user info, whitespace or control characters, a valid port - motionmcp.fetch_video_url: SSRF-safe fetch (public addresses only, pinned connection, every redirect checked, byte cap, deadline), and MUST guidance for backbones that fetch - video_source(): the server's URL rule, max_bytes before reading; docs on standard padded one-line base64 (base64 -w0) - max_reference_frames counts frames as sent (MUST, docs) - tests: NaN/Infinity over HTTP, envelope size, streamed and per-model body caps, base64 arithmetic, invalid_skeleton, root joint, the gate, /capabilities of an old backbone unchanged, fetch (faked network) Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
… JSON - fetch_video_url: one hard deadline over connect, TLS, headers and body (a timer shuts the socket; reads with read1); a dripping server is cut off at the timeout - is_public_address judges IPv6 forms that reach an IPv4 address by it: NAT64 64:ff9b::/96, IPv4-compatible ::/96, IPv4-mapped, 6to4, Teredo; NAT64 local-use 64:ff9b:1::/48 is never public - max_bytes optional (None -> DEFAULT_MAX_VIDEO_BYTES, 100 MiB), else a positive int; the refusal no longer lists the blocked addresses - a body nested too deeply to parse is a 422 envelope (RecursionError), single and batch - the protocol major is checked before the segment gate; the gate covers only types the SDK knows (unknown types stay 422) - batch items are held to their own model's max_request_bytes - base64 padding counted from the last two characters (no copy) - docs: fetch_video_url is synchronous (asyncio.to_thread), the default cap, the fetch example inside an async generate Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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MMCP 1.2 adds two new segment types. Each one is a prompt given as something other than words, and composes exactly like a
textsegment. This PR also finishes the 0.9.0 release notes:CHANGELOG.mdgets a single 0.9.0 section covering #7 (the trajectory now moves along its shape with the body), #8 (poll_joband phase-tagged client errors), and both reference types. Nothing is tagged or published.What 1.2 adds
motion_reference(MotionReferenceSegment): a clip (joint_names,rotationsT×J×4,root_positionsT×3,fps) goes where the prompt would. It can carry its ownskeleton, so the clip can come from any rig.limits.max_reference_framescaps the clip.video_reference(VideoReferenceSegment, new here): a video of a person goes where the prompt would.videomust be exactly one of:{"url": "https://…"}: the server fetches it.{"data": "<base64>", "media_type": "video/mp4" | "video/quicktime" | "video/webm"}start_s/end_strim (0 ≤ start_s < end_s),fpshint andseed. The server always follows the most prominent person (the largest, most visible one); choosing among several people is on the roadmap.extra="forbid"applies both on the segment and onvideo.limits.max_video_bytescaps the decoded size of inline data (413payload_too_large).limits.max_video_secondscapsend_s − (start_s or 0)(400invalid_options).details.segmentnames the segment in both cases.invalid_requestif it can't fetch or decode the video, or finds no person in it.video.decoded()andvideo.num_bytes.duration_framesrequired, per-segmentseed, mixes with any segment type in any order, andloop, constraints,num_samples, guidance and batches work as they do for text. The tests check this by sending each request both ways and comparing the results.invalid_requesterror code (400), for backbones.PROTOCOL_VERSION = "1.2".motionmcp.client.video_source(path | url=)(standard library only). It turns a file into base64 with the media type taken from the extension, or passes an https URL through.Examples
{ "protocol_version": "1.2", "model": "my-video-model", "skeleton": { "joints": [ … ] }, "segments": [ { "type": "text", "prompt": "a person walks forward", "duration_frames": 90, "seed": 7 }, { "type": "motion_reference", "duration_frames": 45, "joint_names": ["Hips", "…"], "rotations": [ … ], "root_positions": [ … ], "fps": 30 }, { "type": "video_reference", "duration_frames": 60, "video": { "url": "https://cdn.example.com/turn.mp4" }, "end_s": 2.5 } ] }{ "type": "video_reference", "duration_frames": 90, "video": { "data": "AAAAFGZ0eXBxdCAg…", "media_type": "video/quicktime" } }Implementations
video_referenceyet.motion_referenceon its own branch.Compatibility
supported_segments. A model that doesn't list a type still refuses it withunsupported_segment, and that gate covers each type separately. The optional limits are left out of/capabilitieswhen unset.Also in this PR
Docs: a new guide, Guides → Building reference segments, walks client authors through building both segment types. It covers the conventions, sampling a clip, runnable numpy and Blender examples, BVH and FBX pointers, the size budget, video sources and troubleshooting.
Clarified in 1.2: the 1.0 meanings stand:
rest_translationandrest_rotationare parent-local, andfill_mode: "rest"pins torest_rotation. Clients SHOULD send identityrest_rotationon every joint. A server that can't honour a non-identity one MUST refuse it with400 invalid_skeleton; Kimodo does.Review hardening:
max_request_bytesbefore parsing, and returns413.400 invalid_skeleton.fidelityfield is removed.invalid_request.supports_motion_reference_mixedis true exactly when a model listsmotion_reference.motionmcp.fetch_video_url: an SSRF-safe way for a backbone to fetch a video URL.max_reference_framescounts frames as sent, and a server MUST accept any clip within it.Fix: a request that failed one of the schema's own validators, for example mismatched
root_pathlengths, returned a 500. The validator'sValueErrorinerrors()[i]["ctx"]could not be serialised to JSON. It now returns the 422schema_validationenvelope.The reference tests now
importorskip("fastapi"), so theclient-onlyjob, which runs without the[server]extras, passes.Tests
client-onlyjob on 3.10 passes:pip install . pytest, with the smoke and batch tests ignored and the server tests skipped.npm run build) has no broken links or anchors.🤖 Generated with Claude Code
Summary by CodeRabbit
New Features
Bug Fixes
Documentation