cvmmap-streamer/docs/mcap_body_tracking.md

MCAP ZED Body Tracking Contract

cvmmap-streamer records native cv-mmap ZED body-tracking packets into MCAP as a raw binary channel.

Channel

• default topic: /camera/body
• messageEncoding: cvmmap.body_tracking.v1
• schema: none (schemaId = 0)
• channel metadata:
  • packet_layout = cvmmap_body_tracking_v1
  • payload_format = raw
  • source_transport = cv-mmap-body-pub

The channel is created lazily on the first valid body packet, so non-body inputs do not produce an empty /camera/body channel.

Payload

Each MCAP message payload is byte-for-byte identical to the cv-mmap ZED body PUB packet:

• 64-byte body_tracking_message_header_t
• followed by body_count packed body_tracking_body_t records

The intended parser contract is the existing cv-mmap body-tracking v1 layout:

• cvmmap::parse_body_tracking_message(...)
• cv-mmap/docs/cvmmap_body_tracking_v1.ksy

This recording path does not remap joints, filter fields, or convert the packet into protobuf/JSON.

Timing And Alignment

• logTime and publishTime use header.timestamp_ns
• if header.timestamp_ns == 0, they fall back to header.sdk_timestamp_ns
• cross-topic alignment should use body frame_count and timestamps, not MCAP file order

Configuration

MCAP body capture follows the normal MCAP recording switch:

• enable MCAP with --mcap or record.mcap.enabled = true
• override the body topic with --mcap-body-topic or record.mcap.body_topic

There is no separate body-enable flag. If the input never emits body packets, no body channel is written.