# 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.