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crosstyan d0f3dc5cf1 docs(mcap): split legacy single-camera layout reference

Move the legacy /camera/* contract into its own reference page so the main MCAP layout doc can stay focused on current bundled and copy-layout behavior.

Document the compatibility model explicitly: legacy single-camera is operationally equivalent to one-camera copy when the effective camera label is treated as the literal `camera`.

Update the mcap_rgbd_example helper and recipe docs to accept legacy /camera/* inputs under that compatibility rule instead of rejecting them.

2026-03-24 18:56:52 +08:00

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Legacy Single-Camera MCAP Layout

This page is the reference for the older /camera/* MCAP wire shape.

It is still used by some generic sink/tester paths in the repository, but it is no longer the default shape written by zed_svo_to_mcap for a single .svo or .svo2 input.

Compatibility With Copy Layout

In practice, this layout is very close to the one-camera copy shape:

legacy single-camera uses /camera/video, /camera/depth, and related /camera/* topics
one-camera copy uses /{label}/video, /{label}/depth, and related /{label}/* topics

So the compatibility mental model is:

treat the camera label as the literal camera
replace /{label}/... with /camera/...
there is still no /bundle
timestamps remain per-camera sample timestamps

That is why legacy single-camera is conceptually compatible with copy, even though the topic paths are not namespaced the same way.

Topics

Topic	Schema / Encoding	Notes
`/camera/video`	`foxglove.CompressedVideo`	H.264 or H.265 Annex B access units
`/camera/depth`	`cvmmap_streamer.DepthMap`	RVL-compressed depth payload
`/camera/calibration`	`foxglove.CameraCalibration`	Video intrinsics
`/camera/depth_calibration`	`foxglove.CameraCalibration`	Written only when depth resolution differs from video
`/camera/pose`	`foxglove.PoseInFrame`	Optional; only when pose export is enabled and tracking is valid
`/camera/body`	raw `cvmmap.body_tracking.v1`	Optional raw body-tracking packets; see mcap_body_tracking.md

Timestamp Semantics

Legacy single-camera export preserves the original per-frame source timestamp on video, depth, and pose messages.

Like copy, there is no separate bundle time:

/camera/video, /camera/depth, and /camera/pose use the original camera sample timestamp
calibration and depth-calibration messages use the timestamp of the first emitted sample

Corruption Behavior

Like copy, this layout has no manifest or placeholder contract:

unreadable tail frames are treated as end-of-stream
mid-stream corruption is skipped until a readable frame is found
the topic stream simply resumes at the recovered readable frame

Validation Expectations

The current validation contract is:

/camera/video must exist and contain at least one message
/camera/depth must exist and contain at least one message
/camera/calibration must exist exactly once
/camera/video and /camera/depth message counts must match
/camera/depth_calibration may appear zero or one time
/camera/pose is optional, but it may not outnumber /camera/video

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