vcap_reader.h File Reference

Indexed playback of MCAP-format bag files (.vcap / .vcapx). More...

#include <future>
#include <memory>
#include <string>
#include <vector>
#include "./bag_reader.h"

Include dependency graph for vcap_reader.h:

Go to the source code of this file.

Classes
class	vlink::VCAPReader
	Concrete MCAP-format BagReader implementation with index-driven seek. More...

Namespaces
	vlink

Detailed Description

Indexed playback of MCAP-format bag files (.vcap / .vcapx).

VCAPReader concretises BagReader for the MCAP container used by Foxglove Studio and other MCAP-compatible visualisers. Splits captured into .vcapx manifests are followed transparently; reindex() and fix() resolve to false because MCAP itself owns the footer index and does not support in-place repair through this implementation.

VCAP file format

+---------------------------------------------------------------+
| MCAP magic + header                                           |
+---------------------------------------------------------------+
| schemas (encoded SchemaData)                                  |  <- detect_schema() enumerates these
+---------------------------------------------------------------+
| channels (topic url -> schema)                                |
+---------------------------------------------------------------+
| message chunks (optionally Zstd compressed)                   |  <- streamed during play()
+---------------------------------------------------------------+
| attachments / metadata                                        |
+---------------------------------------------------------------+
| summary section (message + chunk + channel + schema indexes)  |  <- used for fast seek / jump
+---------------------------------------------------------------+
| footer (offset of summary section)                            |
+---------------------------------------------------------------+

Reader states

+---------+   play()        +---------+   pause()       +---------+
| stopped | --------------> | playing | --------------> | paused  |
+---------+                 +---------+                 +---------+
     ^                         |  ^                          |
     |                         |  | resume() / pause_to_next()|
     +--- stop() or EOF -------+  +--------------------------+
                              |
                              |  jump(time, rate, times)
                              v
                          +---------+
                          | seeking |  briefly during random access
                          +---------+

Example

auto reader = vlink::BagReader::create("/data/recording.vcap");
 
reader->register_output_callback([](const vlink::Frame& frame) {
  VLOG_I(frame.timestamp, " ", frame.url, " bytes=", frame.data.size());
});
 
reader->async_run();
reader->play({});

See also

BagReader, VDBReader