Recordings

Recordings are a powerful debug tool. It allows full capturing of the data and then later streaming it back so that application can simulate the exact same state they were in.

OpenNI supports recordings of the Production Nodes graph - both the entire configuration of each node, and a capturing of all the data that streamed from the node.

OpenNI has a framework for recording data and for playing it back (using Mock Nodes). It also comes with the nimRecorder module, which defines a new file format - .ONI - and implements a Recorder node and a Player node for this format.

Making a Recording

To record, an application should create a Recorder node, and set its destination (the file name to write to). Then, it needs to add to it every node it wants to record. When adding a node to the recorder, the recorder reads its configuration and records it. It also registers to every possible event of the node, so that when any configuration change takes place, it will also be recorded.

Once all required nodes were added, the application can then read data from the nodes and record it. Recording of data can be acheived either by explicitly calling the xnRecord() function, or by using one of the UpdateAll functions (see Making Data Available using the WaitXUpdateAll() Methods).

Applications that init OpenNI using an XML file can easily record their session without any change to the code. They simply need to create an additional node in the XML file for the recorder, add nodes to it, and when the application calls one of the UpdateAll functions, recording will take place.

Playing Back a Recording

To play a file recording, use the xnContextOpenFileRecording() function (xn::Context::OpenFileRecording()). OpenNI will open the file, create a mock node for each node in the file, and fill it with the recorded configuration.

Next, an application may take the nodes it needs by calling xnFindExistingNodeByType(), and use them normally. Note that nodes created by the player are locked for changes, as the configuration must remain the recorded configuration.

Applications that init OpenNI using an XML file can easily replace their input so instead of reading from a real-time device they would read from a recording by simply replacing the nodes in the xml with a Recording element (see Recordings).

Limitations

In current version some limitations apply to recordings:

• Not all node types are supported for recording. Supported types are:
  • Device
  • Depth
  • Image
  • IR
  • Audio

• Opening more than one recording can cause undetermined behavior and is not supported.

• Opening a recording and a real-time sensor can cause undetermined behavior is not supported.