Experimental:OAK Select CHOP


The OAK Select CHOP is like a Script CHOP combined with a Select CHOP, and any of the other hardware-specific CHOPs. The basic operation involves providing an OAK Device CHOP and a stream name. In the simplest case, the stream's data will show up as well-named channels. For example, ImgDetections messages indicating the 2D coordinates and labels of detected objects will show up as CHOP channels without any manual coding. In more complex cases such as hand landmark tracking, the stream may be of NNData or Buffer type, requiring the user to implement a callback and parse the data.


Parameters - OAK Page

Active active -

OAK Device CHOP chop -

Stream stream -

Queue Size queuesize -

Max Items maxitems -

Output Format outputformat - -

  • Items As Separate Channels itemsaschannels -
  • Items As Separate Samples itemsassamples -

Use First Sample Only firstsample - Only use the most recently received message with the OAK Select CHOP. For example, an IMU stream is sending very high-frame rate data, toggling this parameter will only show the latest sample.

Sample Rate rate -

Callbacks DAT callbacks -

Setup Parameters setuppars -

Parameters - Common Page

Time Slice timeslice - Turning this on forces the channels to be "Time Sliced". A Time Slice is the time between the last cook frame and the current cook frame.

Scope scope - To determine which channels get affected, some CHOPs use a Scope string on the Common page.

Sample Rate Match srselect - - Handle cases where multiple input CHOPs' sample rates are different. When Resampling occurs, the curves are interpolated according to the Interpolation Method Option, or "Linear" if the Interpolate Options are not available.

  • Resample At First Input's Rate first - Use rate of first input to resample others.
  • Resample At Maximum Rate max - Resample to the highest sample rate.
  • Resample At Minimum Rate min - Resample to the lowest sample rate.
  • Error If Rates Differ err - Doesn't accept conflicting sample rates.

Export Method exportmethod - - This will determine how to connect the CHOP channel to the parameter. Refer to the Export article for more information.

  • DAT Table by Index datindex - Uses the docked DAT table and references the channel via the index of the channel in the CHOP.
  • DAT Table by Name datname - Uses the docked DAT table and references the channel via the name of the channel in the CHOP.
  • Channel Name is Path:Parameter autoname - The channel is the full destination of where to export to, such has geo1/transform1:tx.

Export Root autoexportroot - This path points to the root node where all of the paths that exporting by Channel Name is Path:Parameter are relative to.

Export Table exporttable - The DAT used to hold the export information when using the DAT Table Export Methods (See above).

Operator Inputs

Info CHOP Channels

Extra Information for the oakselect CHOP can be accessed via an Info CHOP.

Common CHOP Info Channels

  • start - Start of the CHOP interval in samples.
  • length - Number of samples in the CHOP.
  • sample_rate - The samplerate of the channels in frames per second.
  • num_channels - Number of channels in the CHOP.
  • time_slice - 1 if CHOP is Time Slice enabled, 0 otherwise.
  • export_sernum - A count of how often the export connections have been updated.

Common Operator Info Channels

  • total_cooks - Number of times the operator has cooked since the process started.
  • cook_time - Duration of the last cook in milliseconds.
  • cook_frame - Frame number when this operator was last cooked relative to the component timeline.
  • cook_abs_frame - Frame number when this operator was last cooked relative to the absolute time.
  • cook_start_time - Time in milliseconds at which the operator started cooking in the frame it was cooked.
  • cook_end_time - Time in milliseconds at which the operator finished cooking in the frame it was cooked.
  • cooked_this_frame - 1 if operator was cooked this frame.
  • warnings - Number of warnings in this operator if any.
  • errors - Number of errors in this operator if any.

TouchDesigner Build:

Script CHOP Functionality

The OAK Select CHOP mimics the Script CHOP in several ways. There's a callback for onSetupParameters, where custom parameters can be added. Also, in the other callbacks such as onReceiveNNData, onReceiveBuffer, and onReceiveSystemInformation it's possible to append channels and write data.

def onReceiveNNData(oakSelectOp, oakNnData: dai.NNData):
    oakSelectOp.isTimeSlice = False
    oakSelectOp.numSamples = 1
    oakSelectOp['foo'][0] = 42    

Queue Size

The Queue Size parameter helps TouchDesigner avoid holding onto too many messages while also re-using memory for a minimum number of messages. For example, picking 2 is a good choice because TouchDesigner can show 1 message to the user while 1 remaining message can asynchronously be written to with new data. However, if the stream is meant to be high frame-rate, such as IMU data, then the queue size should be at least double the number of messages you expect to receive in a single TouchDesigner frame.

Max Items

Some messages can be described as items. For example, ImgDetections can be grouped into item0's channels, item1's channels, item2's channels and so on. For these kinds of streams, it can be helpful to have a constant number of channels in the OAK Select CHOP, regardless of whether an item exists in the most recent message.

Output Format

When using a stream that involves items, it can be convenient to make the OAK Select shuffle its channels into new samples. Each sample would correspond to a unique item, and the number of samples would correspond to the Max Items parameter.

Use First Sample Only

Like the Shuffle CHOP, the Use First Sample Only parameter makes it easy to only use the most recently received message with the OAK Select CHOP. For example, an IMU stream might be sending very high-frame rate data, and toggling this parameter on would be like using a Trim CHOP in "Absolute" value mode to only show the latest sample.


When an OAK Select CHOP is connected to an Info CHOP, in addition to the regular cook-related channels, there will be a few OAK-specific ones:

  • sequence_num: (see "sequenceNum" in the depthai documentation)
  • messages_received: the total number of messages received with stream name set on the OAK Select CHOP
  • fps: The effective frames-per-second of this stream, i.e., how quickly TouchDesigner is receiving messages. This is not the target FPS of the stream.

See Also