Class VideoTransmissionOperator

• Defined in File video_transmission_operator.hpp

Base Type

• public holoscan::Operator (Class Operator)

class VideoTransmissionOperator : public holoscan::Operator

Base class for video transmission (output) operators.

Declares a standard signal input carrying holoscan::gxf::Entity, aligned with acquisition and passthrough operators for multi-input / single-output compositions.

Subclasses must implement compute(). Override query_capabilities() for hardware-specific enumeration without starting output.

==Dynamic Port Allocation==

The number of input streams is set via the num_streams constructor parameter (default 1). Because make_operator calls the constructor before setup(), the stream count is available at port-registration time — only the requested number of ports are created. All registered ports get proper backpressure scheduling (no dormant ports with ConditionType::kNone).

==num_streams vs channel_indices==

num_streams controls port allocation (how many input ports setup() registers). channel_indices is a capability-reporting parameter that describes which hardware channels appear in the VideoTransmitCapabilities snapshot. These are intentionally independent.

==Named Inputs==

• signal : stream 0 (std::shared_ptr<holoscan::gxf::Entity>), always registered.

• signal_1 … signal_N : additional streams, registered only when num_streams > 1.

==Parameters==

Same common channel / URI / format parameters as VideoAcquisitionOperator.

Public Functions

HOLOSCAN_OPERATOR_FORWARD_ARGS (VideoTransmissionOperator) VideoTransmissionOperator()=default

explicit VideoTransmissionOperator(uint32_t num_streams)

Construct with a specific number of input streams.

Parameters

num_streams – Number of input ports to register (1 .. kVideoIoMaxStreams). Clamped to [1, kVideoIoMaxStreams].

HOLOSCAN_OPERATOR_FORWARD_TEMPLATE () explicit VideoTransmissionOperator(uint32_t num_streams

inline ArgT ArgsT std::min (num_streams, video_io::kVideoIoMaxStreams)))

virtual void setup(OperatorSpec &spec) override

Define the operator specification.

Parameters

spec – The reference to the operator specification.

virtual void initialize() override

Initialize the operator.

This function is called when the fragment is initialized by Executor::initialize_fragment().

virtual video_io::VideoTransmitCapabilities query_transmit_capabilities() const

video_io::VideoDeviceCapabilities query_capabilities() const

inline uint64_t dropped_frame_count() const

inline uint64_t transmitted_frame_count() const

bool is_transmit_stream_enabled(uint32_t stream_index) const

Returns

true if stream_index < num_streams().

inline uint32_t num_streams() const

Returns

Number of input streams registered in setup().

Public Members

ArgT &&arg

ArgT ArgsT && args

Protected Functions

inline void note_dropped_frame()

inline void note_transmitted_frame()

std::shared_ptr<holoscan::gxf::Entity> receive_transmit_stream(InputContext &op_input, uint32_t stream_index)

Receive an entity from the given transmit stream port.

Symmetric counterpart to VideoAcquisitionOperator::emit_capture_stream(). Throws std::out_of_range if stream_index >= num_streams().

Returns

The received entity, or an empty shared_ptr if nothing was available.

virtual video_io::VideoTransmitCapabilities build_transmit_capabilities_from_parameters() const

virtual void compute(InputContext &op_input, OutputContext &op_output, ExecutionContext &context) override = 0

Implement the compute method.

This method is called by the runtime multiple times. The runtime calls this method until the operator is stopped.

Parameters

• op_input – The input context of the operator.

• op_output – The output context of the operator.

• context – The execution context of the operator.

Protected Attributes

Parameter<std::string> backend_id_

Parameter<uint32_t> channel_index_

Parameter<std::vector<uint32_t>> channel_indices_

Parameter<std::string> uri_

Parameter<uint32_t> width_

Parameter<uint32_t> height_

Parameter<float> frame_rate_

Parameter<std::string> pixel_format_

Parameter<std::string> color_space_

Parameter<std::string> transport_

Parameter<YAML::Node> vendor_extensions_

Protected Static Functions

static std::string transmit_input_port_name(uint32_t stream_index)

Return the input port name for a given stream index.

Index 0 returns "signal" (not "signal_0") for backward compatibility with single-stream operators. Indices 1+ return "signal_1", "signal_2", etc. Validates against kVideoIoMaxStreams (global max), not the per-instance num_streams().