Metadata Sources

Metadata Frame (NDIlib_metadata_frame_t)

This is the "normal" metadata channel for sending messages between NDI senders and receivers. This channel is bidirectional and is used for generic communications which do not have a specific association with a particular audio or video frame.

Connection Metadata

Connection metadata is a special class of metadata frames that can be registered with the NDI SDK for both the sender and receiver. Upon establishing a new NDI connection, the connection metadata is sent from sender to receiver and from receiver to sender. There are several standard connection metadata elements including <ndi_product>, <ndi_capabilities>, and <ndi_format>.

Connection metadata frames are automatically sent to each existing and new connection after being registered with the NDI SDK and are received as normal metadata frames.

Audio Frame Metadata

Audio frame metadata communicates information specific to a particular audio frame. Currently, no specific metadata elements are defined for audio metadata frames.

Video Frame Metadata

Video frame metadata is used to communicate information specific to a particular video frame. Example metadata elements that should be passed as video frame metadata include <ndi_tracking_info>, <ndi_color_info>, and <vancData>.

Applications using video frame metadata must account for the possibility that individual video frames can be dropped or duplicated, potentially causing missing or replicated metadata. This behavior is typically caused by the use of an NDI frame synchronizer instance, which occasionally drops or duplicates video frames to match frame rates between the NDI sender and receiver.

In addition, prior to NDI 5.x, the preview video stream was limited to 30 fps, so preview streams created from full streams with greater than 30 fps would drop video frames to meet the 30 fps maximum. Starting with NDI 5.0, preview streams are now sent using the same frame rate as the full stream. Users of the ASDK need to ensure that any required video frame metadata is attached to both the full and preview frames submitted to the ASDK.