# 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 ``, ``, and ``. Connection metadata frames are sent automatically to each existing and new connection after being registerd with the NDI SDK and are received as normal metadata frames. ## Audio Frame Metadata Audio frame metadata is used for communicating information that is specific to a particular audio frame. There are currently no specific metadata elements defined for audio metadata frames. ## Video Frame Metadata Video frame metadata is used for communicating information that is specific to a particular video frame. Example metadata elements that should be passed as video frame metadata include ``, ``, and ``. {% hint style="info" %} 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. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter: ``` GET https://docs.ndi.video/all/developing-with-ndi/ndi-metadata/metadata-sources.md?ask= ``` The question should be specific, self-contained, and written in natural language. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.