Proposed New Metadata Messages

<vancData> Element (CEA-708 & SCTE-104)

Initial Implementation: ToolsOnAir

Location: Video Frame Metadata

Legacy close captioning data and SCTE triggers are passed as NDI metadata by encoding the corresponding SDI vertical ancillary data packets directly as XML. Note that this method should not be used as a general solution for transitting SDI Ancillary data via NDI, but is used in this case because workflows using these protocols are very SDI centric and this method is supported by existing equipment and workflows.

This mechanism should NOT be used to tunnel arbitrary SDI ancillary data which can readily be represented by XML.

<vancData version="1.0">
  <vancPacket did="97" sdid="1" line="9">lmlZT38BWHL0/ICA...3QBWEY=</vancPacket>
  <vancPacket did="65" sdid="7" line="10">CP//AB4AAQEAAgAAAQEBAA4BAAAAAwAAAAAAAAAAAA==</vancPacket>
</vancData>

<vancData> Attributes

Attribute	Description
version	The <vancData> element must have a version attribute. The version attribute supported by this standard is "1.0"

<vancData> Children

Child	Description
vancPacket	This element contains the details for one ancillary data packet. Any number of vancPacket elements may be contained within one vancData element

vancPacket Element

The vancPacket element provides details for one SMPTE ST-291 ancillary data packet. The various ST-291 elements map to the vancPacket element as follows:

• ADF: Ancillary Data Flag: Not transmitted

• DID: Data ID: Sent as an attribute

• SDID: Secondary DID: Sent as an attribute

• DC: Data Count: Not transmitted

• UDW: User Data Words: Sent as text content, 8-bit, base64 encoded

• CS: Checksum: Not transmitted

Note that the user data word content of the ancillary data packet is sent as base64 encoded 8-bit data. Bits 8 (parity) and 9 (NOT bit 8) are not transmitted.

DID and SDID values and ancillary data content are per SMPTE standards ST-334 (CEA-708) and ST-2010 (SCTE-104).

The following ancillary data packet types are currently supported:

• CEA-708 close caption: did="97" sdid="1"

• SCTE-104 trigger: did="65" sdid="7"

<vancPacket did="xs:int" sdid="xs:int" line="xs:int">xs:base64Binary</vancPacket>

vancPacket Attributes

Attribute	Description
did	The ancillary packet DID (Data Identifier)
sdid	The ancillary packet SDID (Secondary Data Identifier)
line	The line number the ancillary data packet was received on

Midi <ndi_metadata type="midi"> Element

Initial Implementation: Lamamix

Location: Metadata Frame

Initial NDI Version: 6.1

<ndi_metadata type="midi">
  <data>903C403D20</data>
</ndi_metadata>

Midi <ndi_metadata type="midi"> Children

Child	Description
data	Hexidecimal representation of a midi message. Data is read left to right (eg: 0x90 is the first byte transmitted and 0x20 is the last byte to be trasmitted)

DMX <ndi_metadata type="dmx"> Element

Initial Implementation: Salrayworks

Location: Metadata Frame

Initial NDI Version: 6.1

Some early versions of DMX used the tag <SALRAY_DMX> instead of <ndi_metadata type="dmx">. Devices receiving DMX via NDI Metadata should look for both element names. Devices sending DMX via NDI metadata should use the <ndi_metadata type="dmx"> element with NDI SDK version 6.1 or newer.

<!-- Devices receiving DMX should also look for the <SALRAY_DMX> Element -->
<ndi_metadata type="dmx">
  <Universe id="1">
    <Stream>
      <Address>"1"</Address>
      <Data>01FF0304050607</Data>
    </Stream>
    <Stream>
      <Address>"8"</Address>
      <Data>1A10A0023</Data>
    </Stream>
  </Universe>
  <Universe id="2">
    <Stream>
      <Address>2</Address>
      <Data>02FF004567</Data>
    </Stream>
  </Universe>
  <Universe id="3">
    <!-- No streams for this universe -->
  </Universe>
</ndi_metadata>

DMX <ndi_metadata type="dmx"> Children

Child	Description
Universe	DMX transmit channel. Multiple universe elements are allowed

Universe Attributes

Attribute	Description
id	DMX transmit channel: 1 (first channel) to the capacity of the DMX controller

Universe Children

Child	Description
Stream	Represents DMX data. Multiple stream elements are allowed

Stream Children

Child	Description
Address	Starting DMX channel: 1 to 512
Data	Hexidecimal representation of DMX data. Data is read left to right (eg: 0x01 is the first byte transmitted for universe 1, address 1

Timed Text Captions

• Initial Implementation: Various standards bodies

• Location: Metadata Frame

Modern captioning solutions are migrating to a variety of XML based timed text formats such as:

• TTML1

• SDP-US

• IMSC1

• SMPTE-TT

• EBU-TT

• CFF-TT

As these formats are natively XML they can be easily incorporated into an NDI stream as metadata. As a transport protocol, NDI does not natively prefer any one of these standards over the others. The properly formed XML conforming to one (or more) of these standards should simply be sent as an NDI metadata frame, optionally as the child of an <ndi_metadata_group> element if for some reason more than one element needs to be sent in the same metadata frame.

W3C has a good overview of the various timed text caption standards including links to many of the specifications: https://www.w3.org/AudioVideo/TT/docs/TTML-Profiles.html

As a general rule, it is suggested that applications sending timed-text captions use the minimum set of features necessary for full operation. Receivers should be able to process any Well Formed XML, ignoring any elements or attributes they do not currenntly implement.

If you are interested in supporting any of the timed-text captioning solutions in real-world workflows, the NDI team would be happy to coordinate with you to help insure consistency and interoperability across the NDI ecosystem.