Metadata Types

Transform supports numerous types of sample based metadata. Each metadata type defines specific sample information and where that information is stored in the container. There are two categories of metadata:

• metadata embedded in the media sample data (e.g. VBI, MPEG-2 user data, AVC SEI messages, etc.)
• metadata stored in a seperate track or elementary stream (e.g. MXF 436M ancillary data, MOV captions, SCTE-35 splice information)

By default all available metadata in both categories is read from the input container and added to the appropriate samples. Similarly all sample metadata is written to the output container if supported by the container and stream formats.

Metadata Ordering

In many compressed formats (e.g. AVC and HEVC) video samples may be temporally reordered i.e. the samples are stored in a different order than they are displayed. Metadata elements are added to the video samples with a specific order based on the metadata type:

• storage order metadata remains with the associated sample (i.e. the metadata is reordered for storage)
• display order metadata is not reordered (i.e. the metadata is moved to different samples for storage).

The metadata elements are reordered when the stream is encoded, decoded or merged with a stream in a different order.

Metadata Tree

Each media sample contains a collection of root metadata elements. A metadata element may itself contain other elements forming a tree as illustrated below. The leaf elements of this tree contain the sample information.

The example above illustrates an MPEG-2 transport stream containing an h.264 video elementary stream. Each video sample contains several root metadata elements:

• ATSC A/72 Caption Data a72c stored in an AVC Supplemental Enhancement (SEI) message (in storage order).
• SMPTE RDD11 Ancillary Data rd11 stored in a seperate packetized elementary (PES) stream (in display order).
• SCTE-35 Splice Information sc35 also stored in a seperate PES stream (in display order).

The leaf elements representing the sample information include:

• CEA-708 Closed Captions c708.
• CEA-608 Closed Captions c608.
• ATSC A/65 Caption Service Descriptor csd .
• SCTE-35 Slice Information sc35 (also a root element).

Note that the metadata tree can contain multiple instances of the same metadata type (c708 in this case).

Metadata Operators

Use the Metadata Operators to attach or detach a leaf element to (or from) a specific root element.

Supported Types