Trace: • media
Table of Contents

The <media> Element

Definition and Usage

The <media> element defines a media object containing: perceptual media content; imperative code content; declarative code content; UTC content; or global variables for the application. The object type is defined by the type attribute or is inferred by the file extension used in the src attribute.

Four special types are defined:

  • The “application/x-ncl-NCL” (or “application/x-ginga-NCL”) type is applied to <media> elements with NCL code content (note thus that an NCL application can embedded another NCL application).
  • The “application/x-ncl-NCLua” (or “application/x-ginga-NCLua”) type is applied to <media> elements with Lua imperative code content.
  • The “application/x-ncl-settings” (or “application/x-ginga-settings”) is applied to a special <media> element (there may be only one in an NCL document, but it may be reused as child element of other <context> elements) whose properties are global variables (properties defined by the document author or reserved environment properties managed by the system) that may be manipulated by the NCL document processor. The media object of “application/x-ncl-settings” type does not have content to be exhibited. Once an NCL application is started, the properties of this media object are available for rule evaluations defined by <rule> elements. In order to use these properties in <link> element definitions, they must be explicitly declared.
  • The application/x-ncl-time (or application/x-ginga-time) type shall be applied to a special <media> element (there may be only one in an NCL document, but it may be reused as child element of other <context> elements), whose content is the UTC. When it is started, the UTC content is not exhibited; however, it can be used to define content anchors by using <area> elements. Note that any continuous <media> element with no source specified can be used to define a clock relative to the <media> element start time.

Reuse of media objects

Excepting <media> elements of “application/x-ncl-NCL” and “application/x-ncl-NCLua” types, a <media> element may refer to another <media> element of the same document or to an imported <media> element. All attributes and child elements defined by the referred element are inherited by the referring element, except the focusIndex attribute. All attributes and child elements defined by the referring element must be ignored by the NCL player, except the following attributes and child elements:

  • id attribute, which shall be defined.
  • instance attribute, which may be defined, otherwise has “new” as its default string value;
  • Child <area> elements may be added. If the new added <area> element has the same id attribute of an already existent <area> element (defined in the reused <media> element), the new added <area> is ignored by the NCL player.
  • Child <property> elements may be added. If the new added <property> element has the same name attribute of an already existing <property> element (defined in the reused <media> element), the new added <property>is ignored by the NCL player.

The referred element and the element that refers to it shall be considered the same, regarding its data specification. They shall also be considered the same regarding their presentation, if the instance attribute receives the “instSame” or “gradSame” values.

The following semantics must be respected when reusing a <media> element. Assume the set of <media> elements composed of the referred <media> element and all the referring <media> elements.

  • If any element of the subset formed by the referred <media> element and all other <media> elements having the instance attribute equal to “instSame” or “gradSame” is scheduled to be presented, all other elements in this subset, which are not descendants of a <switch> element, are also assumed as scheduled for presenting, and more than that, when they are being presented, they are represented by the same presentation instance. Descendant elements of a <switch> element have the same behavior if the rules needed to present them are satisfied, otherwise they are not scheduled for presenting.
    • If the instance attribute is equal to “instSame”, all scheduled nodes of the subset are immediately presented through a unique instance (start instruction applied on all of them) if a start instruction is applied in any of them.
    • If the instance attribute is equal to “gradSame”, all scheduled nodes of the subset are presented through a unique instance, but now gradually, as soon as start instructions are applied on them, coming from a link, etc.
    • As each <media> element starts its presentation,the common instance in presentation must notify the events associated with its <area> and <property> elements.
  • The <media> elements in the set that have instance attribute values equal to “new” are not scheduled for presenting if any other element in the set is scheduled to be presented. When they are individually scheduled for presenting, no other element in the set is affected. Moreover, new independent presentation instances shall be created at each individual presentation starting.

Syntax

Element Attributes Content Parent
<media> id, src, type, refer, instance, descriptor (<area> | <property>)* <body> or <context> or <switch>

Attributes

Name Value Description
id It may receive any string value that begins with a letter or an underscore and that only contains letters, digits, “.”, and “_”. The id attribute uniquely identifies the element within a document.
src

The following are valid values:

  • “file:///file_path/#fragment_identifier” – for local files,
  • “http://server_identifier/file_path/#fragment_identifier” – for remote files downloaded using the HTTP protocol,
  • “https://server_identifier/file_path/#fragment_identifier” – for remote files downloaded using the HTTPS protocol,
  • “rtsp://server_identifier/file_path/#fragment_identifier” – for streams downloaded using the RTSP protocol,
  • “rtp://server_identifier/file_path/#fragment_identifier” – for streams downloaded using the RTP protocol,
  • “ncl-mirror://media_element_identifier” – for a content flow identical to the one in presentation by another <media> element,
  • “sbtvd-ts:” or “isdb-ts:” or “ts://program_number.component_tag” – for elementary streams received from the transport stream.

For src attribute whose value identifies the “sbtvd-ts”, “isdb-ts”, or “ts” scheme, the “program_number.component_tag”, can be substituted by the following reserved words:

  • “video” – corresponding to the primary video ES being presented on the video plan,
  • “audio” – corresponding to the primary audio ES,
  • “text” – corresponding to the primary text ES,
  • “video(i)” – corresponding to the i-th smaller video ES “component_tag” listed in the PMT of the tuned services,
  • “audio(i)” – corresponding to the i-th smaller audio ES “component_tag” listed in the PMT of the tuned services, or
  • “text(i)” – corresponding to the i-th smaller text ES “component_tag” listed in the PMT of the tuned services.
 The src attribute is the locator for the media object content.
type

String.

It shall follow MIME Media Types format. Four special types are defined: “application/x-ncl-NCL” (or “application/x-ginga-NCL”), “application/x-ncl-NCLua” (or “application/x-ginga-NCLua”), “application/x-ncl-settings” (or “application/x-ginga-settings”), and “application/x-ncl-time” (or “application/x-ginga-time”).

 The type attribute shall follow MIME Media Types format (or, more simply, mimetypes). A mimetype is a string that defines the class of media (audio, video, image, text, application) and a media encoding type (such as jpeg, mpeg, etc.). Mimetypes may be registered or informal. Registered mimetypes are controlled by the IANA. Informal mimetypes are not registered with IANA, but are defined by common agreement; they usually have an “x-” before the media type name.
refer IDREF or the string “alias#id” where “id” is an IDREF value.

The refer attribute refers to a <media> element id that will be reused. An element that refers to another element cannot be reused; that is, its id cannot be the value of any refer attribute. The referred element must be a <media> element.

The referred element and the element that refers to it is considered the same regarding their data specification.

If the referred media object is defined within an imported document D, the refer attribute value must have the format “alias#id”, where “alias” is the value of the alias attribute associated with the imported D document.
instance “new”, “instSame”, or “gradSame”. Specifies the reuse type. The “new” value defines a new presentation instance but inheriting the specification of the referred <media> element. The “instSame” value defines a same presentation instance that is immediately started as soon as the referred <media> element or any other <media> elements referring to it with instance attribute equal to “instSame” is started, or if a start instruction is applied on it. The “gradSame” value defines a same presentation instance that is started as soon an start instruction is applied on it, coming from a link, etc.
descriptor IDREF. The descriptor attribute refers to a <descriptor> element.
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