Definition of subtitles omits progression in media time

Current definition of subtitles:

written text that is offered in the audiovisual content, which aims to account for the spoken words of the content, or the spoken words of the content as well as other elements of the soundtrack

Problems with the current definition

I have several problems with this definition:

1. It is too inclusive of other forms of text that would not be considered subtitles, such as transcripts. This is because it does not mention that the text needs to change as the audiovisual content progresses - there is no time aspect in this definition.
2. The phrase "in the audiovisual content" could be interpreted as meaning that it only includes open (burned in) subtitles, such as those that are commonly provided for translation, and not closed subtitles, provided as a timed text data track for presentation by the playback device.
3. It prioritises spoken words, instead of simply being an alternative form of the audio.

I understand that there has been significant debate about this definition, in which I have not participated until now, so there may be some concerns that I'm unaware of - apologies in advance.

Proposed alternative

I would propose something a little different:

text-based alternative to the audio, with timings related to the audiovisual content. Usually includes any spoken words, either in the original language or translated, and can also include descriptions of other sounds or labels to identify features of the audio such as the language being spoken, or the name of the person speaking.

Notes attached to the current text

The current text is also accompanied by 3 notes:

NOTE 1: When subtitles are used as an accommodation for deaf or hard of hearing users, they are also known as captions or as subtitles for the hearing impaired.

NOTE 2: Outside North America, the term Subtitles is often used synonymously with Closed Captions. The term "Hardsubs" is sometimes used in place of Open Captions.

NOTE 3: Subtitles can appear anywhere on the display, and positioned to avoid overlapping content that needs to be visible (such as a "news ticker"), or where the background content would make the subtitles difficult to read.

Note 2 is peculiarly North America-centric. Rather than assuming that Closed Captions is the "normal" term, as it might be in North America, I propose that we recast it as follows:

NOTE 2: The term Subtitles is often used synonymously with what is known in North America as Closed Captions. The term "Hardsubs" is sometimes used in place of Open Captions. Ambiguity can be avoided by qualifying the term "subtitles" with the intended usage, for example "translation subtitles".

Further, no mention is made of typical subtitle features, so I propose that an additional note be added:

NOTE 4: Subtitles can be formatted to aid readability and comprehension, for example by including a background area with a contrasting colour to the foreground text, by specifying the size of the text, by specifying where line breaks occur, or by specifying the typeface used to present the text.