1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
|
# Data model
## Overall
The canonical model closely follows the [TTML 2](https://www.w3.org/TR/ttml2) data model, as constrained by the [IMSC 1.1 Text Profile](https://www.w3.org/TR/ttml-imsc1.1/#text-profile) specification. This includes both the static structure of the model as well as temporal, layout and style processing. The objective is for a valid IMSC 1.1 Text Profile document to be mapped into a canonical model instance such that presenting instance results in the same outout as the input IMSC document.
The canonical model is specified in `ttconv.model`.
The class hierarchy of the canonical model is summarized the following figure:
```txt
ContentDocument
: Region* Body?
Body
: Div*
Div
: (P | Div)*
P
: (Span | Ruby | Br)*
Span
: (Span | Br | Text)*
Ruby
: Rb? Rt?
| Rb? Rp Rt? Rp
| Rbc Rtc Rtc?
Rbc
: Rb*
Rtc
: Rt*
| Rp Rt* Rp
Rb, Rt, Rp
: Span*
```
where:
* the `ContentDocument` class corresponds to the `tt` element
* the `Body`, `Div`, `P`, `Span`, `Br` and `Region` classes corresponds to the TTML content element of the same name, respectively
* the `Text` class corresponds to a TTML text node
* the `Ruby`, `Rt`, `Rb`, `Rtc`, `Rbc`, `Rp` classes correspond to the TTML `span` element with the computed value of `tts:ruby` attribute specified in the following table
| Canonical model class | Computed value of `tts:ruby` attribute |
|-----------------------|----------------------------------------|
| `Ruby` | `container` |
| `Rt` | `text` |
| `Rb` | `base` |
| `Rtc` | `textContainer` |
| `Rbc` | `baseContainer` |
| `Rp` | `delimiter` |
## Basic operation
The canonical model allows content elements (instances of `ttconv.model.ContentElement`) to be arranged in a hierarchical structures (using the `ttconv.model.ContentElement.push_child()` and `ttconv.model.ContentElement.remove_child()`) that are associated with a single document (using the `ttconv.model.ContentElement.set_doc()` method with an instance of `ttconv.model.ContentDocument`).
## Divergences with the TTML data model
### Initial values
The TTML `initial` elements are accessed using the `ContentDocument.set_initial_value()` and `ContentDocument.get_initial_value()` method.
### Styling
Style properties are access using the `ContentElement.get_style()` and `ContentElement.set_style()` methods.
The style properties themselves are defined in `ttconv.style_properties`, where the lower camel case names used in TTML are replaced by their equivalent in upper camel case. Deprecated style properties, e.g. `tts:zIndex` are not supported.
Only _inline styling_ of content elements is supported, and neither _referential sytling_ nor _chained referential styling_ nor _nested styling_ are supported.
### Metadata
TTML `metadata` elements are not supported.
### Timing
Only _parallel time container_ semantics are supported and temporal offsets are expressed as `fractions.Fraction` instances in seconds. As a result, the following parameters are not supported: `ttp:frameRate`, `ttp:frameRateMultiplier`, `ttp:subFrameRate`, `ttp:tickRate`.
Writer module can express temporal offsets in units of ticks, frames, etc. as demanded by the output format or configured by the user.
The `dur` timing attribute is not supported.
### Lengths
Extent, origin and position lengths can be expressed in `c`, `%`, `rh`, `rw` and `px` units.
|
