Strictly speaking, the TTML spec requires that text backgrounds extend
only to the font height of the related text, rather than to the vertical
distance between lines. The result of this is that there will typically
be vertical gaps between line backgrounds through which moving video can
be seen. Since this was unnacceptable to some content providers, v1.0.1
of the IMSC spec (which profiles TTML) adds a new attribute,
itts:fillLineGap[1], that allows content authors to specify that clients
should extend text backgrounds such that there are no gaps between
lines. This attribute is also going to be included in the next release
of EBU-TT-D.
This patch adds support for fillLineGap to ttmlparse and ttmlrender.
[1] https://www.w3.org/TR/ttml-imsc1.0.1/#itts-fillLineGaphttps://bugzilla.gnome.org/show_bug.cgi?id=787071
Clang's static analyser found potential code paths in which variables
were being used in comparisons when uninitialised. Fix by properly
handling out-of-range value returned by gst_ttml_get_element_index.
The specified behaviour in TTML when lineHeight is "normal" is different
from the behaviour when a percentage is given. In the former case, the
line height is a percentage (the TTML spec recommends 125%) of the largest
font size that is applied to the spans within the block; in the latter
case, the line height is the given percentage of the font size that is
applied to the block itself.
The code doesn't correctly implement this behaviour; this patch fixes
that.
https://bugzilla.gnome.org/show_bug.cgi?id=780402
In TTML, the height of every line in a block is determined by lineHeight
and fontSize style attributes, and should be the same for each line in
that block, regardless of whether different sized text appears on
different lines. Currently, a single PangoLayout is used to lay out all
the text in a block; however, pango will vary the line height in a
layout depending on the size of text used in each line, which is not
compliant with TTML.
This patch makes ttmlrender lay out the lines in a block itself, rather
than using a PangoLayout to do the work. The code still uses a
PangoLayout to render the text of each element, but the overall layout
of the text in a block is now controlled by ttmlrender itself. By doing
this, ttmlrender is able to ensure that the height of each line in a
block is correct.
https://bugzilla.gnome.org/show_bug.cgi?id=780402
