The Encoding field (and the \fe tag) allows to limit font selection to
only those fonts declaring support for the specified codepage in their
OS/2's table "Code Page Character Range" field.
Particularly, Encoding=0 means only font's declaring support for "ANSI",
or rather "Latin (Western European)", are allowed to be selected.
Specifying Encoding=1 allows all fonts to be considered.
We do not want to limit font selection, so specify Encoding=1.
NB: at the time of writing libass only partially supports this field,
thus hiding the issue in any libass-based renderer. A VSFilter-based
DirectShow filter or XySubFilter will reveal the issue when a font not
declaring support for latin characters is specified in a style.
Colour values used in ASS files without a "YCbCr Matrix" header set to
"None" are subject to colour mangling, due to how ASS was historically
conceived. A more in-depth description can be found in the documetation
inside libass' public ass_types.h header. The important part is, if this
header is not set to "None", the final output colours can deviate from
the literal value specified in the file. When converting from non-ASS
formats we do not want any colour shift to happen, so let's set the
appropiate header.
NB: ffmpeg's subtitle filter, does not follow libass' documentation
regarding colour mangling, thus hiding the bug. Anything based on
VSFilter, XySubFilter or e.g. mpv do and might show the issue.
(Of course native ASS subs, which _do_ rely on colour mangling won't
work properly with the subtitle filter, but this can be fixed another
time)
This commit switches off forced correct nesting of tags and only keeps
it for font tags. See long explanations in the code for the rationale.
This results in various FATE changes which I'll explain here:
- various swapping in font attributes, this is mostly noise due to the
old reverse stack way of printing them. The new one is more correct as
the last attribute takes over the previous ones.
- unrecognized tags disappears
- invalid tags that were previously displayed aren't anymore (instead,
we have a warning). This is better for the end user
The main benefit of this commit is to be more tolerant to error, leading
to a better handling of badly nested tags or random wrong formatting for
the end user.
The positioning was completely wrong. First, the coordinates are
expressed in ASS playback resolution (which is by default 384x288).
Secondly, the coordinates define a drawing rectangle, not a moving area.
The previous code was making subtitles move from a random position to
another random position.
Here we rescale assuming the video resolution is a DVD one (720x480). We
can't really do anything better so far, but since this positioning
information is often from a DVD rip we can consider them relatively
safe.
This avoids the following libass warning when using the subtitles
filter: "Neither PlayResX nor PlayResY defined. Assuming 384x288"
Subtitles tests change because the output is ASS and the PlayRes[XY]
ends up in the output.
The "Default" style written in the header is ignored unless you explicit
it in the Dialogue events (it was valid, just ignored). This requires an
update of the SubRip test since the ASS output obviously changes.
Oneric
Clément Bœsch
Clément Bœsch
Aurelien Jacobs