Rendering of ASS subtitles tries to be bug compatible with VSFilter
and stretches fonts when the video is anamorphic (some scripts try to
compensate for this VSFilter behavior, so trying to render them
"correctly" would give the wrong result). However this behavior is not
appropriate for subtitles we converted to ASS format ourselves for
libass rendering, as they certainly don't have VSFilter bug
workarounds. Change the code to use different behavior for "native"
ASS tracks and converted ones. It's questionable whether the
VSFilter-compatible behavior is appropriate for external .ass files
either, as there could be anamorphic and non-anamorphic versions of
the same video and the bug-compatible behavior can only be correct for
one alternative at most. However it's probably better to keep it as a
default at least, so that extracting a muxed subtitle track and using
that does not give behavior different from the original muxed one.
The aspect ratio setting is per ASS_Renderer, and changing it resets
libass caches. For that reason this commit adds separate renderer
instances to use for the "correct" and "VSFilter bug compatible"
cases.
Originally, when rendering plaintext subs with libass, the subtitles
were first converted to the "struct subtitle" form with sub_add_text()
and then from that to libass events. Change sd_ass to convert the
subtitles directly to libass events without using the old sub
machinery. The new conversion at least fixes some timing issues. Also
use the markup support added in the previous commit, so that
HTML-style markup is also supported in "plaintext" subs rendered with
libass.
SubRip subtitles have no "official" spec for any styling support, but
various tags are in common use; previous code filtered out text
between <> to remove HTML-style tags. Add support for those tags and
for MicroDVD subtitle styling. The style display is implemented by
converting the subtitles to the ASS subtitle format and displaying
them with libass, so libass needs to be enabled.
Original patch by Clément Bœsch <ubitux@gmail.com>.
Add a framework for subtitle decoder modules that work more like
audio/video decoders do, and change libass rendering of demuxed
subtitles to use the new framework.
The old subtitle code is messy, with details specific to handling
particular subtitle types spread over high-level code. This should
make it easier to clean things up and fix some bugs/limitations.
