sub: add an option to filter subtitles by regex

Works as ad-filter. I had some more plans, for example replacing
matching text with different text, but for now it's dropping matches
only. There's a big warning in the manpage that I might change
semantics. For example, I might turn it into a primitive sed.

In a sane world, you'd probably write a simple script that processes
downloaded subtitles before giving them to mpv, and avoid all this
complexity. But we don't live in a sane world, and the sooner you learn
this, the happier you will be. (But I also want to run this on muxed
subtitles.)

This is pretty straightforward. We use POSIX regexes, which are readily
available without additional pain or dependencies. This also means it's
(apparently) not available on win32 (MinGW). The regex list is because I
hate big monolithic regexes, and this makes it slightly better.

Very superficially tested.

1 files changed, 3 insertions, 0 deletions

diff --git a/sub/sd_ass.c b/sub/sd_ass.c
index 2b0cf13127..40e5093d8e 100644
--- a/sub/sd_ass.c
+++ b/sub/sd_ass.c
@@ -65,6 +65,9 @@ static void fill_plaintext(struct sd *sd, double pts);
 static const struct sd_filter_functions *const filters[] = {
     // Note: list order defines filter order.
     &sd_filter_sdh,
+#if HAVE_POSIX
+    &sd_filter_regex,
+#endif
     NULL,
 };