diff mbox series

[FFmpeg-devel,v3,3/4] avcodec/{ass, webvttdec}: more portable curly brace escapes

Message ID 20240212020159.6806-4-oneric@oneric.de
State New
Headers show
Series Fix some active sequences in subtitles | expand

Checks

Context Check Description
yinshiyou/make_loongarch64 success Make finished
yinshiyou/make_fate_loongarch64 fail Make fate failed
andriy/make_x86 success Make finished
andriy/make_fate_x86 fail Make fate failed

Commit Message

Oneric Feb. 12, 2024, 2:01 a.m. UTC 
Unlike what the old comment suggested, standard ASS has no character
escape mechanism, but a closing curly bracket doesn't even need one.

For manual authored sub files using a full-width variant of an apropiate
font and with scaling and psacing modifiers is a common workaround.
This is not an option here, but we can still make things much less bad.
Now the desired opening bracket still shows up in libass and
standard renders will merely display a backslash in its place
instead of stripping the following text like before.
---
 libavcodec/ass.c          | 12 ++++++++----
 libavcodec/webvttdec.c    |  2 +-
 tests/ref/fate/sub-webvtt |  2 +-
 3 files changed, 10 insertions(+), 6 deletions(-)
diff mbox series

Patch

diff --git a/libavcodec/ass.c b/libavcodec/ass.c
index a68d3568b4..e7a1ac0eb5 100644
--- a/libavcodec/ass.c
+++ b/libavcodec/ass.c
@@ -181,10 +181,14 @@  void ff_ass_bprint_text_event(AVBPrint *buf, const char *p, int size,
         if (linebreaks && strchr(linebreaks, *p)) {
             av_bprintf(buf, "\\N");
 
-        /* standard ASS escaping so random characters don't get mis-interpreted
-         * as ASS */
-        } else if (!keep_ass_markup && strchr("{}", *p)) {
-            av_bprintf(buf, "\\%c", *p);
+        /* cancel curly brackets to avoid bogus override tag blocks
+         * hiding text. Standard ASS has no character escapes,
+         * though (only) libass provides \{ and \}.
+         * Unpaired closing brackets don't need escaping at all though and
+         * to make the situation less bad in standard ASS insert an empty block
+         */
+        } else if (!keep_ass_markup && *p == '{') {
+            av_bprintf(buf, "\\{{}");
 
         /* append word-joiner U+2060 as UTF-8 to break up sequences like \N */
         } else if (!keep_ass_markup && *p == '\\') {
diff --git a/libavcodec/webvttdec.c b/libavcodec/webvttdec.c
index 6e55bc5499..35bdbe805d 100644
--- a/libavcodec/webvttdec.c
+++ b/libavcodec/webvttdec.c
@@ -37,7 +37,7 @@  static const struct {
     {"<i>", "{\\i1}"}, {"</i>", "{\\i0}"},
     {"<b>", "{\\b1}"}, {"</b>", "{\\b0}"},
     {"<u>", "{\\u1}"}, {"</u>", "{\\u0}"},
-    {"{", "\\{"}, {"}", "\\}"}, {"\\", "\\\xe2\x81\xa0"}, // escape to avoid ASS markup conflicts
+    {"{", "\\{{}"}, {"\\", "\\\xe2\x81\xa0"}, // escape to avoid ASS markup conflicts
     {"&gt;", ">"}, {"&lt;", "<"},
     {"&lrm;", "\xe2\x80\x8e"}, {"&rlm;", "\xe2\x80\x8f"},
     {"&amp;", "&"}, {"&nbsp;", "\\h"},
diff --git a/tests/ref/fate/sub-webvtt b/tests/ref/fate/sub-webvtt
index ea587b327c..fae50607fb 100644
--- a/tests/ref/fate/sub-webvtt
+++ b/tests/ref/fate/sub-webvtt
@@ -21,7 +21,7 @@  Dialogue: 0,0:00:22.00,0:00:24.00,Default,,0,0,0,,at the AMNH.
 Dialogue: 0,0:00:24.00,0:00:26.00,Default,,0,0,0,,Thank you for walking down here.
 Dialogue: 0,0:00:27.00,0:00:30.00,Default,,0,0,0,,And I want to do a follow-up on the last conversation we did.\Nmultiple lines\Nagain
 Dialogue: 0,0:00:30.00,0:00:31.50,Default,,0,0,0,,When we e-mailed—
-Dialogue: 0,0:00:30.50,0:00:32.50,Default,,0,0,0,,Didn't we {\b1}talk {\i1}about\N{\i0} enough{\b0} in that conversation? \{I'm not an ASS comment\}
+Dialogue: 0,0:00:30.50,0:00:32.50,Default,,0,0,0,,Didn't we {\b1}talk {\i1}about\N{\i0} enough{\b0} in that conversation? \{{}I'm not an ASS comment}
 Dialogue: 0,0:00:32.00,0:00:35.50,Default,,0,0,0,,No! No no no no; 'cos 'cos obviously 'cos
 Dialogue: 0,0:00:32.50,0:00:33.50,Default,,0,0,0,,{\i1}Laughs{\i0}
 Dialogue: 0,0:00:35.50,0:00:38.00,Default,,0,0,0,,You know I'm so excited my glasses are falling off here.