lavfi/subtitles: add force_style option

Signed-off-by: Eejya Singh <singh.eejya@gmail.com>
Signed-off-by: Clément Bœsch <u@pkh.me>

doc/filters.texi

@@ -8554,6 +8554,10 @@ useful if not UTF-8.
 
 @item stream_index, si
 Set subtitles stream index. @code{subtitles} filter only.
+
+@item force_style
+Override default style or script info parameters of the subtitles. It accepts a
+string containing ASS style format @code{KEY=VALUE} couples separated by ",".
 @end table
 
 If the first key is not specified, it is assumed that the first value
@@ -8580,6 +8584,12 @@ To render the second subtitles stream from that file, use:
 subtitles=video.mkv:si=1
 @end example
 
+To make the subtitles stream from @file{sub.srt} appear in transparent green
+@code{DejaVu Serif}, use:
+@example
+subtitles=sub.srt:force_style='FontName=DejaVu Serif,PrimaryColour=&HAA00FF00'
+@end example
+
 @section super2xsai
 
 Scale the input by 2x and smooth using the Super2xSaI (Scale and

libavfilter/version.h

@@ -31,7 +31,7 @@
 
 #define LIBAVFILTER_VERSION_MAJOR  5
 #define LIBAVFILTER_VERSION_MINOR  9
-#define LIBAVFILTER_VERSION_MICRO 103
+#define LIBAVFILTER_VERSION_MICRO 104
 
 #define LIBAVFILTER_VERSION_INT AV_VERSION_INT(LIBAVFILTER_VERSION_MAJOR, \
                                                LIBAVFILTER_VERSION_MINOR, \

libavfilter/vf_subtitles.c

@@ -51,6 +51,7 @@ typedef struct {
     ASS_Track    *track;
     char *filename;
     char *charenc;
+    char *force_style;
     int stream_index;
     uint8_t rgba_map[4];
     int     pix_step[4];       ///< steps per pixel for each plane of the main output
@@ -260,6 +261,7 @@ static const AVOption subtitles_options[] = {
     {"charenc",      "set input character encoding", OFFSET(charenc),      AV_OPT_TYPE_STRING, {.str = NULL}, CHAR_MIN, CHAR_MAX, FLAGS},
     {"stream_index", "set stream index",             OFFSET(stream_index), AV_OPT_TYPE_INT,    { .i64 = -1 }, -1,       INT_MAX,  FLAGS},
     {"si",           "set stream index",             OFFSET(stream_index), AV_OPT_TYPE_INT,    { .i64 = -1 }, -1,       INT_MAX,  FLAGS},
+    {"force_style",  "force subtitle style",         OFFSET(force_style),  AV_OPT_TYPE_STRING, {.str = NULL}, CHAR_MIN, CHAR_MAX, FLAGS},
     {NULL},
 };
 
@@ -392,6 +394,27 @@ static av_cold int init_subtitles(AVFilterContext *ctx)
     if (ret < 0)
         goto end;
 
+    if (ass->force_style) {
+        char **list = NULL;
+        char *temp = NULL;
+        char *ptr = av_strtok(ass->force_style, ",", &temp);
+        int i = 0;
+        while (ptr) {
+            av_dynarray_add(&list, &i, ptr);
+            if (!list) {
+                ret = AVERROR(ENOMEM);
+                goto end;
+            }
+            ptr = av_strtok(NULL, ",", &temp);
+        }
+        av_dynarray_add(&list, &i, NULL);
+        if (!list) {
+            ret = AVERROR(ENOMEM);
+            goto end;
+        }
+        ass_set_style_overrides(ass->library, list);
+        av_free(list);
+    }
     /* Decode subtitles and push them into the renderer (libass) */
     if (dec_ctx->subtitle_header)
         ass_process_codec_private(ass->track,