sd_srt, sd_microdvd: set ASS script resolution

Both converters can output \pos and deal with font sizes, so they assume
a specific script resolution (PlayResX/PlayResY). The implicit
assumption was that a specific resolution was guaranteed. The
MP_ASS_FONT_PLAYRESY constant is connected to this.

Better make it explicit, so that the implicit dependency on
MP_ASS_FONT_PLAYRESY is removed. (Unfortunately, libavcodec sub
converters still don't set PlayResX/PlayResY explicitly, so the value
set by that constant can't be declared as arbitrary yet.)

PlayResY=288 is most likely the SSA natural script resolution (or
something like this?), as well as the libass and VSFilter default.
PlayResX=384 is the fallback value set by libass if PlayResY is set to
288, and PlayResX is unset.

1 files changed, 8 insertions, 0 deletions

diff --git a/sub/sd_srt.c b/sub/sd_srt.c
index fcad088dc1..6258acde5b 100644
--- a/sub/sd_srt.c
+++ b/sub/sd_srt.c
@@ -437,6 +437,12 @@ static void convert_subrip(const char *orig, char *dest, int dest_buffer_size)
     new_line.buf[new_line.len] = 0;
 }
 
+static const char *srt_ass_extradata =
+    "[Script Info]\n"
+    "ScriptType: v4.00+\n"
+    "PlayResX: 384\n"
+    "PlayResY: 288\n";
+
 static bool supports_format(const char *format)
 {
     return format && (strcmp(format, "subrip") == 0 ||
@@ -446,6 +452,8 @@ static bool supports_format(const char *format)
 static int init(struct sd *sd)
 {
     sd->output_codec = "ass-text";
+    sd->output_extradata = (char *)srt_ass_extradata;
+    sd->output_extradata_len = strlen(sd->output_extradata);
     return 0;
 }