fix(cea708): use dynamic current_fps instead of hardcoded 29.97 in SCC frame delays (#2173)

Replace all 6 hardcoded 1000/29.97 frame delay calculations in
dtvcc_write_scc() with 1000/current_fps so that CEA-708 SCC output
uses the actual stream framerate instead of assuming NTSC 29.97.

Fixes #2172

Author: Atul-Chahar

docs/CHANGES.TXT

@@ -4,6 +4,7 @@
 - Fix: Remove strdup() memory leaks in WebVTT styling encoder, fix invalid CSS rgba(0,256,0) green value, fix missing free(unescaped) on write-error path (#2154)
 - Fix: Prevent crash in Rust timing module when logging out-of-range PTS/FTS timestamps from malformed streams.
 - Fix: Resolve Windows MSVC debug build crash caused by cross-CRT invalid free on Rust-allocated output_filename (#2126)
+- Fix: Use dynamic current_fps instead of hardcoded 29.97 in CEA-708 SCC frame delay calculations (#2172)
 
 0.96.6 (2026-02-19)
 -------------------

src/lib_ccx/ccx_decoders_708_output.c

@@ -550,11 +550,11 @@ void dtvcc_write_scc(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, s
 	if (tv->old_cc_time_end > time_show.time_in_ms)
 	{
 		// Correct the frame delay
-		time_show.time_in_ms -= 1000 / 29.97;
+		time_show.time_in_ms -= 1000 / current_fps;
 		print_scc_time(time_show, buf);
 		buf_len = strlen(buf);
 		SCC_SNPRINTF("\t942c 942c");
-		time_show.time_in_ms += 1000 / 29.97;
+		time_show.time_in_ms += 1000 / current_fps;
 		// Clear the buffer and start pop on caption
 		SCC_SNPRINTF("94ae 94ae 9420 9420");
 	}
@@ -566,20 +566,20 @@ void dtvcc_write_scc(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, s
 		buf_len = strlen(buf);
 		SCC_SNPRINTF("\t942c 942c \n\n");
 		// Correct the frame delay
-		time_show.time_in_ms -= 1000 / 29.97;
+		time_show.time_in_ms -= 1000 / current_fps;
 		// Clear the buffer and start pop on caption in new time
 		print_scc_time(time_show, buf + buf_len);
 		buf_len = strlen(buf);
 		SCC_SNPRINTF("\t94ae 94ae 9420 9420");
-		time_show.time_in_ms += 1000 / 29.97;
+		time_show.time_in_ms += 1000 / current_fps;
 	}
 	else
 	{
-		time_show.time_in_ms -= 1000 / 29.97;
+		time_show.time_in_ms -= 1000 / current_fps;
 		print_scc_time(time_show, buf);
 		buf_len = strlen(buf);
 		SCC_SNPRINTF("\t942c 942c 94ae 94ae 9420 9420");
-		time_show.time_in_ms += 1000 / 29.97;
+		time_show.time_in_ms += 1000 / current_fps;
 	}
 
 	int total_subtitle_count = count_captions_lines_scc(tv);