feat: add 23.98fps as valid --scc-framerate value and fix help text

- Add case 4 (23.976f) to both get_scc_fps() and get_scc_fps_internal()
  in ccx_encoders_scc.c so --scc-framerate 23.98 produces correct output
- Add "23.98" | "23.976" match arm in parser.rs mapping to value 4
- Add test_scc_framerate_23_98() unit test in parser.rs
- Update --scc-framerate help text to clarify it affects both input
  parsing AND output encoding (not input only)
- Add 23.98 to the listed valid values in the help text

Follows up on discussion in #2145 and #2146.

docs/CHANGES.TXT

@@ -1,5 +1,6 @@
 0.96.6 (2026-02-19)
 -------------------
+- New: Add 23.98fps as valid --scc-framerate value; clarify help text covers input and output (#2147)
 - FIX: spupng start numbering at sub0000, avoid index advance on empty EOD, normalize header filename
 - New: 32-bit (x86) Windows build and installer (#2116)
 - New: Add optional machine-readable JSON output for -out=report via --report-format json

src/lib_ccx/ccx_encoders_scc.c

@@ -21,7 +21,7 @@ unsigned char odd_parity(const unsigned char byte)
  */
 
 // Get frame rate value from scc_framerate setting
-// 0=29.97 (default), 1=24, 2=25, 3=30
+// 0=29.97 (default), 1=24, 2=25, 3=30, 4=23.98
 static float get_scc_fps_internal(int scc_framerate)
 {
 	switch (scc_framerate)
@@ -32,6 +32,8 @@ static float get_scc_fps_internal(int scc_framerate)
 			return 25.0f;
 		case 3:
 			return 30.0f;
+		case 4:
+			return 23.976f;
 		default:
 			return 29.97f;
 	}
@@ -827,7 +829,7 @@ enum control_code get_font_code(enum font_bits font, enum ccx_decoder_608_color_
 }
 
 // Get frame rate value from scc_framerate setting
-// 0=29.97 (default), 1=24, 2=25, 3=30
+// 0=29.97 (default), 1=24, 2=25, 3=30, 4=23.98
 static float get_scc_fps(int scc_framerate)
 {
 	switch (scc_framerate)
@@ -838,6 +840,8 @@ static float get_scc_fps(int scc_framerate)
 			return 25.0f;
 		case 3:
 			return 30.0f;
+		case 4:
+			return 23.976f;
 		default:
 			return 29.97f;
 	}

src/rust/src/args.rs

@@ -296,8 +296,8 @@ pub struct Args {
     /// DVD Recorder)
     #[arg(long="90090", verbatim_doc_comment, help_heading=OPTIONS_AFFECTING_INPUT_FILES)]
     pub mpeg90090: bool,
-    /// Set the frame rate for SCC (Scenarist Closed Caption) input files.
-    /// Valid values: 29.97 (default), 24, 25, 30
+    /// Set the frame rate for Scenarist Closed Captioning (SCC) input parsing and output encoding.
+    /// Valid values: 23.98, 29.97 (default), 24, 25, 30
     /// Example: --scc-framerate 25
     #[arg(long="scc-framerate", verbatim_doc_comment, value_name="fps", help_heading=OPTIONS_AFFECTING_INPUT_FILES)]
     pub scc_framerate: Option<String>,

src/rust/src/parser.rs

@@ -839,6 +839,7 @@ impl OptionsExt for Options {
         if let Some(ref fps_str) = args.scc_framerate {
             self.scc_framerate = match fps_str.as_str() {
                 "29.97" | "29" => 0,
+                "23.98" | "23.976" => 4,
                 "24" => 1,
                 "25" => 2,
                 "30" => 3,
@@ -2830,6 +2831,11 @@ pub mod tests {
         assert_eq!(options.scc_framerate, 0);
     }
 
+    #[test]
+    fn test_scc_framerate_23_98() {
+        let (options, _) = parse_args(&["--scc-framerate", "23.98"]);
+        assert_eq!(options.scc_framerate, 4);
+    }
     #[test]
     fn test_scc_framerate_24() {
         let (options, _) = parse_args(&["--scc-framerate", "24"]);