[FEATURE] Add SCC support to CEA-708 decoder (#1595)

* feat: Add timing functions for SCC format in C & Rust

* feat: Add SCC support to Rust 708 decoder

* feat: Add SCC support to C 708 decoder

* docs: fix symbol in scc_time format

* chore: clippy fixes

* docs: Add new feature in Changelog

* fix: update SCC timing functions according to need

* feat: Add new member(old caption end time) for overlapping situations

* fix: update SCC timing functions according to need

* feat: Add support for overlapping captions situations

* fix: frame formula for timings

* feat: Add support for orientation of subtitles in C

by adding necessary labels needed for it

* feat: Add support for orientation of subtitles in Rust

by adding necessary labels needed for it

* docs: Add info for scc labels

* chore: clippy fixes

* docs: Add what `add_needed_scc_labels` do and correct parameters name

docs/CHANGES.TXT

@@ -1,5 +1,6 @@
 0.95 (to be released)
 -----------------
+- New: Add SCC support for CEA-708 decoder (#1595)
 - Fix: respect `-stdout` even if multiple CC tracks are present in a Matroska input file (#1453)
 - Fix: crash in Rust decoder on ATSC1.0 TS Files (#1407)
 - Removed the --with-gui flag for linux/configure and mac/configure (use the Flutter GUI instead)

src/lib_ccx/ccx_common_timing.c

@@ -295,6 +295,34 @@ LLONG get_fts_max(struct ccx_common_timing_ctx *ctx)
 	return ctx->fts_max + ctx->fts_global;
 }
 
+/**
+ * SCC Time formatting
+ */
+size_t print_scc_time(struct ccx_boundary_time time, char *buf)
+{
+	char *fmt = "%02u:%02u:%02u;%02u";
+	double frame;
+
+	frame = ((double)(time.time_in_ms - 1000 * (time.ss + 60 * (time.mm + 60 * time.hh))) * 29.97 / 1000);
+
+	return (size_t)sprintf(buf + time.set, fmt, time.hh, time.mm, time.ss, (unsigned)frame);
+}
+
+struct ccx_boundary_time get_time(LLONG time)
+{
+	if (time < 0) // Avoid loss of data warning with abs()
+		time = -time;
+
+	struct ccx_boundary_time result;
+	result.hh = (unsigned)(time / 1000 / 60 / 60);
+	result.mm = (unsigned)(time / 1000 / 60 - 60 * result.hh);
+	result.ss = (unsigned)(time / 1000 - 60 * (result.mm + 60 * result.hh));
+	result.time_in_ms = time;
+	result.set = (time < 0 ? 1 : 0);
+
+	return result;
+}
+
 /**
  * Fill buffer with a time string using specified format
  * @param fmt has to contain 4 format specifiers for h, m, s and ms respectively

src/lib_ccx/ccx_common_timing.h

@@ -77,6 +77,8 @@ struct ccx_common_timing_ctx *init_timing_ctx(struct ccx_common_timing_settings_
 
 void set_current_pts(struct ccx_common_timing_ctx *ctx, LLONG pts);
 void add_current_pts(struct ccx_common_timing_ctx *ctx, LLONG pts);
+struct ccx_boundary_time get_time(LLONG mstime);
+size_t print_scc_time(struct ccx_boundary_time time, char *buf);
 int set_fts(struct ccx_common_timing_ctx *ctx);
 LLONG get_fts(struct ccx_common_timing_ctx *ctx, int current_field);
 LLONG get_fts_max(struct ccx_common_timing_ctx *ctx);

src/lib_ccx/ccx_decoders_708.h

@@ -302,6 +302,7 @@ typedef struct dtvcc_tv_screen
 	LLONG time_ms_hide;
 	unsigned int cc_count;
 	int service_number;
+	int old_cc_time_end;
 } dtvcc_tv_screen;
 
 /**

src/lib_ccx/ccx_decoders_708_output.c

@@ -367,6 +367,155 @@ void dtvcc_write_sami(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder,
 	write_wrapped(encoder->dtvcc_writers[tv->service_number - 1].fd, buf, strlen(buf));
 }
 
+unsigned char adjust_odd_parity(const unsigned char value)
+{
+	unsigned int i, ones = 0;
+	for (i = 0; i < 8; i++)
+	{
+		if ((value & (1 << i)) != 0)
+		{
+			ones += 1;
+		}
+	}
+	if (ones % 2 == 0)
+	{
+		// make the number of ones always odd
+		return value | 0b10000000;
+	}
+	return value;
+}
+
+void dtvcc_write_scc_header(dtvcc_tv_screen *tv, struct encoder_ctx *encoder)
+{
+	char *buf = (char *)encoder->buffer;
+	// 18 characters long + 2 new lines
+	memset(buf, 0, 20);
+	sprintf(buf, "Scenarist_SCC V1.0\n\n");
+
+	write_wrapped(encoder->dtvcc_writers[tv->service_number - 1].fd, buf, strlen(buf));
+}
+
+int count_captions_lines_scc(dtvcc_tv_screen *tv)
+{
+	int count = 0;
+	for (int i = 0; i < CCX_DTVCC_SCREENGRID_ROWS; i++)
+	{
+		if (!dtvcc_is_row_empty(tv, i))
+		{
+			count++;
+		}
+	}
+
+	return count;
+}
+
+/** This function is designed to assign appropriate SSC labels for positioning subtitles based on their length.
+ * In some scenarios where the video stream provides lengthy subtitles that cannot fit within a single line.
+ * Single-line subtitle can be placed in 15th row(most bottom row)
+ * 2 line length subtitles can be placed in 14th and 15th row
+ * 3 line length subtitles can be placed in 13th, 14th and 15th row
+ */
+void add_needed_scc_labels(char *buf, int total_subtitle_count, int current_subtitle_count)
+{
+	switch (total_subtitle_count)
+	{
+		case 1:
+			// row 15, column 00
+			sprintf(buf + strlen(buf), " 94e0 94e0");
+			break;
+		case 2:
+			// 9440: row 14, column 00 | 94e0: row 15, column 00
+			sprintf(buf + strlen(buf), current_subtitle_count == 1 ? " 9440 9440" : " 94e0 94e0");
+			break;
+		default:
+			// 13e0: row 13, column 04 | 9440: row 14, column 00 | 94e0: row 15, column 00
+			sprintf(buf + strlen(buf), current_subtitle_count == 1 ? " 13e0 13e0" : (current_subtitle_count == 2 ? " 9440 9440" : " 94e0 94e0"));
+	}
+}
+
+void dtvcc_write_scc(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder)
+{
+	dtvcc_tv_screen *tv = decoder->tv;
+
+	if (dtvcc_is_screen_empty(tv, encoder))
+		return;
+
+	if (tv->time_ms_show + encoder->subs_delay < 0)
+		return;
+
+	if (tv->cc_count == 2)
+		dtvcc_write_scc_header(tv, encoder);
+
+	char *buf = (char *)encoder->buffer;
+	struct ccx_boundary_time time_show = get_time(tv->time_ms_show + encoder->subs_delay);
+	// when hiding subtract a frame (1 frame = 34 ms)
+	struct ccx_boundary_time time_end = get_time(tv->time_ms_hide + encoder->subs_delay - 34);
+
+	if (tv->old_cc_time_end > time_show.time_in_ms)
+	{
+		// Correct the frame delay
+		time_show.time_in_ms -= 1000 / 29.97;
+		print_scc_time(time_show, buf);
+		sprintf(buf + strlen(buf), "\t942c 942c");
+		time_show.time_in_ms += 1000 / 29.97;
+		// Clear the buffer and start pop on caption
+		sprintf(buf + strlen(buf), "94ae 94ae 9420 9420");
+	}
+	else if (tv->old_cc_time_end < time_show.time_in_ms)
+	{
+		// Clear the screen for new caption
+		struct ccx_boundary_time time_to_display = get_time(tv->old_cc_time_end);
+		print_scc_time(time_to_display, buf);
+		sprintf(buf + strlen(buf), "\t942c 942c \n\n");
+		// Correct the frame delay
+		time_show.time_in_ms -= 1000 / 29.97;
+		// Clear the buffer and start pop on caption in new time
+		print_scc_time(time_show, buf);
+		sprintf(buf + strlen(buf), "\t94ae 94ae 9420 9420");
+		time_show.time_in_ms += 1000 / 29.97;
+	}
+	else
+	{
+		time_show.time_in_ms -= 1000 / 29.97;
+		print_scc_time(time_show, buf);
+		sprintf(buf + strlen(buf), "\t942c 942c 94ae 94ae 9420 9420");
+		time_show.time_in_ms += 1000 / 29.97;
+	}
+
+	int total_subtitle_count = count_captions_lines_scc(tv);
+	int current_subtitle_count = 0;
+
+	for (int i = 0; i < CCX_DTVCC_SCREENGRID_ROWS; i++)
+	{
+		if (!dtvcc_is_row_empty(tv, i))
+		{
+			current_subtitle_count++;
+			add_needed_scc_labels(buf, total_subtitle_count, current_subtitle_count);
+
+			int first, last, bytes_written = 0;
+			dtvcc_get_write_interval(tv, i, &first, &last);
+			for (int j = first; j <= last; j++)
+			{
+				if (bytes_written % 2 == 0)
+					sprintf(buf + strlen(buf), " ");
+				sprintf(buf + strlen(buf), "%x", adjust_odd_parity(tv->chars[i][j].sym));
+				bytes_written += 1;
+			}
+			// if byte pair are not even then make it even by adding 0x80 as padding
+			if (bytes_written % 2 == 1)
+				sprintf(buf + strlen(buf), "80 ");
+			else
+				sprintf(buf + strlen(buf), " ");
+		}
+	}
+
+	// Display caption (942f 942f)
+	sprintf(buf + strlen(buf), "942f 942f \n\n");
+	write_wrapped(encoder->dtvcc_writers[tv->service_number - 1].fd, buf, strlen(buf));
+
+	tv->old_cc_time_end = time_end.time_in_ms;
+}
+
 void dtvcc_write(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder)
 {
 	switch (encoder->write_format)
@@ -382,6 +531,9 @@ void dtvcc_write(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struc
 		case CCX_OF_SAMI:
 			dtvcc_write_sami(writer, decoder, encoder);
 			break;
+		case CCX_OF_SCC:
+			dtvcc_write_scc(writer, decoder, encoder);
+			break;
 		case CCX_OF_MCC:
 			printf("REALLY BAD... [%s:%d]\n", __FILE__, __LINE__);
 			break;

src/lib_ccx/ccx_decoders_708_output.h

@@ -8,11 +8,11 @@
 void dtvcc_write_done(dtvcc_tv_screen *tv, struct encoder_ctx *encoder);
 
 void dtvcc_writer_init(dtvcc_writer_ctx *writer,
-						   char *base_filename,
-						   int program_number,
-						   int service_number,
-						   enum ccx_output_format write_format,
-						   struct encoder_cfg *cfg);
+		       char *base_filename,
+		       int program_number,
+		       int service_number,
+		       enum ccx_output_format write_format,
+		       struct encoder_cfg *cfg);
 void dtvcc_writer_cleanup(dtvcc_writer_ctx *writer);
 void dtvcc_writer_output(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder);
 
@@ -30,6 +30,9 @@ void dtvcc_write_transcript(dtvcc_writer_ctx *writer, dtvcc_service_decoder *dec
 void dtvcc_write_sami_header(dtvcc_tv_screen *tv, struct encoder_ctx *encoder);
 void dtvcc_write_sami_footer(dtvcc_tv_screen *tv, struct encoder_ctx *encoder);
 void dtvcc_write_sami(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder);
+void dtvcc_write_scc_header(dtvcc_tv_screen *tv, struct encoder_ctx *encoder);
+void add_needed_scc_labels(char *buf, int total_subtitle_count, int current_subtitle_count);
+void dtvcc_write_scc(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder);
 void dtvcc_write(dtvcc_writer_ctx *writer, dtvcc_service_decoder *decoder, struct encoder_ctx *encoder);
 
-#endif /*_CCX_DECODERS_708_OUTPUT_H_*/
+#endif /*_CCX_DECODERS_708_OUTPUT_H_*/

src/rust/src/decoder/output.rs

@@ -20,6 +20,7 @@ pub struct Writer<'a> {
     pub no_font_color: bool,
     pub transcript_settings: &'a ccx_encoders_transcript_format,
     pub no_bom: i32,
+    pub old_cc_time_end: i32,
 }
 
 impl<'a> Writer<'a> {
@@ -42,6 +43,7 @@ impl<'a> Writer<'a> {
             no_font_color: is_true(no_font_color),
             transcript_settings,
             no_bom,
+            old_cc_time_end: 0,
         }
     }
     /// Write subtitles to the file

src/rust/src/decoder/timing.rs

@@ -47,3 +47,31 @@ pub fn get_time_str(time: LLONG) -> String {
     let ms = time - 1000 * (ss + 60 * (mm + 60 * hh));
     format!("{:02}:{:02}:{:02},{:03}", hh, mm, ss, ms)
 }
+
+impl ccx_boundary_time {
+    /// Returns ccx_boundary_time from given time
+    pub fn get_time(time: LLONG) -> Self {
+        let hh = time / 1000 / 60 / 60;
+        let mm = time / 1000 / 60 - 60 * hh;
+        let ss = time / 1000 - 60 * (mm + 60 * hh);
+
+        Self {
+            hh: hh as i32,
+            mm: mm as i32,
+            ss: ss as i32,
+            time_in_ms: time,
+            set: Default::default(),
+        }
+    }
+}
+
+/// Returns a hh:mm:ss;frame string of time for SCC format
+pub fn get_scc_time_str(time: ccx_boundary_time) -> String {
+    // Feel sorry for formatting:(
+    let frame: u8 = (((time.time_in_ms
+        - 1000 * ((time.ss as i64) + 60 * ((time.mm as i64) + 60 * (time.hh as i64))))
+        as f64)
+        * 29.97
+        / 1000.0) as u8;
+    format!("{:02}:{:02}:{:02};{:02}", time.hh, time.mm, time.ss, frame)
+}