[FEATURE] Allow output \0 terminated frames (for WebSocket streaming support)

docs/CHANGES.TXT

@@ -1,5 +1,6 @@
 0.96.7 (unreleased)
 -------------------
+- New: Allow output \0 terminated frames via --null-terminated
 - New: Added ASS/SSA \pos-based positioning for CEA-608 captions when layout is simple (1–2 rows) (#1726)
 - 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.

src/lib_ccx/ccx_common_option.c

@@ -134,6 +134,7 @@ void init_options(struct ccx_s_options *options)
 	options->enc_cfg.trim_subs = 0; // "	Remove spaces at sides?	"
 	options->enc_cfg.in_format = 1;
 	options->enc_cfg.line_terminator_lf = 0; // 0 = CRLF
+	options->enc_cfg.frame_terminator_0 = 0; // 0 = frames terminated by line_terminator_lf
 	options->enc_cfg.start_credits_text = NULL;
 	options->enc_cfg.end_credits_text = NULL;
 	options->enc_cfg.encoding = CCX_ENC_UTF_8;

src/lib_ccx/ccx_common_option.h

@@ -67,6 +67,7 @@ struct encoder_cfg
 	int no_type_setting;
 	int cc_to_stdout;	// If this is set to 1, the stdout will be flushed when data was written to the screen during a process_608 call.
 	int line_terminator_lf; // 0 = CRLF, 1=LF
+	int frame_terminator_0; // 0 = frames terminated by line_terminator_lf, 1 = frames terminated by \0
 	LLONG subs_delay;	// ms to delay (or advance) subs
 	int program_number;
 	unsigned char in_format;

src/lib_ccx/ccx_encoders_common.c

@@ -843,6 +843,17 @@ struct encoder_ctx *init_encoder(struct encoder_cfg *opt)
 
 	ctx->encoded_br_length = encode_line(ctx, ctx->encoded_br, (unsigned char *)"<br>");
 
+	if (opt->frame_terminator_0)
+	{
+		ctx->encoded_end_frame[0] = '\0';
+		ctx->encoded_end_frame_length = 1;
+	}
+	else
+	{
+		memcpy(ctx->encoded_end_frame, ctx->encoded_crlf, ctx->encoded_crlf_length + 1);
+		ctx->encoded_end_frame_length = ctx->encoded_crlf_length;
+	}
+
 	for (i = 0; i < ctx->nb_out; i++)
 		write_subtitle_file_header(ctx, ctx->out + i);
 

src/lib_ccx/ccx_encoders_common.h

@@ -146,6 +146,8 @@ struct encoder_ctx
 	unsigned int encoded_crlf_length;
 	unsigned char encoded_br[16];
 	unsigned int encoded_br_length;
+	unsigned char encoded_end_frame[16];
+	unsigned int encoded_end_frame_length;
 
 	// MCC File
 	int header_printed_flag;

src/lib_ccx/ccx_encoders_transcript.c

@@ -92,7 +92,7 @@ int write_cc_bitmap_as_transcript(struct cc_subtitle *sub, struct encoder_ctx *c
 				}
 			}
 
-			write_wrapped(context->out->fh, context->encoded_crlf, context->encoded_crlf_length);
+			write_wrapped(context->out->fh, context->encoded_end_frame, context->encoded_end_frame_length);
 		}
 	}
 #endif
@@ -134,6 +134,7 @@ int write_cc_subtitle_as_transcript(struct cc_subtitle *sub, struct encoder_ctx
 
 		str = sub->data;
 
+		int wrote_something = 0;
 		str = strtok_r(str, "\r\n", &save_str);
 		do
 		{
@@ -143,6 +144,15 @@ int write_cc_subtitle_as_transcript(struct cc_subtitle *sub, struct encoder_ctx
 				continue;
 			}
 
+			if (wrote_something)
+			{
+				ret = write(context->out->fh, context->encoded_crlf, context->encoded_crlf_length);
+				if (ret < context->encoded_crlf_length)
+				{
+					mprint("Warning:Loss of data\n");
+				}
+			}
+
 			if (context->transcript_settings->showStartTime)
 			{
 				char buf[80];
@@ -200,14 +210,16 @@ int write_cc_subtitle_as_transcript(struct cc_subtitle *sub, struct encoder_ctx
 				mprint("Warning:Loss of data\n");
 			}
 
-			ret = write(context->out->fh, context->encoded_crlf, context->encoded_crlf_length);
-			if (ret < context->encoded_crlf_length)
-			{
-				mprint("Warning:Loss of data\n");
-			}
+			wrote_something = 1;
 
 		} while ((str = strtok_r(NULL, "\r\n", &save_str)));
 
+		ret = write(context->out->fh, context->encoded_end_frame, context->encoded_end_frame_length);
+		if (ret < context->encoded_end_frame_length)
+		{
+			mprint("Warning:Loss of data\n");
+		}
+
 		freep(&sub->data);
 		lsub = sub;
 		sub = sub->next;
@@ -321,29 +333,43 @@ void write_cc_line_as_transcript2(struct eia608_screen *data, struct encoder_ctx
 		{
 			mprint("Warning:Loss of data\n");
 		}
-
-		ret = write(context->out->fh, context->encoded_crlf, context->encoded_crlf_length);
-		if (ret < context->encoded_crlf_length)
-		{
-			mprint("Warning:Loss of data\n");
-		}
 	}
 	// fprintf (wb->fh,encoded_crlf);
 }
 
 int write_cc_buffer_as_transcript2(struct eia608_screen *data, struct encoder_ctx *context)
 {
+	int ret;
 	int wrote_something = 0;
 	dbg_print(CCX_DMT_DECODER_608, "\n- - - TRANSCRIPT caption - - -\n");
 
 	for (int i = 0; i < 15; i++)
 	{
 		if (data->row_used[i])
 		{
+			if (wrote_something)
+			{
+				ret = write(context->out->fh, context->encoded_crlf, context->encoded_crlf_length);
+				if (ret < context->encoded_crlf_length)
+				{
+					mprint("Warning:Loss of data\n");
+				}
+			}
+
 			write_cc_line_as_transcript2(data, context, i);
+			wrote_something = 1;
 		}
-		wrote_something = 1;
 	}
+
+	if (wrote_something)
+	{
+		ret = write(context->out->fh, context->encoded_end_frame, context->encoded_end_frame_length);
+		if (ret < context->encoded_end_frame_length)
+		{
+			mprint("Warning:Loss of data\n");
+		}
+	}
+
 	dbg_print(CCX_DMT_DECODER_608, "- - - - - - - - - - - -\r\n");
 	return wrote_something;
 }

src/lib_ccx/params.c

@@ -347,6 +347,9 @@ void print_usage(void)
 	mprint("                       to the output file.\n");
 	mprint("                  --lf: Use LF (UNIX) instead of CRLF (DOS, Windows) as line\n");
 	mprint("                       terminator.\n");
+	mprint("     --null-terminated: Use \\0 instead of CRLF or LF for frame termination (see '--lf').\n");
+	mprint("                       e.g use '--txt --stdout --null-terminated' when piping to\n");
+	mprint("                       'websocat -0' (https://github.com/vi/websocat)\n");
 	mprint("                  --df: For MCC Files, force dropframe frame count.\n");
 	mprint("            --autodash: Based on position on screen, attempt to determine\n");
 	mprint("                       the different speakers and a dash (-) when each\n");

src/rust/lib_ccxr/src/common/options.rs

@@ -248,6 +248,7 @@ impl Default for EncoderConfig {
             no_type_setting: false,
             cc_to_stdout: false,
             line_terminator_lf: false,
+            frame_terminator_0: false,
             subs_delay: Timestamp::default(),
             program_number: 0,
             in_format: 1,
@@ -324,6 +325,8 @@ pub struct EncoderConfig {
     pub cc_to_stdout: bool,
     /// false = CRLF, true = LF
     pub line_terminator_lf: bool,
+    /// false = frames terminated by line_terminator_lf, true = frames terminated by \0
+    pub frame_terminator_0: bool,
     /// ms to delay (or advance) subs
     pub subs_delay: Timestamp,
     pub program_number: u32,

src/rust/src/args.rs

@@ -565,6 +565,9 @@ pub struct Args {
     /// terminator.
     #[arg(long, verbatim_doc_comment, help_heading=OUTPUT_AFFECTING_OUTPUT_FILES)]
     pub lf: bool,
+    /// Use \0 instead of CRLF or LF for frame termination (see '--lf')
+    #[arg(long, verbatim_doc_comment, help_heading=OUTPUT_AFFECTING_OUTPUT_FILES)]
+    pub null_terminated: bool,
     /// For MCC Files, force dropframe frame count.
     #[arg(long, verbatim_doc_comment, help_heading=OUTPUT_AFFECTING_OUTPUT_FILES)]
     pub df: bool,

src/rust/src/common.rs

@@ -960,6 +960,7 @@ impl CType<encoder_cfg> for EncoderConfig {
             no_type_setting: self.no_type_setting as _,
             cc_to_stdout: self.cc_to_stdout as _,
             line_terminator_lf: self.line_terminator_lf as _,
+            frame_terminator_0: self.frame_terminator_0 as _,
             subs_delay: self.subs_delay.millis(),
             program_number: self.program_number as _,
             in_format: self.in_format,

src/rust/src/ctorust.rs

@@ -442,6 +442,7 @@ impl FromCType<encoder_cfg> for EncoderConfig {
             no_type_setting: cfg.no_type_setting != 0,
             cc_to_stdout: cfg.cc_to_stdout != 0,
             line_terminator_lf: cfg.line_terminator_lf != 0,
+            frame_terminator_0: cfg.frame_terminator_0 != 0,
             subs_delay: Timestamp::from_millis(cfg.subs_delay),
             program_number: cfg.program_number as u32,
             in_format: cfg.in_format,

src/rust/src/decoder/output.rs

@@ -14,7 +14,7 @@ use log::{debug, warn};
 pub struct Writer<'a> {
     pub cea_708_counter: &'a mut u32,
     pub subs_delay: LLONG,
-    pub crlf: String,
+    pub end_frame: Vec<u8>,
     pub write_format: ccx_output_format,
     pub writer_ctx: &'a mut dtvcc_writer_ctx,
     pub no_font_color: bool,
@@ -25,6 +25,7 @@ pub struct Writer<'a> {
 
 impl<'a> Writer<'a> {
     /// Create a new writer context
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         cea_708_counter: &'a mut u32,
         subs_delay: LLONG,
@@ -33,11 +34,12 @@ impl<'a> Writer<'a> {
         no_font_color: i32,
         transcript_settings: &'a ccx_encoders_transcript_format,
         no_bom: i32,
+        encoded_end_frame: &[u8],
     ) -> Self {
         Self {
             cea_708_counter,
             subs_delay,
-            crlf: "\r\n".to_owned(),
+            end_frame: encoded_end_frame.to_vec(),
             write_format,
             writer_ctx,
             no_font_color: is_true(no_font_color),

src/rust/src/decoder/service_decoder.rs

@@ -873,6 +873,7 @@ impl dtvcc_service_decoder {
             } else {
                 &ccx_encoders_transcript_format::default()
             };
+            let end_frame = &encoder.encoded_end_frame[..encoder.encoded_end_frame_length as usize];
             let mut writer = Writer::new(
                 &mut encoder.cea_708_counter,
                 encoder.subs_delay,
@@ -881,6 +882,7 @@ impl dtvcc_service_decoder {
                 encoder.no_font_color,
                 transcript_settings,
                 encoder.no_bom,
+                end_frame,
             );
             tv.writer_output(&mut writer).unwrap();
             tv.clear();
@@ -1202,6 +1204,7 @@ impl dtvcc_service_decoder {
             let sn = tv.service_number;
             let writer_ctx = &mut encoder.dtvcc_writers[(sn - 1) as usize];
 
+            let end_frame = &encoder.encoded_end_frame[..encoder.encoded_end_frame_length as usize];
             let mut writer = Writer::new(
                 &mut encoder.cea_708_counter,
                 encoder.subs_delay,
@@ -1210,6 +1213,7 @@ impl dtvcc_service_decoder {
                 encoder.no_font_color,
                 transcript_settings,
                 encoder.no_bom,
+                end_frame,
             );
             writer.write_done();
         }

src/rust/src/decoder/tv_screen.rs

@@ -330,8 +330,13 @@ impl dtvcc_tv_screen {
         let time_show = get_time_str(self.time_ms_show);
         let time_hide = get_time_str(self.time_ms_hide);
 
+        let mut wrote_something = false;
         for row_index in 0..CCX_DTVCC_SCREENGRID_ROWS as usize {
             if !self.is_row_empty(row_index) {
+                if wrote_something {
+                    writer.write_to_file(b"\r\n")?;
+                }
+
                 let mut buf = String::new();
 
                 if is_true(writer.transcript_settings.showStartTime) {
@@ -350,9 +355,11 @@ impl dtvcc_tv_screen {
                 }
                 writer.write_to_file(buf.as_bytes())?;
                 self.write_row(writer, row_index, false)?;
-                writer.write_to_file(b"\r\n")?;
+                wrote_something = true;
             }
         }
+        let end_frame = writer.end_frame.clone();
+        writer.write_to_file(&end_frame)?;
         Ok(())
     }
 
@@ -800,6 +807,7 @@ mod test {
             0,
             &transcript_settings,
             0,
+            b"\r\n",
         );
 
         // This should succeed without error (fd is valid, not -1)
@@ -835,6 +843,7 @@ mod test {
             0,
             &transcript_settings,
             0,
+            b"\r\n",
         );
 
         // This should return an error, not panic

src/rust/src/parser.rs

@@ -1257,6 +1257,10 @@ impl OptionsExt for Options {
             self.enc_cfg.line_terminator_lf = true;
         }
 
+        if args.null_terminated {
+            self.enc_cfg.frame_terminator_0 = true;
+        }
+
         if args.df {
             self.enc_cfg.force_dropframe = true;
         }