feat(wtv): Add DVB teletext stream detection in WTV files

This commit adds detection and basic handling of DVB teletext streams
in WTV (Windows TV) files. Previously, teletext streams were silently
ignored.

Changes:
- Add WTV_STREAM_TELETEXT GUID to wtv_constants.h
- Detect teletext streams by examining the format GUID at offset 0x4C
  in MSTVCAPTION stream metadata
- Initialize teletext decoder when teletext stream is found
- Add timing support for teletext streams
- Wrap teletext data in PES headers for the teletext decoder

Limitation: WTV files store teletext in Microsoft's VBI sample format,
which differs from standard DVB teletext data units. The decoder will
process the data but may not extract subtitles from all WTV files.
This is noted in a warning message shown when teletext is detected.
Even FFmpeg's libzvbi fails to decode this format in the test sample.

Addresses: #1391

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: cfsmp3

src/lib_ccx/wtv_constants.h

@@ -6,6 +6,8 @@
 #define WTV_STREAM_VIDEO "\x76\x69\x64\x73\x00\x00\x10\x00\x80\x00\x00\xAA\x00\x38\x9B\x71"
 #define WTV_STREAM_AUDIO "\x61\x75\x64\x73\x00\x00\x10\x00\x80\x00\x00\xAA\x00\x38\x9B\x71"
 #define WTV_STREAM_MSTVCAPTION "\x89\x8A\x8B\xB8\x49\xB0\x80\x4C\xAD\xCF\x58\x98\x98\x5E\x22\xC1"
+// DVB Teletext stream type (VBI teletext data in PES format)
+#define WTV_STREAM_TELETEXT "\xE3\x76\x2A\xF7\x0A\xEB\xD0\x11\xAC\xE4\x00\x00\xC0\xCC\x16\xBA"
 #define WTV_EOF "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
 #define WTV_TIMING "\x5B\x05\xE6\x1B\x97\xA9\x49\x43\x88\x17\x1A\x65\x5A\x29\x8A\x97"
 

src/lib_ccx/wtv_functions.c

@@ -36,6 +36,16 @@ int check_stream_id(int stream_id, int video_streams[], int num_streams)
 	return 0;
 }
 
+// Check if the passed stream_id is a teletext stream
+int check_teletext_stream_id(int stream_id, int teletext_streams[], int num_teletext_streams)
+{
+	int x;
+	for (x = 0; x < num_teletext_streams; x++)
+		if (teletext_streams[x] == stream_id)
+			return 1;
+	return 0;
+}
+
 // Init passes wtv_chunked_buffer struct
 void init_chunked_buffer(struct wtv_chunked_buffer *cb)
 {
@@ -335,9 +345,12 @@ int read_header(struct ccx_demuxer *ctx, struct wtv_chunked_buffer *cb)
 LLONG get_data(struct lib_ccx_ctx *ctx, struct wtv_chunked_buffer *cb, struct demuxer_data *data)
 {
 	static int video_streams[32];
+	static int teletext_streams[32];
 	static int alt_stream; // Stream to use for timestamps if the cc stream has broken timestamps
 	static int use_alt_stream = 0;
 	static int num_streams = 0;
+	static int num_teletext_streams = 0;
+	static int has_teletext = 0; // Flag to indicate we found teletext streams
 	int64_t result;
 	struct lib_cc_decode *dec_ctx = update_decoder_list(ctx);
 
@@ -403,12 +416,18 @@ LLONG get_data(struct lib_ccx_ctx *ctx, struct wtv_chunked_buffer *cb, struct de
 		{
 			// The WTV_STREAM2 GUID appears near the start of the data dir
 			// It maps stream_ids to the type of stream
+			// Structure based on WTV file analysis:
+			// Offset 0x0C: mediatype GUID (16 bytes)
+			// Offset 0x4C: teletext format GUID (16 bytes) - for MSTVCAPTION streams
+			// We read enough data (96 bytes) to get all the info we need
 			dbg_print(CCX_DMT_PARSE, "WTV STREAM2\n");
-			get_sized_buffer(ctx->demux_ctx, cb, 0xc + 16);
+			// Read 96 bytes to get mediatype at 0x0C and format_subtype at 0x4C
+			uint32_t read_size = (len > 96) ? 96 : len;
+			get_sized_buffer(ctx->demux_ctx, cb, read_size);
 			if (cb->buffer == NULL)
 				return CCX_EOF;
 			static unsigned char stream_type[16];
-			memcpy(&stream_type, cb->buffer + 0xc, 16); // Read the stream type GUID
+			memcpy(&stream_type, cb->buffer + 0xc, 16); // Read the mediatype GUID at offset 12
 			const void *stream_guid;
 			if (ccx_options.wtvmpeg2)
 				stream_guid = WTV_STREAM_VIDEO; // We want mpeg2 data if the user set -wtvmpeg2
@@ -419,11 +438,40 @@ LLONG get_data(struct lib_ccx_ctx *ctx, struct wtv_chunked_buffer *cb, struct de
 				video_streams[num_streams] = stream_id; // We keep a list of stream ids
 				num_streams++;				// Even though there should only be 1
 			}
+			// For MSTVCAPTION streams, check if it's teletext by examining the format GUID
+			// The teletext GUID appears at offset 0x4C from the start of the chunk data
+			if (!memcmp(stream_type, WTV_STREAM_MSTVCAPTION, 16) && read_size >= 0x4C + 16)
+			{
+				static unsigned char format_subtype[16];
+				memcpy(&format_subtype, cb->buffer + 0x4C, 16); // Read format GUID at offset 0x4C
+				dbg_print(CCX_DMT_PARSE, "MSTVCAPTION format_subtype=%02X%02X%02X%02X...\n",
+					format_subtype[0], format_subtype[1], format_subtype[2], format_subtype[3]);
+				// Check for teletext
+				if (!memcmp(format_subtype, WTV_STREAM_TELETEXT, 16))
+				{
+					dbg_print(CCX_DMT_PARSE, "Found DVB Teletext stream, stream_id: 0x%X\n", stream_id);
+					mprint("WTV: Found DVB Teletext stream (stream_id=0x%X)\n", stream_id);
+					mprint("     Note: WTV teletext uses Microsoft VBI format which may not decode correctly.\n");
+					teletext_streams[num_teletext_streams] = stream_id;
+					num_teletext_streams++;
+					has_teletext = 1;
+					// Initialize teletext decoder context
+					if (!dec_ctx->private_data)
+					{
+						dec_ctx->codec = CCX_CODEC_TELETEXT;
+						dec_ctx->private_data = telxcc_init();
+						if (!dec_ctx->private_data)
+						{
+							mprint("Error: Failed to initialize teletext decoder\n");
+						}
+					}
+				}
+			}
 			if (memcmp(stream_type, WTV_STREAM_AUDIO, 16))
 				alt_stream = stream_id;
-			len -= 28;
+			len -= read_size;
 		}
-		if (!memcmp(guid, WTV_TIMING, 16) && ((use_alt_stream < WTV_CC_TIMESTAMP_MAGIC_THRESH && check_stream_id(stream_id, video_streams, num_streams)) || (use_alt_stream == WTV_CC_TIMESTAMP_MAGIC_THRESH && stream_id == alt_stream)))
+		if (!memcmp(guid, WTV_TIMING, 16) && ((use_alt_stream < WTV_CC_TIMESTAMP_MAGIC_THRESH && (check_stream_id(stream_id, video_streams, num_streams) || check_teletext_stream_id(stream_id, teletext_streams, num_teletext_streams))) || (use_alt_stream == WTV_CC_TIMESTAMP_MAGIC_THRESH && stream_id == alt_stream)))
 		{
 			int64_t time;
 			// The WTV_TIMING GUID contains a timestamp for the given stream_id
@@ -478,6 +526,54 @@ LLONG get_data(struct lib_ccx_ctx *ctx, struct wtv_chunked_buffer *cb, struct de
 			}
 			return bytesread;
 		}
+		// Handle DVB Teletext data
+		// Note: WTV teletext format is Microsoft-specific and differs from DVB teletext.
+		// The data is not in standard DVB teletext data unit format, so decoding support
+		// is currently limited. The stream is detected and passed to the decoder which
+		// will process what it can parse.
+		if (!memcmp(guid, WTV_DATA, 16) && check_teletext_stream_id(stream_id, teletext_streams, num_teletext_streams) && dec_ctx->timing->current_pts != 0)
+		{
+			get_sized_buffer(ctx->demux_ctx, cb, len);
+			if (cb->buffer == NULL)
+				return CCX_EOF;
+
+			// WTV teletext data is raw VBI data, not PES-encapsulated.
+			// Wrap it in a PES header for the teletext decoder.
+			uint16_t pes_len = len + 8; // payload + header fields after length
+			int64_t pts = dec_ctx->timing->current_pts;
+
+			// Add PES header (14 bytes)
+			data->buffer[data->len++] = 0x00; // start code
+			data->buffer[data->len++] = 0x00;
+			data->buffer[data->len++] = 0x01;
+			data->buffer[data->len++] = 0xBD; // Private Stream 1
+			data->buffer[data->len++] = (pes_len >> 8) & 0xFF;
+			data->buffer[data->len++] = pes_len & 0xFF;
+			data->buffer[data->len++] = 0x80; // PES flags
+			data->buffer[data->len++] = 0x80; // PTS present
+			data->buffer[data->len++] = 0x05; // header data length
+
+			// Encode PTS (33-bit value in 5 bytes)
+			data->buffer[data->len++] = (uint8_t)(0x21 | ((pts >> 29) & 0x0E));
+			data->buffer[data->len++] = (uint8_t)((pts >> 22) & 0xFF);
+			data->buffer[data->len++] = (uint8_t)(0x01 | ((pts >> 14) & 0xFE));
+			data->buffer[data->len++] = (uint8_t)((pts >> 7) & 0xFF);
+			data->buffer[data->len++] = (uint8_t)(0x01 | ((pts << 1) & 0xFE));
+
+			// Add teletext data
+			memcpy(data->buffer + data->len, cb->buffer, len);
+			data->len += len;
+			bytesread += (int)(14 + len);
+			data->codec = CCX_CODEC_TELETEXT;
+			data->bufferdatatype = CCX_TELETEXT;
+			frames_since_ref_time++;
+			set_fts(dec_ctx->timing);
+			if (pad > 0)
+			{
+				skip_sized_buffer(ctx->demux_ctx, cb, pad);
+			}
+			return bytesread;
+		}
 		if (len + pad > 0)
 		{
 			// skip any remaining data