[IMPROVEMENT]: Ensure WebVTT output includes minimal X-TIMESTAMP-MAP for HLS compatibility

[AbHash-RixE]

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SUMMARY

This PR ensures that when --timestamp-map & --out=webvtt is used and no captions are detected, CCExtractor still writes a minimal header containing : X-TIMESTAMP-MAP=MPEGTS:0,LOCAL:00:00:00.000
This makes the generated .vtt file valid for HLS players, which often require this header even in empty subtitle files.

IMPLEMENTATION DETAILS

1. CHANGES.TXT

-Added entry under Unreleased: 1.0
IMPROVEMENT: Add default X-TIMESTAMP-MAP header for empty subtitle files in WebVTT for better compatibility
of HLS streaming (#1743)

2. src/ccextractor.c

-Call webvtt_write_minimal_header() in start_ccx() when no captions are found and --out=webvtt is set.

3. src/lib_ccx/ccx_encoders_helpers.c

-Added new helper function webvtt_write_minimal_header()
-Which:
Initializes encoder context for WebVTT.
Writes a default X-TIMESTAMP-MAP=MPEGTS:0,LOCAL:00:00:00.000 line.
Ensures line terminator respects user config (LF vs CRLF).
Cleans up encoder context properly.

4. src/lib_ccx/ccx_encoders_helpers.h

-Declared the new function: void webvtt_write_minimal_header(void);

[ccextractor-bot]

CCExtractor CI platform finished running the test files on linux. Below is a summary of the test results, when compared to test for commit 3f44115...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	27/27
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	86/86
Teletext	21/21
WTV	13/13
XDS	34/34

All tests passing on the master branch were passed completely.

Check the result page for more info.

[ccextractor-bot]

CCExtractor CI platform finished running the test files on windows. Below is a summary of the test results, when compared to test for commit 3f44115...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	27/27
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	86/86
Teletext	21/21
WTV	13/13
XDS	34/34

Congratulations: Merging this PR would fix the following tests:

• ccextractor --autoprogram --out=srt --latin1 f1422b8bfe..., Last passed: Never
• ccextractor --datapid 5603 --autoprogram --out=srt --latin1 --teletext 85c7fc1ad7..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 c0d2fba8c0..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 006fdc391a..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 e92a1d4d2a..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 7e4ebf7fd7..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 9256a60e4b..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 27d7a43dd6..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 297a44921a..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 efbe129086..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 eae0077731..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 e2e2b501e0..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 c6407fb294..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 --datets dcada745de..., Last passed: Never
• ccextractor --autoprogram --out=srt --latin1 --tpage 398 5d5838bde9..., Last passed: Never
• ccextractor --autoprogram --out=srt --latin1 --teletext --tpage 398 3b276ad8bf..., Last passed: Never

All tests passing on the master branch were passed completely.

Check the result page for more info.