[FIX] transcript: suppress spurious blank lines from write_cc_line_as_transcript2

[x15sr71]

In raising this pull request, I confirm the following (please check boxes):

Reason for this PR:

• This PR adds new functionality.
• This PR fixes a bug that I have personally experienced or that a real user has reported and for which a sample exists.
• This PR is porting code from C to Rust.

Sanity check:

• I have read and understood the contributors guide.
• I have checked that another pull request for this purpose does not exist.
• If the PR adds new functionality, I've added it to the changelog. If it's just a bug fix, I have NOT added it to the changelog.
• I am NOT adding new C code unless it's to fix an existing, reproducible bug.

Repro instructions:

Run with --autoprogram --out=ttxt --latin1 on any sample with a pop-on → roll-up mode transition. The output contains one or more spurious blank lines not present in the reference file. Confirmed on the sample platform via RT41, RT84, RT11, RT29, RT30.

---

Issue:

write_cc_buffer_as_transcript2 emits spurious blank lines in --out=ttxt output on samples with pop-on → roll-up transitions.

Root cause:

Introduced in PR #2105 - it refactored write_cc_buffer_as_transcript2 to emit encoded_end_frame after each block, and changed the call to:

write_cc_line_as_transcript2(data, context, i);
wrote_something = 1;   // unconditional

Because write_cc_line_as_transcript2 returned void, the caller couldn't know it wrote nothing (blank cursor row). wrote_something got set to 1 anyway, so a bare newline was emitted for every empty row.

Fix:

Change write_cc_line_as_transcript2 from void to int (returns 1 if content was written, 0 if not) and use |= in the caller:
wrote_something |= write_cc_line_as_transcript2(data, context, i); encoded_end_frame is now only written when at least one line produced output.

Testing:

• RT41 (01509...ts, --out=ttxt --latin1): two spurious blank lines removed. Output is byte-identical to accepted variant ref 9f139b8c...

[x15sr71]

The Docker build (hardsubx) failure is unrelated to this PR — it's a transient Docker Hub auth outage (500 Internal Server Error on auth.docker.io/token). The other two Docker jobs passed in the same run. A re-run should clear it.

[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 128175e...:

Report Name	Tests Passed
Broken	9/13
CEA-708	2/14
DVB	1/7
DVD	3/3
DVR-MS	2/2
General	25/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	69/86
Teletext	0/21
WTV	12/13
XDS	32/34

Your PR breaks these cases:

• ccextractor --out=srt --latin1 611b4a9235...
• ccextractor --autoprogram --out=ttxt --latin1 1020459a86...
• ccextractor --datapid 5603 --autoprogram --out=srt --latin1 --teletext 85c7fc1ad7...
• ccextractor --autoprogram --out=srt --latin1 --quant 0 85271be4d2...
• ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65...
• ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b...
• ccextractor --out=spupng c83f765c66...
• ccextractor --dru c83f765c66...
• ccextractor --startat 4 --endat 7 c83f765c66...
• ccextractor --codec dvbsub --out=spupng 85271be4d2...
• ccextractor --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotbefore 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsnotafter 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatleast 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --startcreditsforatmost 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9...
• ccextractor --tpage 801 4e56e88ba4...
• ccextractor --tverbose 4e56e88ba4...
• ccextractor --teletext 4e56e88ba4...
• ccextractor --autoprogram --out=srt --latin1 4e56e88ba4...
• ccextractor --autoprogram --out=ttxt --latin1 c0d2fba8c0...
• ccextractor --autoprogram --out=ttxt --latin1 006fdc391a...
• ccextractor --autoprogram --out=ttxt --latin1 e92a1d4d2a...
• ccextractor --autoprogram --out=ttxt --latin1 b37ce60eb9...
• ccextractor --autoprogram --out=ttxt --latin1 7e4ebf7fd7...
• ccextractor --autoprogram --out=ttxt --latin1 9256a60e4b...
• ccextractor --autoprogram --out=ttxt --latin1 27d7a43dd6...
• ccextractor --autoprogram --out=ttxt --latin1 297a44921a...
• ccextractor --autoprogram --out=ttxt --latin1 efbe129086...
• ccextractor --autoprogram --out=ttxt --latin1 eae0077731...
• ccextractor --autoprogram --out=ttxt --latin1 e2e2b501e0...
• ccextractor --autoprogram --out=ttxt --latin1 8c1615c1a8...
• ccextractor --autoprogram --out=ttxt --latin1 c6407fb294...
• ccextractor --autoprogram --out=ttxt --latin1 --datets dcada745de...
• ccextractor --autoprogram --out=srt --latin1 --tpage 398 5d5838bde9...
• ccextractor --autoprogram --out=srt --latin1 --tpage 299 44c45593fb...
• ccextractor --autoprogram --out=srt --latin1 --tpage 299 b8c55aa2e9...
• ccextractor --autoprogram --out=srt --latin1 --teletext --tpage 398 3b276ad8bf...
• ccextractor --autoprogram --out=ttxt --latin1 b236a0590b...
• ccextractor --out=srt --latin1 f23a544ba8...
• ccextractor --autoprogram --out=srt --latin1 --ucla d037c7509e...
• ccextractor --autoprogram --out=srt --latin1 --ucla 7d3f25c32c...

NOTE: The following tests have been failing on the master branch as well as the PR:

• ccextractor --out=srt --latin1 --autoprogram 73d9313d64..., Last passed:

  Test 8738

• ccextractor --out=ttxt --latin1 001dd8cdf7..., Last passed:

  Test 8738

• ccextractor --out=srt --latin1 4d4e938ef6..., Last passed:

  Test 8738

• ccextractor --service 1 --out=txt --no-bom --no-rollup ea83ff7bcb..., Last passed:

  Test 8738

• ccextractor --service 1 --out=txt f17524b53f..., Last passed:

  Test 8738

• ccextractor --service 1 --out=txt 80848c45f8..., Last passed:

  Test 8738

• ccextractor --service 1 --out=txt --no-bom --no-rollup b5d6aad89f..., Last passed:

  Test 8738

• ccextractor --service 1[EUC-KR] --out=txt --no-rollup b5d6aad89f..., Last passed:

  Test 8738

• ccextractor --service 1 --out=srt da904de35d..., Last passed:

  Test 8738

• ccextractor --service 1 --out=sami da904de35d..., Last passed:

  Test 8738

• ccextractor --service 1[EUC-KR] b5d6aad89f..., Last passed:

  Test 8738

• ccextractor --service 1[EUC-KR] --no-rollup b5d6aad89f..., Last passed:

  Test 8738

• ccextractor --service all da904de35d..., Last passed:

  Test 8738

• ccextractor --service all[EUC-KR] b5d6aad89f..., Last passed:

  Test 8738

• ccextractor --service 1,2[UTF-8],3[EUC-KR],54 --out=txt da904de35d..., Last passed:

  Test 8738

• ccextractor --autoprogram --out=srt --latin1 d41b53b504..., Last passed:

  Test 8738

• ccextractor --stdout --quiet --no-fontcolor 79a51f3500..., Last passed:

  Test 8738

• ccextractor --stdout --quiet --no-fontcolor 767b546f96..., Last passed:

  Test 8738

• ccextractor --service 1 c83f765c66..., Last passed:

  Test 8738

• ccextractor --myth c83f765c66..., Last passed:

  Test 8738

• ccextractor --in=raw fb79021542..., Last passed:

  Test 8738

• ccextractor --mp4vidtrack 5df914ce77..., Last passed:

  Test 8738

• ccextractor --xmltv=3 --out=null 96efd279cf..., Last passed:

  Test 8738

• ccextractor --datapid 2310 --autoprogram --out=srt --latin1 e639e54550..., Last passed:

  Test 8738

Congratulations: Merging this PR would fix the following tests:

• ccextractor --autoprogram --out=srt --latin1 f1422b8bfe..., Last passed: Never

It seems that not all tests were passed completely. This is an indication that the output of some files is not as expected (but might be according to you).

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 128175e...:

Report Name	Tests Passed
Broken	10/13
CEA-708	2/14
DVB	3/7
DVD	3/3
DVR-MS	2/2
General	27/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	81/86
Teletext	20/21
WTV	13/13
XDS	34/34

NOTE: The following tests have been failing on the master branch as well as the PR:

• ccextractor --out=srt --latin1 --autoprogram 73d9313d64..., Last passed:

  Test 8611

• ccextractor --out=ttxt --latin1 001dd8cdf7..., Last passed:

  Test 8611

• ccextractor --out=srt --latin1 4d4e938ef6..., Last passed:

  Test 8611

• ccextractor --service 1 --out=txt --no-bom --no-rollup ea83ff7bcb..., Last passed:

  Test 8611

• ccextractor --service 1 --out=txt f17524b53f..., Last passed:

  Test 8611

• ccextractor --service 1 --out=txt 80848c45f8..., Last passed:

  Test 8611

• ccextractor --service 1 --out=txt --no-bom --no-rollup b5d6aad89f..., Last passed:

  Test 8611

• ccextractor --service 1[EUC-KR] --out=txt --no-rollup b5d6aad89f..., Last passed:

  Test 8611

• ccextractor --service 1 --out=srt da904de35d..., Last passed:

  Test 8611

• ccextractor --service 1 --out=sami da904de35d..., Last passed:

  Test 8611

• ccextractor --service 1[EUC-KR] b5d6aad89f..., Last passed:

  Test 8611

• ccextractor --service 1[EUC-KR] --no-rollup b5d6aad89f..., Last passed:

  Test 8611

• ccextractor --service all da904de35d..., Last passed:

  Test 8611

• ccextractor --service all[EUC-KR] b5d6aad89f..., Last passed:

  Test 8611

• ccextractor --service 1,2[UTF-8],3[EUC-KR],54 --out=txt da904de35d..., Last passed:

  Test 8611

• ccextractor --autoprogram --out=srt --latin1 f1422b8bfe..., Last passed:

  Test 9209

• ccextractor --autoprogram --out=srt --latin1 d41b53b504..., Last passed:

  Test 8611

• ccextractor --stdout --quiet --no-fontcolor 79a51f3500..., Last passed:

  Test 8611

• ccextractor --stdout --quiet --no-fontcolor 767b546f96..., Last passed:

  Test 8611

• ccextractor --service 1 c83f765c66..., Last passed:

  Test 8611

• ccextractor --myth c83f765c66..., Last passed:

  Test 8611

• ccextractor --in=raw fb79021542..., Last passed:

  Test 8611

• ccextractor --mp4vidtrack 5df914ce77..., Last passed:

  Test 8611

• ccextractor --xmltv=3 --out=null 96efd279cf..., Last passed:

  Test 8611

• ccextractor --datapid 2310 --autoprogram --out=srt --latin1 e639e54550..., Last passed:

  Test 8611

This PR does not introduce any new test failures. However, some tests are failing on both master and this PR (see above).

Check the result page for more info.