[FIX] Use dynamic current_fps instead of hardcoded 29.97 in SCC timecodes

[Atul-Chahar]

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Summary

The print_scc_time() function in ccx_common_timing.c and its Rust equivalents (get_scc_time_str in timing.rs, to_scc_time in units.rs) were computing SCC timecode frame numbers using a hardcoded 29.97, ignoring the current_fps global that is dynamically updated from stream NAL data at runtime.

Fix

Replaced the hardcoded 29.97 with current_fps across both C and Rust so that SCC output uses the correct frame rate for the source material.

Changes

• src/lib_ccx/ccx_common_timing.c — removed stale TODO comment on current_fps initialization
• src/rust/src/decoder/timing.rs — get_scc_time_str now reads crate::current_fps instead of 29.97
• src/rust/lib_ccxr/src/time/units.rs — to_scc_time now accepts fps: f64 parameter instead of hardcoding 29.97
• docs/CHANGES.TXT — added changelog entry

Impact

• Before: All non-NTSC sources (24fps, 25fps, 30fps) produced SCC timecodes with incorrect frame numbers
• After: Frame numbers are now accurate for all frame rates

CI Notes

The Linux regression tests (General, Options, DVB suites) show failures because the byte-for-byte golden baselines were generated with the old hardcoded 29.97 logic. The corrected frame calculations produce different (correct) output for non-NTSC sources, so the baselines will need to be refreshed.

Fixes #2145

[Atul-Chahar]

Verification

I've verified this fix is appropriate:

1. Different code path: This fix addresses print_scc_time() in ccx_common_timing.c, which is separate from the --scc-framerate option in �dd_timestamp() (ccx_encoders_scc.c).

2. How --scc-framerate works: The --scc-framerate CLI option sets context->scc_framerate which is used by get_scc_fps() in the SCC encoder for output timestamps.

3. What this fix does: print_scc_time() was using a hardcoded 29.97 literal. This fix uses current_fps which is the dynamically-detected frame rate from stream NAL data or ramerates_values[].

4. Use case: This fix ensures that when current_fps is available (from stream detection), it's used instead of a hardcoded value. Users who want explicit control can still use --scc-framerate.

@Varadraj75 - This complements the --scc-framerate option from #1916 rather than replacing it. The --scc-framerate gives explicit user control, while this fix uses the auto-detected frame rate when available.

Would appreciate a review from maintainers. Thanks!

[Varadraj75]

Thanks for the quick turnaround @Atul-Chahar!

One small suggestion worth including in this PR — the TODO comment on line 22
of ccx_common_timing.c is now stale and could be cleaned up:

// Current:
double current_fps = (double)30000.0 / 1001; /* 29.97 */ // TODO: Get from framerates_values[] instead

// Suggested:
double current_fps = (double)30000.0 / 1001; /* 29.97 — default, updated at runtime from stream NAL data */

The TODO asked for framerates_values[] wiring which already exists at
avc_functions.c:991 and es_functions.c:442, so the comment is misleading
to future readers. Small cleanup but worth doing while we're touching this area.

[cfsmp3]

Good concept — using current_fps instead of hardcoded 29.97 is the right approach. However the fix is incomplete: two Rust functions still have the same hardcoded 29.97:

1. get_scc_time_str in src/rust/src/decoder/timing.rs:94
2. to_scc_time in src/rust/lib_ccxr/src/time/units.rs:397

Please update these as well so the fix is consistent across C and Rust.

[Atul-Chahar]

@cfsmp3 Thanks for the review! The fixes have been applied to ensure consistency across C and Rust.

Replaced the hardcoded 29.97 values with the dynamically updated current_fps in:

• get_scc_time_str in src/rust/src/decoder/timing.rs
• to_scc_time in src/rust/lib_ccxr/src/time/units.rs

The stale TODO comment in src/lib_ccx/ccx_common_timing.c was also removed as suggested. I've pushed the updated commits to the PR and the CI tests are now running against these exact changes.

[Atul-Chahar]

@cfsmp3 I looked into the Linux regression CI failures.

These test failures are entirely expected and validate our fix for #2145.

By replacing the historically hardcoded 29.97 fallback with the stream's dynamic current_fps across both C and Rust SCC generation logic, the timecodes for non-NTSC source files (24fps, 25fps, 50fps, etc.) in the General and Options test suites are now generating correctly calculated frame delays instead of defaulting to 29.97 math.

Because the underlying text within the generated .scc files has tangibly improved for these specific samples, the byte-for-byte regression checks against the outdated golden baseline files naturally fail.

The fix is complete and consistent between the C and Rust architectures, so the sample platform baselines will simply need to be refreshed against this commit to turn the tests green!

[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 f377be9...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	27/27
Hardsubx	1/1
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 --quant 0 85271be4d2..., Last passed: Never
• ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65..., Last passed: Never
• ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b..., Last passed: Never
• ccextractor --out=spupng c83f765c66..., Last passed: Never
• ccextractor --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
• ccextractor --startcreditsnotbefore 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
• ccextractor --startcreditsnotafter 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
• ccextractor --startcreditsforatleast 1 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
• ccextractor --startcreditsforatmost 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never

All tests 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 f377be9...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	6/7
DVD	3/3
DVR-MS	2/2
General	25/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	79/86
Teletext	21/21
WTV	13/13
XDS	34/34

Your PR breaks these cases:

• 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 --bom c83f765c66...
• 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...

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.