fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering #1852

cfsmp3 · 2025-12-19T15:25:21Z

Summary

Fixes #1690 - Captions fail to extract on HEVC video stream
Fixes #1639 - CCextractor not finding 608 captions in ATSC3.0 TS (garbled output)

HEVC (H.265) video streams with embedded EIA-608/708 captions weren't being extracted correctly. VLC/MPV could display them, but CCExtractor either failed to find them or produced garbled output.

Root Causes Fixed

HEVC stream type (0x24) wasn't recognized for CC extraction in TS demuxer
HEVC NAL parsing used H.264 format (1-byte header) instead of HEVC format (2-byte header)
HEVC SEI types (39/40) weren't handled - only H.264 SEI type 6 was recognized
CC data accumulation across SEIs caused u8 overflow and garbled output
B-frame reordering not implemented for HEVC - CC data was processed in decode order instead of presentation order, scrambling character pairs

Issue #1639 Deep Dive - B-Frame Reordering

The ATSC 3.0 sample from issue #1639 exposed a critical problem: HEVC uses B-frames extensively, and CC data embedded in SEI NAL units was being processed in decode order instead of presentation order.

Evidence from the sample file:

Raw GA94 data (decode order): " BOTH OF MIOEDCRE WNDOHE TRESTH.TCL WWEILATE SEWHNSAP HPE IGAN ME..."
Correct text (presentation order): "COME BOTH OF MEDIOCRE DOWN THE STRETCH. WE WILL SEE WHAT HAPPENS IN GAME NUMBER ONE TONIGHT"

The same characters were present but scrambled due to B-frame reordering.

Before fix:

STH.TC
L  WWEILATE SEWHNSAP HPE IGAN ME

After fix:

STRETCH.
WE WILL SEE WHAT HAPPENS IN GAME
NUMBER ONE TONIGHT

Changes

C Code:

ts_info.c: Include HEVC (0x24) in video stream detection
ts_functions.c: Add CCX_HEVC buffer type handling, HEVC NAL type detection for streams without PAT/PMT (VPS=32, SPS=33, PPS=34, PREFIX_SEI=39, SUFFIX_SEI=40, IDR=19,20, CRA=21)
ccx_common_constants.h: Add CCX_HEVC = 11 buffer type
general_loop.c: Handle CCX_HEVC and set is_hevc flag
avc_functions.h: Add is_hevc field to avc_ctx

Rust Code (src/rust/src/avc/core.rs):

HEVC NAL header parsing: 2 bytes, type = (byte[0] >> 1) & 0x3F
HEVC SEI types: PREFIX_SEI (39), SUFFIX_SEI (40)
HEVC parameter sets (VPS=32, SPS=33, PPS=34) enable SEI processing

PTS-based sequence numbering for B-frame reordering (similar to H.264's pts_ordering_mode):

let pts_diff = current_pts - currefpts;
let fps_factor = MPEG_CLOCK_FREQ / current_fps;
let calculated_index = round(2.0 * pts_diff / fps_factor);

IDR-based flush - only flush CC buffer on IDR frames (NAL types 19, 20) instead of every VCL NAL, allowing proper reordering across GOP
Process and flush CC data immediately per SEI for non-B-frame content
Reset cc_count to 0 per SEI but preserve cc_data vector length

Test Results

Issue #1690 sample file - now extracts 329 lines of clean, readable captions:

1
00:00:02,620 --> 00:00:04,486
in the blink of an eye!         

2
00:00:04,488 --> 00:00:08,157
       Now that you know,       
 we can use the built-up power.

Issue #1639 sample file - garbled output now displays correctly:

STRETCH.
WE WILL SEE WHAT HAPPENS IN GAME
NUMBER ONE TONIGHT

Acknowledgments

Thanks to @trufio465-bot for the initial research direction in PR #1735. While that PR was incomplete, it helped identify the key areas that needed modification.

Test plan

Tested with sample file from issue [BUG] Captions fail to extract on HEVC video stream #1690 - captions now extract correctly
Tested with sample file from issue [BUG] CCextractor not finding 608 captions in ATSC3.0 TS #1639 - garbled captions now display correctly
CI regression tests should pass
Manual verification that existing H.264 caption extraction still works

🤖 Generated with Claude Code

@trufio465-bot

Fixes #1690 - Captions fail to extract on HEVC video stream HEVC video streams with embedded EIA-608/708 captions weren't being extracted, even though VLC/MPV could display them. Root causes fixed: 1. HEVC stream type (0x24) wasn't recognized for CC extraction 2. HEVC NAL parsing used H.264 format (1-byte) instead of HEVC (2-byte) 3. HEVC SEI types (39/40) weren't handled (only H.264 SEI type 6) 4. CC data accumulation across SEIs caused u8 overflow/garbled output Changes: - C code: Add HEVC stream detection, CCX_HEVC buffer type, is_hevc flag - Rust code: HEVC NAL header parsing (2-byte, type=(byte[0]>>1)&0x3F), HEVC SEI handling (PREFIX_SEI=39, SUFFIX_SEI=40), immediate CC flush Thanks to @trufio465-bot for the initial research in PR #1735. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

HEVC uses B-frames extensively, causing CC data to arrive in decode order instead of presentation order. This was causing character pairs to be scrambled (e.g., "MEDIOCRE" became "MIOEDCRE"). Changes: - Implement PTS-based sequence numbering for HEVC CC data (similar to H.264) - Change flush logic to only trigger on IDR frames (not every VCL NAL) - Add HEVC fallback detection for streams without PAT/PMT Fixes #1639 (ATSC 3.0 HEVC caption extraction) Tested with issue_1639_sample.ts and caption_test_1690.ts 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

The HEVC NAL type constants are defined for completeness and reference, but not all are currently used in the codebase. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

cfsmp3 · 2025-12-20T17:07:42Z

@canihavesomecoffee more samples to add

ccextractor-bot · 2025-12-20T17:13:09Z

CCExtractor CI platform finished running the test files on linux. Below is a summary of the test results, when compared to test for commit b9aabcd...:

Report Name	Tests Passed
Broken	13/13
CEA-708	9/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	24/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	81/86
Teletext	21/21
WTV	13/13
XDS	34/34

Your PR breaks these cases:

ccextractor --autoprogram --out=ttxt --latin1 1974a299f0...
ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65...
ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b...
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...

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

ccextractor --service 1 --out=txt --no-bom --no-rollup b5d6aad89f..., Last passed:
Test 6890
ccextractor --service 1[EUC-KR] --out=txt --no-rollup b5d6aad89f..., Last passed:
Test 6890
ccextractor --service 1[EUC-KR] b5d6aad89f..., Last passed:
Test 6890
ccextractor --service 1[EUC-KR] --no-rollup b5d6aad89f..., Last passed:
Test 6890
ccextractor --service all[EUC-KR] b5d6aad89f..., Last passed:
Test 6890

Congratulations: Merging this PR would fix the following tests:

ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 8e8229b88b..., Last passed: Never
ccextractor --autoprogram --out=ttxt --latin1 7236304cfc..., Last passed: Never
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ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 0069dffd21..., 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 · 2025-12-20T17:13:51Z

CCExtractor CI platform finished running the test files on windows. Below is a summary of the test results, when compared to test for commit b9aabcd...:

Report Name	Tests Passed
Broken	11/13
CEA-708	9/14
DVB	7/7
DVD	3/3
DVR-MS	2/2
General	22/27
Hardsubx	0/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	81/86
Teletext	21/21
WTV	12/13
XDS	25/34

Your PR breaks these cases:

ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 8e8229b88b...
ccextractor --out=srt --latin1 611b4a9235...
ccextractor --autoprogram --out=ttxt --latin1 132d7df7e9...
ccextractor --autoprogram --out=ttxt --latin1 99e5eaafdc...
ccextractor --autoprogram --out=ttxt --latin1 --ucla 70000200c0...
ccextractor --autoprogram --out=ttxt --latin1 --ucla 15feae9133...
ccextractor --autoprogram --out=ttxt --latin1 --ucla 95dd33c6f1...
ccextractor --hardsubx 1a0302f7fd...
ccextractor --out=dvdraw c83f765c66...
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ccextractor --endcreditsforatleast 3 --endcreditstext "CCextractor Ends crdit Testing" addf5e2fc9...
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ccextractor --out=srt --latin1 d7e7dbdf68...
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ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 27fab4dbb6...
ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds bbd5bb52fc...
ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds b992e0cccb...
ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds d0291cdcf6...
ccextractor --autoprogram --out=ttxt --latin1 --ucla 7d2730d38e...
ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 88cd42b89a...
ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 7f41299cc7...

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

ccextractor --service 1 --out=txt --no-bom --no-rollup b5d6aad89f..., Last passed:
Test 6869
ccextractor --service 1[EUC-KR] --out=txt --no-rollup b5d6aad89f..., Last passed:
Test 6869
ccextractor --service 1[EUC-KR] b5d6aad89f..., Last passed:
Test 6869
ccextractor --service 1[EUC-KR] --no-rollup b5d6aad89f..., Last passed:
Test 6869
ccextractor --service all[EUC-KR] b5d6aad89f..., Last passed:
Test 6869

Congratulations: Merging this PR would fix the following tests:

ccextractor --autoprogram --out=ttxt --latin1 7236304cfc..., Last passed: Never
ccextractor --out=sami --latin1 --autoprogram --no-goptime 5b4e0a6034..., Last passed: Never
ccextractor --service 1 --out=txt --no-bom --no-rollup ea83ff7bcb..., Last passed: Never
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ccextractor --autoprogram --out=srt --latin1 --ucla 7d3f25c32c..., 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.

shirt-dev · 2025-12-21T01:39:27Z

Looks like this now works with MPEG-TS, but I still encounter failures with MP4 and Matroska.

MP4 sample: https://drive.google.com/file/d/10X8R95TUnFzAZZkP_M2letRJzvz9OPSm/view?usp=sharing
MKV sample: https://drive.google.com/file/d/1w36ic-gbLAc6_fjMB5TDpBV8Pcs40bGC/view?usp=sharing

PR #1852 added HEVC caption extraction for MPEG-TS containers, but MP4/MKV containers weren't supported. This adds HEVC support for MP4 containers using GPAC. Changes: - Add HEVC subtype definitions (hev1, hvc1) - Add process_hevc_sample() to parse HEVC NAL units and extract CC - Add process_hevc_track() to iterate through HEVC track samples - Detect and process HEVC tracks in processmp4() - Add store_hdcc() call to flush buffered CC data after each sample The key fix was adding store_hdcc() after processing each sample. Without this, CC data was being parsed but never output because store_hdcc() is normally called from slice_header() which is AVC-only. Also includes plans/HEVC_MKV.md documenting the implementation plan for Matroska container HEVC support (not yet implemented). Closes #1690 (for MP4 containers) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

PR #1852 added HEVC caption extraction for MPEG-TS containers, but MP4/MKV containers weren't supported. This adds HEVC support for MP4 containers using GPAC. Changes: - Add HEVC subtype definitions (hev1, hvc1) - Add process_hevc_sample() to parse HEVC NAL units and extract CC - Add process_hevc_track() to iterate through HEVC track samples - Detect and process HEVC tracks in processmp4() - Add store_hdcc() call to flush buffered CC data after each sample The key fix was adding store_hdcc() after processing each sample. Without this, CC data was being parsed but never output because store_hdcc() is normally called from slice_header() which is AVC-only. Closes #1690 (for MP4 containers) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

cfsmp3 mentioned this pull request Dec 19, 2025

[FIX ]Captions fail to extract on HEVC video stream #1690 #1735

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cfsmp3 force-pushed the fix/issue-1690-hevc-caption-extraction branch from 87fbb5b to cbb1456 Compare December 19, 2025 15:47

cfsmp3 changed the title ~~fix(hevc): Add HEVC/H.265 caption extraction support~~ fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering Dec 20, 2025

cfsmp3 and others added 4 commits December 20, 2025 10:34

style: Fix clang-format issue in ts_functions.c

87bc1d9

🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

style: Run cargo fmt on avc/core.rs

9e970fd

🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <[email protected]>

cfsmp3 force-pushed the fix/issue-1690-hevc-caption-extraction branch from 4e1044e to 9e970fd Compare December 20, 2025 09:35

cfsmp3 merged commit 54bc97a into master Dec 20, 2025
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cfsmp3 deleted the fix/issue-1690-hevc-caption-extraction branch December 20, 2025 17:18

cfsmp3 mentioned this pull request Dec 21, 2025

[BUG] Captions fail to extract on HEVC video stream #1690

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fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering #1852

fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering #1852

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cfsmp3 commented Dec 19, 2025 •

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fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering #1852

fix(hevc): Add HEVC/H.265 caption extraction support with B-frame reordering #1852

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cfsmp3 commented Dec 19, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Summary

Root Causes Fixed

Issue #1639 Deep Dive - B-Frame Reordering

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cfsmp3 commented Dec 19, 2025 •

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