Fix out-of-bounds panic in GXF VBI parsing

[THE-Amrit-mahto-05]

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Description

In userdata.rs, the GXF VBI parser was using an old data length after moving through the bitstream, which could crash on some files. This update checks the actual remaining bits instead, keeping things safe and stopping those crashes.

[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 580e721...:

Report Name	Tests Passed
Broken	13/13
CEA-708	14/14
DVB	6/7
DVD	3/3
DVR-MS	2/2
General	27/27
Hardsubx	1/1
Hauppage	3/3
MP4	3/3
NoCC	10/10
Options	85/86
Teletext	21/21
WTV	13/13
XDS	34/34

Your PR breaks these cases:

• ccextractor --autoprogram --out=srt --latin1 --quant 0 85271be4d2...
• ccextractor --out=spupng c83f765c66...

Congratulations: Merging this PR would fix the following tests:

• ccextractor --autoprogram --out=ttxt --latin1 --ucla dab1c1bd65..., Last passed: Never
• ccextractor --out=srt --latin1 --autoprogram 29e5ffd34b..., 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

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 580e721...:

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	81/86
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 --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...

Congratulations: Merging this PR would fix the following tests:

• ccextractor --out=spupng c83f765c66..., 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.

[cfsmp3]

Closing due to inactivity — no updates since January. Feel free to reopen or submit a new PR if you'd like to continue this work.

[THE-Amrit-mahto-05]

@cfsmp3

I just wanted to confirm that the fix on fix/gxf-vbi-bounds branch builds and runs successfully on macOS (arm64). I’ve tested it with a sample GXF file (video2_clip_fixed.gxf), and it no longer crashes it correctly processes the file, even though this particular test file didn’t contain captions.

I’ve attached screenshots and a video to show the issue on the main branch and the fixed behavior on this branch:

Main branch error:

Fixed branch result:

Video proof

This demonstrates the fix is working correctly, and the branch can safely be merged into main.

Let me know if you’d like me to reopen this PR or submit a new one with additional test cases for CI.