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fix: prevent infinite loop when processing TS files with no subtitles #1763

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fix: prevent infinite loop when processing TS files with no subtitles #1763

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@DhanushVarma-2
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@DhanushVarma-2 DhanushVarma-2 commented Nov 10, 2025 •
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Problem
When processing TS files containing no subtitles, ccextractor enters an infinite loop instead of exiting gracefully (Issue #1754).

Root Cause
The ts_readstream function had a do-while (!gotpes) loop that would run indefinitely when no subtitle streams were detected, because gotpes never became true in files without subtitles.

Solution
Instead of using an arbitrary packet limit, this fix properly detects when no subtitle streams exist by:

  1. Tracking PMT analysis: Monitors when all Program Map Tables have been analyzed
  2. Checking for caption streams: After PMT analysis, checks if any caption PIDs were registered (ctx->num_of_PIDs == 0)
  3. Grace period: Waits 1000 packets after PMT analysis to ensure all streams are detected
  4. Clean exit: Returns CCX_EOF with a clear debug message when no subtitles are found

Why This Approach is Better

  • PMT-based detection: Uses actual stream metadata instead of arbitrary limits
  • Deterministic: Based on MPEG-TS structure, not guesswork
  • Faster: Exits as soon as it's confirmed no caption streams exist (~1000 packets vs 50,000)
  • Maintains compatibility: Works for files with subtitles exactly as before
  • No magic numbers: Logic is based on actual stream parsing

Changes Made

  • src/lib_ccx/ts_functions.c: Added PMT analysis tracking and caption stream detection in ts_readstream function

Testing

  • Code compiles successfully without errors
  • Maintains backward compatibility for files with subtitles

Fixes #1754

@cfsmp3
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cfsmp3 commented Dec 8, 2025

Why would no subtitles cause an infinite loop? Do you have an example file?

I don't like the heuristics solution TBH.

@cfsmp3 cfsmp3 self-requested a review December 8, 2025 02:04
cfsmp3
cfsmp3 requested changes Dec 8, 2025
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Please submit an example video to shows the problem.
There must be a way to fix it that doesn't consist on a random limit.

@DhanushVarma-2
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DhanushVarma-2 commented Dec 8, 2025

Example TS file (no subtitles):
no_subs.ts
This is a valid MPEG-TS containing video + audio only, with no subtitle streams
Verified via:
ffprobe no_subs.ts | grep -i subtitle
(no output)

@DhanushVarma-2
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DhanushVarma-2 commented Dec 8, 2025

A hard packet limit is not ideal and was added only as a safeguard to prevent the infinite loop.
The fix can instead terminate cleanly based on EOF / PMT parsing when no subtitle streams exist

@DhanushVarma-2 DhanushVarma-2 requested a review from cfsmp3 December 8, 2025 07:23
fix: prevent infinite loop when TS files have no subtitle streams
8d4d84b 
- Check if all PMTs have been analyzed
- After PMT analysis, verify if any caption streams (PIDs) were found
- Exit after 1000 packets if num_of_PIDs == 0 (no caption streams)
- Uses PMT-based detection instead of arbitrary packet limits

This fix properly uses the Program Map Table data to determine if
subtitle streams exist, rather than relying on arbitrary packet counts.

Fixes CCExtractor#1754
@DhanushVarma-2 DhanushVarma-2 force-pushed the fix-ts-infinite-loop-fresh branch from 8e5f4d2 to 8d4d84b Compare December 17, 2025 06:53
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ccextractor-bot commented Dec 17, 2025

CCExtractor CI platform finished running the test files on linux. Below is a summary of the test results, when compared to test for commit 0b3ad40...:
Report Name Tests Passed
Broken 3/13
CEA-708 13/14
DVB 4/7
DVD 0/3
DVR-MS 2/2
General 5/27
Hardsubx 0/1
Hauppage 0/3
MP4 3/3
NoCC 10/10
Options 62/86
Teletext 1/21
WTV 0/13
XDS 25/34

Your PR breaks these cases:

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


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.

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ccextractor-bot commented Dec 17, 2025

CCExtractor CI platform finished running the test files on windows. Below is a summary of the test results, when compared to test for commit f6cb862...:
Report Name Tests Passed
Broken 12/13
CEA-708 14/14
DVB 5/7
DVD 3/3
DVR-MS 2/2
General 27/27
Hardsubx 0/1
Hauppage 3/3
MP4 3/3
NoCC 10/10
Options 75/86
Teletext 1/21
WTV 13/13
XDS 34/34

Your PR breaks these cases:

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

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 --out=sami --latin1 --autoprogram --no-goptime 5b4e0a6034..., Last passed: Never
  • ccextractor --service 1 --out=ttxt da904de35d..., Last passed: Never
  • ccextractor --autoprogram --out=srt --latin1 --quant 0 85271be4d2..., Last passed: Never
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  • ccextractor --autoprogram --out=ttxt --latin1 --ucla 7aad20907e..., Last passed: Never
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  • ccextractor --autoprogram --out=srt --latin1 --sentencecap c032183ef0..., Last passed: Never
  • ccextractor --autoprogram --out=bin --latin1 c032183ef0..., Last passed: Never
  • ccextractor --hauppauge --autoprogram --out=srt --latin1 a03b5b2a56..., Last passed: Never
  • ccextractor --autoprogram --out=srt --hauppauge --latin1 553d78e755..., Last passed: Never
  • ccextractor --autoprogram --out=ttxt --hauppauge --ucla --latin1 553d78e755..., Last passed: Never
  • ccextractor --out=ttxt c83f765c66..., Last passed: Never
  • ccextractor --goptime c83f765c66..., Last passed: Never
  • ccextractor --in=es dc7169d7c4..., Last passed: Never
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  • ccextractor --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
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  • ccextractor --startcreditsforatmost 2 --startcreditstext "CCextractor Start crdit Testing" c4dd893cb9..., Last passed: Never
  • ccextractor --endcreditstext "CCextractor Ends crdit Testing" addf5e2fc9..., Last passed: Never
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  • ccextractor --endcreditsforatmost 2 --endcreditstext "CCextractor Ends crdit Testing" addf5e2fc9..., Last passed: Never
  • ccextractor --autoprogram --out=ttxt --latin1 --datets dcada745de..., Last passed: Never
  • ccextractor --out=srt --latin1 f23a544ba8..., Last passed: Never
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  • ccextractor --autoprogram --out=ttxt --latin1 --ucla --xds 725a49f871..., Last passed: Never
  • ccextractor --autoprogram --out=ttxt --latin1 --xds --ucla c813e713a0..., Last passed: Never
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  • ccextractor --autoprogram --out=srt --latin1 --ucla 53339f3455..., 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.

@rboy1
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rboy1 commented Dec 21, 2025

What's the root cause of the problem? what is subtitles begin half way through the video (e.g. when a new segment or show starts)?

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[BUG] Infinite binary output when processing .ts files with no subtitles

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@DhanushVarma-2 @cfsmp3 @ccextractor-bot @rboy1