Fix double application of audio/video offset for concatenated segments

[Mr-Neutr0n]

Summary

When clipping multiple segments (concatenated clips), the audio and video offsets (start_ost/end_ost) are applied twice — once when computing start/end, and again when slicing the data or computing time_acc_ost. This causes incorrect clip boundaries for any multi-segment operation.

In clip(): start and end already include the offsets after the clamping step (lines 128–129), but the data slice for subsequent segments was data[start+start_ost*16:end+end_ost*16], applying the offsets a second time. Fixed to use data[start:end].

In video_clip(): start and end already incorporate start_ost/1000.0 and end_ost/1000.0, but time_acc_ost was calculated as end+end_ost/1000.0 - (start+start_ost/1000.0), double-counting the offsets. Fixed to use end - start.

Note that the first segment in both methods was already handled correctly — the bug only affected the 2nd, 3rd, ... segments when multiple periods are matched and concatenated.

Fixes #129
Fixes #144

Test plan

• Clip a single segment with non-zero start_ost/end_ost — should behave identically to before (no change for single segments)
• Clip multiple segments with non-zero offsets — boundaries should now match the expected offset-adjusted positions instead of double-shifting
• Verify subtitle timing (time_acc_ost) aligns correctly with concatenated video clips

[gemini-code-assist]

Summary of Changes

Hello @Mr-Neutr0n, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a critical bug where audio and video offsets were applied twice during the clipping of concatenated segments, leading to incorrect clip boundaries and subtitle timings. The changes ensure that offsets are correctly accounted for only once, improving the accuracy of multi-segment audio and video processing.

Highlights

• Audio clipping logic: Corrected the clip() function to prevent double application of audio offsets (start_ost/end_ost) when concatenating multiple segments, ensuring data[start:end] is used instead of data[start+start_ost*16:end+end_ost*16].
• Video clipping and subtitle timing: Fixed the video_clip() function's time_acc_ost calculation to avoid double-counting video offsets, changing the formula from end+end_ost/1000.0 - (start+start_ost/1000.0) to end - start.
• Scope of fix: Ensured that the fix specifically addresses issues in the 2nd, 3rd, and subsequent segments during multi-segment operations, as the first segment was already handled correctly.

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Changelog

• funclip/videoclipper.py
  • Corrected audio data slicing to prevent double application of offsets for concatenated segments.
  • Adjusted time_acc_ost calculation to avoid double-counting offsets for video clips, ensuring accurate subtitle synchronization.

Activity

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[gemini-code-assist]

Code Review

This pull request addresses a critical bug where audio and video offsets were applied twice when clipping multiple concatenated segments. The changes in funclip/videoclipper.py correctly resolve this issue.

In the clip function, the redundant offset application during data slicing for subsequent segments is removed, which prevents incorrect audio clip boundaries.

Similarly, in the video_clip function, the calculation for time_acc_ost is corrected for both the first and subsequent segments to prevent double-counting the offsets, ensuring correct subtitle timing for concatenated video clips.

The fixes are accurate, well-targeted, and directly address the problem described in the pull request description. The code changes are of high quality.